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WOOD FLOORS

FOR DWELLINGS

Prepared by

FOREST PRODUCTS LABORATORY

Agriculture Handbook No. 204

U.S. DEPARTMENT OF AGRICULTURE

September 1961

FOREST SERVICE
CONTENTS

Page

Properties of wood as a finish flooring 1

Importance of moisture content 1

Developments in wood ñooring and in use conditions. 2

Guide to selection of wood flooring 3

Strip flooring 3

Plank flooring 3

Block flooring 3

Special patterns 3

Woods used for flooring 3

Hardwoods 4

Softwoods 5

Types and grades of wood strip flooring 5

Types 5

Grades and sizes 7

Types and grades of wood block and plank flooring. _ 10

Block flooring 10

Plank flooring 12

Species 12

Sizes 12

Floors laid over wood joists 12

Protection of basementless areas 12

Thesubñoor 12

Faee

Installation of the finish floor 14

Floors over concrete slabs 20

Requirements for slabs 20

Dampproofing of slab 20

Moisture content of wood flooring on concrete slab.. 23

Flooring installed in mastic 23

Selection and use of mastic adhesives for bonding

wood flooring to concrete 24

Floors laid over sleepers 31

Wood floors below grade 32

Finishing and maintaining wood floors 32

General requirements 32

Sanding 33

Staining 36

Filling 37

Choice of final finish 38

Application of final finish 39

Cracks in floors 41

Refinishing floors 42

Floor maintenance 42

Eliminating squeaks in floors 43

Experimental flooring types 44

Gro*(h Tliiough Agricultural Progress

This handbook supersedes Circular No. 489, Selection, Installation, Finish, and Maintenance of

Wood Floors for Dwellings.

For sale by the Superintendent of Documents, U.S. Government Printing OflBce. Washington 25, D.C.—Price 35 cents
WOOD FLOORS FOR DWELLINGS

Prepared by Forest Products Laboratory/ Forest Service

Wood possesses a variety of properties that

make it a highly desirable flooring material for

liomes. Its popularity has continued over the centuries. Wood is still the most extensively used

flooring material for homes. Today's markets

provide a better basis than ever for the selection

and installation of attractive and serviceable wood

floors for the modern home. Not only is selection

available from a wide variety of woods and grain

characteristics, but also from a considerable number of distinctive flooring types and patterns.

Wood flooring constitutes a prime market for

many millions of board feet of high-quality hardwoods and softwoods in the United States each

year. Because of its importance for home use, the

Forest Products Laboratory has for a number of

years conducted research on wood flooring with

"the primary aim of making it an even more satisfactory product. Much of this research has been

focused on improved seasoning and other means of

making wood more dimensionally stable, on improved methods of installation, and on development of new and cheaper ways of using wood as

flooring. Some results of this research, together

with related information on installation, finishing,

and maintenance, are presented in this publication

as an aid to producei-s and users of wood flooring

in homes.

PROPERTIES OF WOOD AS A FINISH FLOORING

The term "finish flooring" applies to the material, other than rugs or carpets, that forms the

wearing surface over the structural part of a

floor. The extensive use of wood for finish flooring indicates that it possesses in high degree the

special properties, qualities, and characteristics

that are particularly desirable for this service.

These include distinctive and attractive appearance, with wide latitude for adaptability to the

style and decorative motif planned for the home;

good hardness and wearing qualities, yet with a

degree of resilience that provides foot comfort ;

low heat conductivity, which insures a feeling of

warmth to the touch; simplicity and facility of

installation ; relative freedom from slipperiness,

depending on the finish used ; and ease of maintenance. These qualities contribute, in varying degree, to pride of ownership and satisfactory service when wood floors are properlj' installed. They

account for the fact that wood flooring has been

used in countless homes for hundreds of years.

The special feature of wide choice in appearance

and other properties available in wood flooring results from the many species of Avood and various

grades that are regularly manufactured to meet

practically any requirement, from polished brilliance to attractive natural finish. Other surface

finishes can alternatively be applied to make the

wood floor easily adaptable to any desired scheme

of interior decoration. The floor can serve as a

background to reflect the decorative motif of the

house. The inherent distinctive grain, texture,

and depth of color of wood can be made to blend

easily and naturally with the color tones of the

walls, furniture, drapery, and rugs to create an

environment that embodies all that the word

"home'' stands for.

IMPORTANCE OF MOISTURE CONTENT

The one property of wood that must be given

special attention _for flooring is its tendency to

shrink and swell as its moisture content changes.

'Maintained at Madison, Wis., in cooperation with the

L nivarsity of Wisconsin. Members of the Laboratory

staff who contributed to the preparation of this publication are as follows : Don Brouse, Forest Products Technologist; F. L. Browne, Chemist; E. M. Davis, Forest

Products Technologist; H. W. Eickner, Chemical Engineer; A. D. Freas, Assistant to the Director; L. J. Markwardt. Assistant Director ; and L. V. Teesdale, Engineer.

There are many ways to minimize and control this

characteristic, and modern selection, seasoning,

and installation methods have contributed greatly.

Control factors include the choice of edge-grain

over flat-grain material (fig. 1) ; the use of special

flooring patterns ; the development of dimensionally staole crossbanded types ; proper moisture content at time of installation; and, when necessary,

consideration of finishes that retard moisture

change. Various means of insuring satisfactory
U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

EDGE GRAIN

FLAT GRAIN

CROSS SECTION OF LOG

FIGURE 1.—Cross section-of log showing annual growth rings and position from which (A) edge-grain flooring and (B)

flat-grain flooring are obtained.

installation and service of wood flooring are

presented.

In a modern home, wood is commonly used in

neai'ly all rooms above grade, the most frequent

exception being the bathroom. Other flooring is

often employed also in the kitchen, or the kitchen

wood floor may be overlaid Avith other materials.

Improved methods of protecting wood from

dampness have encouraged its use in basement recreation rooms.

DEVELOPMENTS IN WOOD FLOORING

AND IN USE CONDITIONS

Early flooring was mostly of softwood, because

of its availability and the relative ease of working it with liandtools. Largely, too, it was in the

form of random-width planks as they came from

the mill. The production of hard^voods that afforded better wear soon followed improvements

in manufacturing equipment and seasoning methods. As a result, the use of hardwoods as flooring

expanded to where they now provide by far the

greater proportion of the total.

Strip flooring was for a long time the only type

available, and still accounts for a large proportion

of the wood flooring used. Though the early patterns of machine-made strip flooring were very

similar to those in use today, there has actually

been substantial improvement in seasoning and

manufacturing procedures in recent years, which

is reflected in improved quality.

For years, the supporting framework for floors

was made of wood not only in houses but in most

other buildings, and permitted the simple attachment of wood floors by means of nails. Changing

construction practices, first in commercial buildings and later in houses, introduced other supporting materials, notably concrete, which have

required new ways of attaching the flooring to the

supporting structure.

One method in common use for laying strip

flooring over a concrete base involves the installation of wood sleepers, generally of 2- by 4-inch

material, to support the flooring and serve as a

nailing base. The sleepers are fastened to the

concrete by anchors or mastic. The expanded use

of concrete floor slabs also encouraged the development of many new patterns or forms of wood

flooring that could be laid directly on the concrete

Avith a mastic adhesive. The early types were

short lengths of standard strip flooring sometimes

laid in a herringbone pattern or assembled in small

squares, blocks, or tiles, with the grain direction

of adjoining squares being alternated as they are

laid on the floor.

More recently, blocks or tiles have been made of

3-ply hardwood plywood in a number of thicknesses and with tongued and grooved edges. Several types of small, thin blocks or strips, some

mounted on a supporting membrane for ease of

handling, are now being marketed. Flooring tues

made from dimensionally stabilized hardwood

veneer are also available. They are laid directly

in mastic.

Changing conditions in the building industry

have created a demand for factory-prefinished

flooring, particularly for installations where the
WOOD FLOORS FOR DWELLINGS

floor must be available for service immediately

after installation. Because of improvements in

seasoning practice, precision machining, and the

development of suitable floor finishes, the flooring

industry can supply prefinished flooring that is

ready for use when laid.

GUIDE TO SELECTION OF WOOD FLOORING

Various types of wood flooring are described in

some detail in later sections. The most important

points relating to selection are outlined briefly

below as a quick guide to the prospective user.

Strip Flooring

Strip flooring is the most widely used and generally the most economical. It is available in

standard patterns and grades in both hardwoods

(oak and maple most common) and softwoods

(Douglas-fir and southern pine most common).

Hardwoods are available prefuiished. Strip flooring is most commonly laid by nailing on wood subfloor over wood framing or on sleepers set on concrete slabs. This flooring is usually side and end

matched for blind nailing, but is also available in

square-edge, which is face nailed. Special types

are available for laying in mastic in herringbone

and other floor ¡patterns.

Plank Flooring

Plank flooring is similar in pattern to strip

flooring, but comes in wider, random widths, and

is sometimes cross laminated for greater dimensional stability. It is available only hardwoods,

but in both the unfinished and prefinished forms.

Plank flooring is more expensive than strip flooring. It is usually laid on wood subfloor by blind

nailing. Sometimes it is also fastened by screws,

with the screwheads commonly covered by wood

plugs, usually of contrasting color. Plank flooring is not normally laid directly on concrete slab,

but can be put on sleepers.

Block Flooring

Block flooring is available most commonly as

squares in two general types—unit and laminated

block. Unit block is made up of strips, commonly

of standard pattern, splined or otherwise fastened

together. Laminated block is crossbanded like

plywood, and shrinks and swells less with moisture

change than do other flooring types. Both general types of block flooring are available in a variety of hardwood species (oak most common),

either unfinished or prefinished.

Block flooring may be laid on wood subfloor by

nailing or by laying in mastic, or on concrete

coated with mastic. The grade designations for

unit block flooring generally correspond to those

for strip flooring, but the designations for laminated block flooring frequently vary with the

manufacturer. Sizes available range from about

6% by 6% to about 12 by 12 inches, with 9 by 9

inches being the most common.

Special Patterns

There are many special patterns that do not fit

into the classifications just given. One is a thin

veneer tile designed for laying in mastic much like

resilient flooring. Designed to have improved

dimensional stability, this tile is available in a

limited number of hardwoods.

WOODS USED FOR FLOORING

About a dozen woods are regularly worked to

pattern as flooring. Among these are five hardwoods,- namely, oak (including species of both the

''Although the terms "hardwoods" and "softwoods" are

the most generally accepted popular names for the two

broad groups of trees cut for lumber, they are rather misleading to the layman, because they bear no relation to

the actual degree of hardness or softness of the wood.

Cottonwood, aspen, basswood, and yellow-poplar are all

classed as hardwoods, and yet each is softer than longleaf

pine, which is classed as a softwood. Similarly, yew is

classed as a softwood but is four times as hard as basswood

and considerably harder than many of the oaks. The

means employed by botanists and wood technologists to

separate the two groups are also difficult for the layman

to understand. Perhaps the most accurate and most

■■eadily interpreted definitions are "trees with broad

eaves" for hardwoods and "trees with needles or scalelike

leaves" for softwoods. The softwoods are also sometimes

called conifers, because they bear cones.

red and the white oak groups), maple, beech, birch,

and pecan. The rest are softwoods, comprising

southern pine, Douglas-fir, western hemlock, western larch, and redwood.

Although redwood is not high in hardness, its

heartwood is quite decay resistant. Such redwood

flooring as is regularly manufactured is intended

mainly for porches and similar locations where

the wood is exposed to the weather and the decay

hazard is high.

Of the other softwoods listed, Douglas-fir and

southern pine are those most generally used for

flooring in house construction. Hardwoods are

generally more popular as a flooring material than

are softwoods, partly because of their greater resistance to wear and the natural figure which lends

beauty to the finished floor.
U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

Hardwoods

Oak and maple are the principal hardwoods used

for flooring, with beech, birch, and pecan ranking

next in quantity. Each piece of hardwood floorino- usually bears the trademark of the trade association under whose rules it was graded, the grademark, and the name, number, or symbol of the

member mill that manufactured it.

Figures show that 1,200,000,000 board feet of

hardwood flooring were produced in 1954. This

is 80 percent of all flooring produced, both hardwood and softwood. Oak of various commercial

species supplied 92 percent of this hardwood flooring, as compared with 6 percent for maple. The

remaining 2 percent consisted largely of beech,

birch, and pecan. The small-scale use of sweetgum, ash, hickory, túpelo, cherry, locust, walnut,

basswood, and aspen for flooring has also been

reported. Their combined use, however, Avas less

than 1 percent of the total for all hardwoods.

Oak

There are about 20 species of oak in the United

States that may be considered commercially important in lumber production. Of these, about

half are classed as red oaks and the rest as white

oaks. This classification of oak into red and white

is standard practice commercially in the lumber

trade. In the growing tree the differentiation of

red oak from white oak is based on botanical characteristics, such as form of the fruit, flower,

leaf, and appearance of the bark. In lumber,

identification of the oaks is more difficult.

Most species of oak cut into commercial lumber

are used in the manufacture of flooring. They

grow under a wide range of climatic conditions in

many different kinds of soil. There is, accordingly, much variation in the color of the wood, especially the heartwood; the sapwood usually

shades from white to cream color in all species of

oak. In the standard grading rules for oak flooring, color is entirely disregarded except in the

amount of light-colored sapwood allowed. Sapwood is limited only in the best grade of flooring.

Should a reasonable degree of color uniformity

be desired, it can be obtained by selecting the flooring strips for each room that most nearly match in

color tone, rather than by laying them at random

just as they come from the bundle. If an absolutely uniform color is wanted, special arrangements should be made with the dealer or contractor. The grading rules do not differentiate between red oak and white oak, but the industry is

prepared to supply all-red oak stock or all-white

oak stock, at a slightly higher cost for selection.

As a general rule, red oak flooring is lower in price

and more uniform in color than white oak.

A special feature of v'liite oak is the prominence

of large rays that make an interesting flake pattern

in quartersawed flooring. In certain parts of the

united States the preference is for white oak, in

others red oak is more in demand. Red oak and

white oak are about equal in general properties.

Both make a very satisfactory floor of attractive

appearance when properly finished.

Maple

Maple flooring is made from sugar maple {Acer

saccharuon) ^ and also from black maple {A.

nlgrum), formerly considered as a variety of sugar

maple. The production of lumber from these

species centers largely in the Lake States, the

Northeastern States, and the Appalachian States.

The trade name for both species is "hard maple";

occasionally they are called rock maple. The socalled soft maples—silver maple, red maple, and

the western species, or bigleaf maple—are not so

hard, heavy, or strong as hard maple, and because of this are not commonly used for flooring.

In addition to being heavy, strong, hard, and stiff,

hard maple wears well under abrasion and takes

an excellent finish. These properties fit it well for

flooring.

The heartwood of both species of hard maple

is light reddish brown, and the sapwood, which

in mature trees is several inches thick, is white,

slightly tinged with brown. The contrast in color

bî-tween heartwood and sapwood in maple is much

less pronounced than it is in oak. In the standard

grading rules for maple flooring, the varying

natural color of the wood is allowed except in

special grades.

Beech and Birch

In comparison with hard maple, beech and more

especially birch are used only sparingly in the

manufacture of flooring. Only 2 of the 15 or

20 species of birch that grow in the United

States are manufactured into flooring. Of these,

yellow birch {Betida nlleghaniensü) is by far the

most abundant and most important commercially.

The other is sweet birch {B. lenta). Only one

species of beech {FaguH grandifolia) is native to

the United States. The heartwood of all three

of these woods is reddish brown, with a slight

variation in color for each individual species.

Similar slight variations exist also in the color of

the sapwood of the three species, which is of a

lighter shade than the heartwood. As in maple

flooring, the natural varying color of the wood is

an accepted characteristic in grading beech and

birch flooring. >

Other Hardwoods \

The five hardwoods described above supply [

about 99 percent of all hardwood flooring. The

remaining 1 percent is divided among at least 8 .

native species, including sweetgum, ash, hickory, I

sycamore, túpelo, cherry, locust, and walnut. Some

of these were probably used more because of ready

availability than because of any special characteristics. Cherry and walnut together with some

exotic woods like mahogany and teak are used

largely in parquetry flooring for ornamental etiect 'h
WOOD FLOORS FOR DWELLINGS

because of their color and grain. None of the

above is specifically mentioned in grading rules.

Softwoods

The volume of softwood flooring produced in

1954 was 316 million board feet, or 20 percent

of all flooring. In 1948, 52 percent of the softwood flooring was southern pine, 41 percent

Douglas-fir, and 4 percent western hemlock. The

remaining 3 percent was divided among the following 8 species, listed in order of volume : Eastern white pine, ponderosa pine, western larch,

eastern hemlock, redwood, spruce, cypress, and

the true firs. Some of these species could hardly

be recommended where wear is an important factor. The total output of softwood flooring has

remained fairly constant, and the chief species

have maintained their positions.

Southern Pine

Southern pine is a name applied to a group of

yellow pines that grow principally in the Southeastern States. The group includes longleaf,

shortleaf, loblolly, slash, and Virginia pines and

several others of minor importance. Except in

dimension material and structural timbers, no differentiation in species is made commercially in

marketing the products from this group of woods.

The wood of all southern pines is much alike

in appearance. The sapwood and heartwood are

frequently, although not always, distinctly different in color, the former being yellowish white and

the latter a reddish brown. The contrast, in color

between sapwood and heartwood in southern pine

is not generally strongly marked in a finished

floor, and the standard grading rules for southern

pine permit sapwood in all grades of products

manufactured, including flooring, unless otherwise stated.

Should flooring of uniform color be essential, it

would be necessary to add a requirement to the

standard flooring specifications to obtain this special stock; i.e., only all-sap-face stock to secure a

light-colored floor, or all-heart-face material to

obtain a reddish-brown floor. However, such a

modification of the standard specification for flooring requires special selection of stock for color

and, therefore, the cost is higher than that of the

established grade.

Douglas-Fir

Douglas-fir, which grows in the western part of

the United States and Canada, is occasionally

called red fir, coast Douglas-fir, or Oregon pine.

Douglas-fir occupies the same important position

in tlie Western and Pacific Coast States that

southern pine does in the Southeastern States.

The sapwood of Douglas-fir is creamy white.

The heartwood is reddish brown, and as with

southern pine, the contrast in color between the

two is not so pronounced as to be objectionable

in a finished floor. Pieces containing both heartwood and sapwood are admitted in all grades.

Western Hemlock

Western hemlock grows along the Pacific Coast

from northern California to Alaska and as far inland as northern Idaho and northwestern Montana. The bulk of that produced comes from

Washington. This wood is commercially called

west-coast hemlock. Both the heartwood and sapwood of western hemlock are almost white with

a pinkish tinge and with very little contrast, altliough the sapwood may sometimes be lighter in

color.

Western hemlock has a combination of properties that make it usable for manj' types of flooring. Its light, clear color, and good finishing

qualities are accountable for its use in flooring

where good ajDpearance under moderate wear is

tlie principal requirement. Altliough it withstands reasonable abrasive or impact service, it

mars and dents more readily than the hardwoods

and the more commonly used softwoods, such as

southern pine and Douglas-fir. Western hemlock

flooring is relatively free from warping, and is

easy to cut and nail. Experience with western

hemlock as a high-grade finish floor, however, has

been confined largely to its use as an alternate

for hardwoods in bedrooms. For the most part,

the use of western hemlock flooring has been confined to the regions of its production.

Other Softwoods

The remaining 3 percent or so of all softwood

flooring is supplied by 8 other species. Western

larch is similar to Douglas-fir in strength properties, and is often sold in mixture with Douglas-fir

of the northern interior States. Some of the species, like ponderosa pine, eastern white pine, and

redwood, are softer than is desirable where wear

is a factor. Where the flooring will be covered,

as with linoleum, this obje^-tion would not hold.

The decay resistance of redwood in the all-heart

grade has prompted its use for porch flooring.

Eastern hemlock, spruce, cypress, and the true firs

also are made into flooring on a small scale.

TYPES AND GRADES OF WOOD STRIP FLOORING

Types

Hardwood flooring is manufactured in a variety of widths and thicknesses, most commonly

>n what IS known as the standard pattern. The

896018 0—61 2

most widely used standard pattern is ss/^^ inch

thick and has a face width of 2y^ inches, but other

widths and thicknesses are available in this pattern. One edge has a tongue and the other a

groove, and the ends are similarly matched (fig.
6

U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

M-

-FACE WIDTH

THICKNESS V> ' ' ^' ' ^' i ^^ ^ ^ '' \

A

THICKNESS

B

THICKNESS

c

THICKNESS-^/JH/

D

THICKNESS

i

E

THICKNESS

F

FIGURE 2.—Tyi)es of flooring : A, Side and end matched ; B, side matched, plain end ; C, square edged ; Z), scratch backed,

sometimes used on softwood flooring ; E, flat backed with notched recess for laying directly in mastic ; F, flooring

with spline.

2, A). The strips are random length, varying

from 1 to 16 feet in length in separate bundles.

The proportion of short pieces will depend on the

grade used. Some softwood flooring is sidematclied only, the ends being square (fig. 2, B).

Flooring of standard pattern is generally hollow backed (fig. 2, J. ) or scratch backed (fig. 2, Z) ).

The top face is generally slightly wider than the

bottom, so tliat when the strips are driven tightly

together, the upper edges make contact but the

lower edges are slightly separated. Standard

pattern flooring may be installed over Avood framing by nailing to the subfloor or to wood strips or

sleepers over a concrete base. This type of flooring is commonly installed by blind nailing at the

intersection of the tongue and shoulder, so that no

nails show in the finished floor.

Another pattern of strip flooring used to a

limited degree has square edges and a flat back

(fig. 2, G). This is generally thinner than the

standard pattern and is uaaally installed by face

nailing. The nails are driven and set so the floor

filler used in finishing will fill and conceal the lióles.

The majority of strip flooring is laid by concealed or blind nailing to wood subfloors or to wood

sleepers. While some strip flooring is laid directly in mastic on a concrete base, largely using

short lengths in special designs such as herringbone, it is more common, for this type of base, to

use special patterns specifically designed for laying in mastic (fig. 2, E and F). Generally, these

have flat backs for greater contact with the adhesive and, in addition, a recess milled into the lower

surface below the tongue to reduce the possibility

of mastic being forced up through the opening

between adjacent strips and thus staining the

wearing surface.

Some square-edged and flat-backed flooring is

made for laying in mastic. This generally is

grooved on the edges for insertion of a spline and

has a mastic trap on the side (fig. 2,/^).

Softwood flooring is made both end matched

and with plain ends. It is made with a holloa

back, or sometimes with a single V-shaped groove

in the back ( fig. 2, Z> ).
WOOD FLOORS FOR DWELLINGS

Grades and Sizes

Standard flooring grades are based almost

wholly on appearance. That is, they exclude or

severely limit such defects as knots, wormholes,

and the like in the higher grades and permit increasing sizes and numbers of these characteristics

in the lower grades. Natural variations in color

are generally not limited except that, in certain

grades, the amount of the lighter colored sapwood

is restricted. Special grades, selected for color,

may be obtained in maple, beech, and birch. This

is generally limited to the highest grade (clear) in

which all-sap or all-heart maple and all-heart

beech or birch may be obtained. The extra selection for color increases the cost of these special

grades as compared with the standard grades.

Oak

Oak is regularly manufactured into plainsawed

and quartersawed flooring. Most of the oak flooring used is plainsawed, the lower priced of the

two. Quartersawed oak is characterized by a

rather striking figure, and by a minimum shrinking and swelling in width. The term rift-sawed

has come into common use in recent years. In

practice, this means a type intermediate between

true plainsawed and true quartersawed, and produces a less striking figure than the latter. Oak

flooring is graded under the rules of the National Oak Flooring Manufacturers' Association

(table 1).

TABLE L—Grade; description, and dimensions ' of oak flooring -

Kind of

Grade

.Standard

flooring

Name Description

length

Quartersawed-_

Do

Plainsawed

Do

Do

Clear

Select

Clear

Select

No. 1 Common.

The face shall be practically clear, admitting an average of Yt inch of

bright sap. The question of color shall not be considered.

The face may contain burls, small streaks, pinworm holes, slight

imperfections in working, and small tight knots that do not average more than 1 to every 3 feet.

The face shall be practically clear, admitting an average of % inch of

bright sap. The question of color shall not be considered.

The face may contain burls, small streaks, pinworm holes, slight

imperfections in working, and small tight knots that do not average more than 1 to every 3 feet.

Shall be of such nature as will lay a good residential floor and may

contain varying wood characteristics, such as flags, heavy streaks

and checks, wormholes, knots, and minor imperfections in working.

Feet

2 and up; av.,

4M.

2 and up; av.,

2 and up; av.,

4M.

2 and up; av.,

2,%.

2 and up; av.,

3.

' All grades are made in the following combinations of thickness and width :

zs^j-lnch thickness, SH-, 2¡.4-, 2-, and IH-inch widths; H- and %-inch thicknesses, 2- and IH-inch widths.

' Data are from rules of the National Oak Flooring Association in efïect

June 17,1957. All flooring listed is kiln-dried, grade-marked, trade-marked,

hollow backed, and side and end matched. For lower grades than those

listed above and for square-edge strip flooring, see the latest issue of the grading rules of the National Oak Flooring Manufacturers' Association, 814 Sterick

Bldg., Memphis, Tenn.

By far the most common thickness for oak flooring used in homes is ^%2 inch, although thinner

flooring is available for use where sendee is light

or for installation as replacement over existing

floors. Flooring thicker than 2^2 inch is made,

but is intended for use under heavy service rather

than in homes.

Although the great bulk of oak strip flooring

is end and side matched, some square-edge strip

flooring is made. The grades are the same, but

the thicknesses and widths differ, as indicated

below:

Tluckness ' Width

[inch) -•" '' (inches)

%6 '/a, 1, IVa, ly*, IVs, 11/2, 2

% 11/2, 2

Three grades of prefinished flooring are recognized: Prime, Standard, and Tavern. In prefinished flooring, the red oak and white oak are

separated after sanding and finishing.

Maple, Beech, and Birch

Flooring of these species is gi'aded under the

rules of the Maple Flooring Manufacturers' Association and also under the rules of the National

Oak Flooring Manufacturers" Association (tables

2 and .3). The requirements under both sets of

rules are essentially the same. Both generally

disregard normal color variations, but, as indicated earlier, special grades are available in

which uniformity of color is a requirement.

Most of the teech, birch, and maple flooring

used in homes is in the ^s/g^-inch thickness, but

thinner sizes are available for use where service

is light. Thicker flooring is made, but is not generally used in homes.

In addition to the more common end- and sidematched flooring, some square-edge (or jointed)

flooring; is made. Thicknesses are the same as for

the standard pattern (%, 1/2, %, and -'•'5/32 inch),
8

U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

TABLE 2.—Grades, description, and dimensions ^ of northern hard maple, beech, and birch flooring ^

Kind of wood

Grade

Standard length

Name Description

Rppch birch and First grade . . Shall have the face practically free from all defects,

but the varying natural color of the wood shall not

be considered a defect.

Will admit tight sound knots and slight imperfections

in dressing, but must lay without waste.

Special stock selected for uniformity of color. It is

almost ivory white and is the finest grade.

Special stock selected for uniform brown color. It

has more grain pattern than other types.

Made from all-red-faced stock especially selected for

color.

Feet

2 and up. Not over

30 percent under 4

feet.

2 and up. Not over

maple.

Do Second grade

Selected first grade,

light northern

hard maple.'

Selected first grade,

amber northern

hard maple.'

Selected first grade,

red.'

Maple

45 percent under 4

feet.

2 and up. Not over

Do

30 percent under 4

feet.

Do.

Beech and birch.. Do.

' All grades are made in the iollowing combinations of thickness and width :

ä%2-inch thickness, 3H-, 2^-, 2-, and IH-inoh widths; 5á-, î^-, and H-inch

thicknesses, 2M-, 2-, and IH-inch widths.

2 Data are from grading rules of the Maple Flooring Manufacturers' Association in effect December 4,1956. AH flooring listed is kihi-dried, grade-marked,

but the widths differ somewhat, being 214, 2i^, 3%,

3%, and 3I/2 inches.

The first grade is especially suitable where fine

appearance and high wear resistance are both desired. The second grade is about equally serviceable, but because of small imperfections does not

present so good an appearance. The third grade

trade-marked, and side and end matched. The hollow back is optional.

For lower grades than those listed above and for jointed (square-edge) flooring,

see the latest issue of the grading rules of the Maple Flooring Manufacturers'

Association, 35 East Wacker Drive, Chicago, 111.

' Special grade.

is chieñy used where the main requirement is

service rather than appearance.

Southern Pine

Southern pine is regularly manufactured in sideand end-matched flooring and also in plain-end

flooring that is side matched only. All southern

TABLE "3.—Grade, description, and dimensions ' of beech, birch, hard maple, and pecan flooring ^

Kind of wood

Grade

Standard length

Name Description

Beech, birch, and First grade . Shall have the face practically free from all defects,

but the varying color of the wood shall not be a

defect.

Will admit tight sound knots and slight imperfections

in dressing, but must lay without waste.

Special stock selected for uniformity of color. It is

almost ivory white and is the finest grade.

All-red-faced stock especially selected for color

Shall be practically free from defects, but the varying

natural color of the wood shall not be considered a

defect.

Same as first grade except that face shall be all

heartwood.

Same as first grade except that face shall be all bright

sapwood.

Will admit tight, sound knots or their equivalent,

pinworm holes, streaks, light stain, and slight

imperfections in working. Shall be of such nature

as to lay a sound floor without cutting.

Feet

2 and up. Not over

30 percent of 2 and

3.

2 and up. Not over

45 percent of 2 and

3.

2 and up. Not over

30 percent of 2 and

3.

Do.

2 and up. Not over

25 percent of 2 and

3.

2 and up. Not over

25 percent of 2 and

3.

Do

maple.

Do Second grade

First grade, white

hard maple.

First grade, red

beech and birch.

First grade

Maple

Beech and birch..

Pecan

Do First grade, red

First grade, white

Second grade

Do

Do VA and up. Not

over 40 percent of

lYi to 3.

1 AU .çrc-rles are made m the iollowing combinations of thickness and width:

2^2-mch thickness, 3»-, 2)4-, 2- and IH-inch widths; U- asc! H-inch thicknesses, 2- an<l lU-inch widths.

» Data are from gradiug rules oí the National Oak Flooring Manufacturers'

Association in efieot June 27, 1957. All flooring listed is kiln-d?ied, ¿ademarked, trade-marked, hollow backed, and side and end matched. For

lower grades than those listed above and for jointed (square-edge)^ ""K'

see the latest issue of the grading rules of the National Oak Flooring Manufacturers' Association, 814 Sterick Bldg., Memphis, Tenn.
WOOD FLOORS FOR DWELLINGS

TABLE 4.—Grades, descriptions, and dimensions ' of southern pine flooring ^

9

Kind of flooring

Grade

Standard length

Name Description

Flat-fftain A Clear or practically clear, requires best manufacture, and

admits very small surface checks and very light warp.

Admits checks, small surface checks; firm red heart, on

not over 5 percent of face; knots, one sound-intergrown

pin knot in any 4 feet of length in 4 to 20 feet or one in

each piece if under 4 feet long; manufacture, standard

B manufacture; pitch, one very small closed pitch

pocket and one small pitch streak in any 4 feet of length

in 4 to 20 feet or one in each piece if under 4 feet long,

diffused general pitch not permitted; stain, light stain

only and on not over 15 percent of face; warp, light

warp.

Admits somewhat larger and more numerous characteristics than B.

Same as for flat-grain, except lumber has an average of

at least six annual rings per inch across its face at each

point in length, and the annual rings form an angle of

45° or more with the face. When the angle becomes

less than 45° at any point, the lumber may be classed

as flat-grain or near-rift, as the case may be.

Same as for flat-grain, except lumber either has fewer

rings per inch than required in edge-grain but otherwise

conforms to the edge-grain provision, or has an average

of at least six annual rings per inch across the face at

each point in the length and has only one edge of the

grain on the face but forms an angle of less than 45°

with the face side.

Feet

4-20 with 5 percent

B

of 8 and/or 9.

Do.

Edge-grain (or

vertical-grain).

Near-rift- - -

C

A, B, and

C.

A, B, and

C.

4-20 with 5 percent

of 6 and/or 7 and 7

percent of 8 and/or

9.

4-20.

4-20.

' Made in thicknesses of 5Í8, Me, Ms, and 3§Í2 inch and in widths of Hi,

2M, ÎM, iVi, and 5M inches.

' Data are from the rules of the Southern Pine Association in elïeot June 1,

1956. Specifications apply to kiln-dried flooring. It may be plain-end or

end-matched. Unless otherwise specified, orders are construed as applying

to plain-end, flat-grain, or mixed grain. Standard working is either scratch

backed or hollow backed. Grade-marking and trade-marking are optional.

pine flooring, irrespective of how it is worked to

pattern, is available in both flat-grain ^ and edgegrain* stock (fig. 1). A class of southern pine

flooring intermediate between edge-grain and flatgrain stock is known as near-rift flooring (table 4).

This is not flat grain, and yet the angle of the rings

in such flooring does not meet the requirements for

edge-grain material. Because of this fact, one of

the grade requirements for near-rift flooring is

that it must show an average of six or more annual

growth rings measured anywhere across the face

of the piece.

Edge-grain southern pine flooring, because of its

better wearing quality and the more pleasing appearance of its uniform grain pattern, is suited to

the rooms on the living floors of the house, while

the flat-grain stock adequately meets the requirements of bedroom floors. Southern pine flooring

Flat-grain lumber is that in which the annual rings

form an angle of less than 45° with the surface of the piece,

ííynonymous terms : Flat-sawed, plainsawed.

Edge-grain flooring has at least 6 annual rings across

Its face, and the annual rings form an angle of 45° or

more with the surface of the piece. Synonymous terms :

Kift-grain, vertical-grain, quartersawed.

is graded under the rules of the Southern Pine

Association (tableé).

Douglas-fir

With the exception of the B and Better grade,

which is manufactured only from vertical-grain

material, Douglas-fir flooring in the upper grades

is regularly manufactured in both vertical-grain

and flat-grain stock. B and Better Douglas-fir

flooring is also selected for density, allowing only

such m.aterial as shows not less than six annual

growth rings per inch on either end of the piece.

As does southern pine, vertical-grain Douglas-fir

possesses better wearing qualities than does flatgrain Douglas-fir flooring. Douglas-fir flooring is

tongued and grooved, but not end matched. All

flooring of this species is graded under the rules of

the West Coast Lumbermen's Association

(table 5).

Western hemlock

The grades of western hemlock flooring are identical with those for Douglas-fir. It, too, is graded

under the rules of the West Coast Lumbermen's

Association (table 5), as are spruce and western

redcedar flooring.
IQ U.S. DEPT. OF AGRICrULTÜRE HANDBOOK NO. 204

TABLE 5.—Grades, descriptions, and dimensions ' of Douglas-fir and western hemlock flooring '

Kind of flooring

Grade

Standard length

Name Description

Vertical-grain (edgegrain).

B & Btr

CPieces of this grade are of sound wood and are vertical

grain, with not less than 6 annual rings per inch-.

Most pieces are entirely clear or have only a few minor

and unimportant characteristics, such as very slightly

torn grain, three very small pitch pockets or their

equivalents, tongue J-íe inch narrow.

Pieces of this grade are of sound wood with not less than

4 annual rings per inch. Pieces are vertical grain

except that occasional pieces may have an angle of grain

between 45° and 60° from vertical. Pieces of this

grade may have one or more characteristics which are

of such size and number that the piece is not of "B &

Btr." grade. Some pieces may have light stain, 25

percent; two small seasoning checks; slightly torn grain;

two small, sound, tight knots or their equivalent; or

three small pitch pockets or their equivalent; tongue

Yii inch narrow. A 3-inch cutout 4 feet or more from

either end of pieces 12 feet and longer is permissible in

10 percent of the shipment if the piece is otherwise

"B & Btr."

Admits somewhat larger and more numerous characteristics than C.

Pieces of this grade are of sound wood. Most pieces are

entirely clear or have only a few minor and unimportant characteristics, such as medium stained wood;

two small seasoning checks; slightly torn grain; two

small, sound, tight knots or their equivalent; or three

small pitch pockets or their equivalent; tongue Ke inch

narrow. A 3-inch cutout 4 feet or more from either

end of pieces 12 feet and longer is permissible in 5 percent of the shipment if the piece is otherwise of a high

type.

Same as D vertical-grain _

Feet

4 to 16 or longer.

Not less than 90

percent 8 to 16 or

longer. Not more

than 3 percent 4

and/or 5.

Do.

D 4 to 16 or longer.

Not less than 80

percent 8 to 16 or

onger.

Same as B & Btr.

and C above.

Same as D above.

Flat-grain or mixed

grain.

C&Btr..-.

D

' Made in thickness of 2%2 and in widths of 2H, 3H, and SMe inches.

2 Data are from the rules of the West Coast Lumbermen's Association in

effect March 15, 1956. Specifications apply to kün-dried flooring. The

back of the pieces may be partially surfaced or hollow or scratch backed.

Grade-marking and trade-marking are optional. Western hemlock is graded

like Douglas-fir in the same grades and types of grain, with the following

exception. In describing hemlock grades, the term "bark pockets" is used

where the fir grades use the term "pitch pockets." The grading rules also

include spruce (VG and FG) and western redcedar (VG only).

TYPES AND GRADES OF WOOD BLOCK AND

PLANK FLOORING

Block Flooring

Two basic types of construction are used in the

manufacture of wood block flooring. In one,

variously called "block," "unit block," or "solid

unit block," short lengths of standard strip flooring are joined together edgewise to form square

units (fig. 3, A), generally with wood or metal

splines embedded in the lower surface. In the

second type, three or more plies of veneer are

bonded with adhesive to obtain the desired thickness, the grain direction of the center ply being

at right angles to that of the two surface plies (fig.

3, B). This latter tvpe is generally knovm as

"laminated" block or as "plywood"' block.

In addition to the two basic types described

above, there is a -variety of other constructions

too numerous to attempt to describe in det-ail. One

type, however, utilizes thin, square-edged strips

bonded to a flexible membrane, usually paper (fig.

3, 6^). In at least one instance, small squares of

wood are bonded to paper to form a mosaic pat- '

teni. The function of the paper bonded to the

upper face is simply to hold the strips or squares

as a unit until the block is laid ; it is then stripped

off. These types are generally composed of relatively small squares, a number of which are assembled for laying as a unit.

Still another type might be more properly ¡

termed a tile rather than a block. It is made oi

specially dried hardwood veneer and is from Vs

to Vio inch thick. Thus, in size and in method of

laying, it resembles the resilient tiles. The flooring ^

is made by press drying the veneer so that it is ii
WOOD FLOORS FOR DWELLINGS 11

' FiGTJKE 3.—Typical flooring blocks : A, Unit block ; B, laminated (plywood) block ; C, strips bonded to membrane.

^ restrained from shrinking during the drying

'^ process. This method results in numerous small,

J^, inconspicuous, uniformly distributed checks that

'¡''- materially reduce shrinkage and swelling across

the grain with changes in moisture content and

r make the veneer rather flexible.

'4 a "^^^^^ ^''^ "^0 generally accepted grades for block

äj flooring,^ probably because of the multiplicity of

ï^. J'f^^'al Specification NN-B^50, Block, Floor, Wood

l(!i (Solid Unit and Laminated Hardwood) describes three

patterns and constructions. The unit block, however, may generally be purchased in the same

grades as standard strip flooring, some manufacturers having, in addition, special grades. Manufacturers' literature on the laminated blocks sometimes refers to grades for the wearing surface

which indicates that they adhere to generally the

same requirements as for strip flooring, but generally in the higher grades. The laminated (plywood) block, by reason of its cross-laminated construction, shrinks and swells less than the strip.

Less difficulty from changes in moisture content

may therefore be expected.

Block flooring, whether unit or laminated, is

generally tongued on two adjoining or opposing

edges and grooved on the other two to assure

alinement between adjoining blocks. Some manufacturers produce square-edged blocks, and at

least one grooves all four edges and furnishes

splines for insertion between adjoining blocks.

Both types are designed to be installed either by

nailing to a subfloor or by laying directly in a

mastic. The membrane-supported type and the

veneer tile are designed to be laid directly in

mastic.

A wide choice of pattern is available in the unittype block flooring. The most common pattern is

that in which the strips are all laid with the grain

directions parallel. In others, however, a variety

of effects is possible by combining four sma^

squares into a single unit, by banding the edges,

and the like.

If a laminated or plywood flooring is to give

satisfactory service, the glue bonds between the

plies must be well made with glues that can withstand the probable conditions of service and remain intact during the life of the flooring. Service conditions can be expected to vary in different

areas and in the different individual installations.

In addition to the variations in moisture content

typical of interior woodwork, some parts of the

flooring may be in contact with or near sources of

heat, such as radiators, space heaters, or steam

Eipes, where they will be heated well above the

uman comfort range. In other installations in

warm, moist areas, as along the southern coast,

conditions may be damp and warm enough to

favor mold growth.

The different glues that are currently available

to the woodworkers vary rather widely in their

resistance to the various conditions of service, but

include some that are practically immune to moisture, extremes in temperature, and molds or other

micro-organisms. It is thus only necessary to employ the proper kind of glue in manufacture to

secure satisfactory bonding to meet any requirements in service.

The most resistant adhesive types are phenol

resin, resorcinol resin, resorcinol-phenol resm, and

melamine resin. Joints well made with these glues

grades for the solid unit block—Clear, Select, and No. 1

Common—that are very similar to those shown in table 1.
12 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

can be expected to withstand any type of service

for which wood itself is suitable. Their resistance

is distinctly higher than would be required by normal use of laminated flooring.

The melamine-urea resin type of glue is not so

highly resistant as those mentioned above but, if

reasonably high in melamine resin, may be expected to give results that are quite adequate for

laminated flooring.

Urea-resin glues, casein glues, soybean glues,

animal glues, starch glues, and polyvinyl glues can

form joints that are strong in the dry condition,

and some of them are moderately resistant to occasional exposure to water or to high humidities.

Because the integrity of bonds in laminated block

flooring with these adhesives cannot be assured

under all conditions of service that could be considered normal for flooring, their use is not

recommended.

As a general rule, the manufacturers of laminated flooring favor the melamine-urea resin type

as a reasonable compromise between cost and resistance to moderately severe service conditions.

The builder or the homeowner should make sure

that a suitable type of adhesive has been used in

the laminated blocks to meet his anticipated conditions of service.

Plank Flooring

Plank flooring is, in effect, strip flooring, except

in greater widths. That is, it is usually the same

thickness as strip flooring, is end and side matched,

and may be installed in the same manner. It is

generally available in random widths, and the

edges are commonly beveled to accentuate the

grooves between individual planks.

This type of flooring is designed to simulate the

appearance of the random-width planks commonly

used in colonial homes. To further simulate this

appearance, wood plugs of contrasting color are

sometimes inserted in the flooring to simulate the

wood pins once used for fastening flooring, or pegs

of various types may be set into the edges. Plank

flooring is sometimes made in laminated form—

that is, with a central cross ply. This form is

more dimensionally stable in width than the solid

form.

Species

Oak is by far the predominant species in both

block and plank flooring. Other species, such as

walnut, cherry, and teak are generally available in

the block flooring and sometimes in plank flooring. Sometimes a mixture of hardwoods, such as

hickory, ash, elm, pecan, sycamore, beech, and

hackberry, may be used at random in a single

block.

Sizes

Block flooring is available in a variety of sizes.

Thicknesses commonly are the same as strip flooring (2%2 or 134,6 inch), but thicknesses of %6i ^16)

and 1/2 inch are also available. Perhaps the most

common block size is 9 by 9 inches. Other sizes,

such as 6% by 6%, 7% by 71/2, 8 by 8, 10 by 10,

and 12 by 12, are also available.

Plank flooring is available in a considerable

range of widths, from 2^4 inches to about 8 inches. ^

Lengths are generally random.

FLOORS LAID OVER WOOD JOISTS

Protection of Basementless Areas

Special consideration is required in floors for

basementless houses having either a concrete slab

laid directly on the ground or joists supported on

foundations and separated from the soil by a crawl

space. Both of these types of construction introduct the problem of keeping moisture from entering the wood floor from the soil below.

The crawl space below the floor of a basementless house and the space below porches supported

on wood framing should be ventilated. Where

there is a partial basement with one side adjacent

to the crawl space, vents are not required in the

outer walls of the crawl space if openings between

the basement and the crawl space are equal to at

least %o of the combined area of basement and

crawl space. For crawl spaces where there is no

basement, at least four foundation-wall vents

should be provided near the corners of the buildmg and having a total free ventilating area equal

to i/ieo of the ground area (fig. 4). Vent openings should be covered with corrosion-resistant

screening having é to 8 meshes per inch.

Where a soil cover is used, such as smoothsurface roll roofing weighing at least 55 pounds

per roll of 108 square feet, with sheets lapf)ed at

least 2 inches, or other suitable vapor resistant

material such as polyethylene, only two foundation wall vents would be required. They should

be so located as to assure cross ventilation. The

free ventilating area required where the soil cover

is used would be Vieoo of the ground area. The

soil cover is recommended in all places where the

soil is consistently damp after the house is

completed.

The Subfloor

When joists or beams are used as floor supports, a subfloor should be laid over the franiing.

A subfloor serves several important functions.

It brings the tops of the joists to a common level,

helps stiffen the floor, blocks off cracks that may

develop in finish flooring, serves as a safe working surface for workmen during construction, and

provides a level base for finish floor and partition

soleplates.
WOOD FLOORS FOR DWELLINGS 13

FINISH FLOOR

VAPOR BARRIER

xJOIST

GALVANIZED CHICKEN WIRE

s^ USED TO SUPPORT INSULATION

FiGTiEE 4.—Crawl-space ventilator and soil cover.

The requirements for subflooring include good

stiffness, nail-holding power, and ease of application. Subflooring may be of nominal inch

boards or plywood. Sometimes 2-inch plank

decking is used as subflooring over beam framing.

Boards

Boards for subflooring may be of any species

of wood, and should not be less than nominal 1

inch thick nor more than 8 inches wide. The

optimum moisture content is about 12 percent in

most parts of the United States. No. 3 Common is the minimum grade for such species as

Douglas-ñr, southern cypress, western hemlock,

redwood, the cedars, eastern hemlock, tamarack,

and southern yellow pine. No. 4 Common is the

minimum grade for white fir, western larch,

spruce (except Sitka), ponderosa pine, sugar pine,

Idaho white pine, eastern white pine, and red pine.

i^. Square-edged, shiplap, or tongued-and-grooved

boards may be used. Tongued-and-grooved endmatched boards of random length are used, but

must be long enough so that each board will bear

on at least two joists and so installed that end

'j joints of adjacent boards will not occur between

,' the same pair of joists. With square-edged or

i; shiplap boards, end joints should always be made

.' over a joist. Boards less than 8 inches wide

;. should be nailed at each joist with 2 eightpenny

'i ^^ ^^i^ 8-inch boards with 3 nails. Boards may

^' T. applied diagonally or at right angles to the

•, ]oists, but commonly they are laid diagonally,

w since this method provides greater bracing.

806018 0—61 3

The joist spacing should not exceed 16 inches,

center to center, when finish strip flooring is laid

parallel to the joists or the finish floor consists of

parquet, block, or floor tile; nor 24 inches when

strip flooring 2^2 inch thick is laid at right

angles to the joists.

If subfloors may be exposed to rain during construction, square-edged boards should be laid with

open joints for drainage, and tongued-and-grooved

boards should have holes at suitable intervals to

allow runoff of rainwater. If the house is of balloon frame construction, blocking should be installed between ends of joists at the walls as a

nailing base for the ends of diagonal subfloor

boards and also where subflooring is cut away for

plumbing, heating, or similar openings. A i/2-inch

clearance should be provided between the subfloor

and masonry or concrete walls.

Plywood

Subfloors may be 5-ply structural interior plywood if used where it is fully protected, as over a

heated basement, or 5-ply exterior plywood when

exposed to dampness, such as may occur in crawl

spaces. Plywood should be installed with the

outer plies at right angles with the joists and

with end joints meeting over joists.

Minimum plywood thicknesses and maximum

joist spacings as required by the Federal Housing

Administration are shown in table 6. Plywood

% inch thick may be used under ss^^-inch wood

strip flooring for a working surface or construction deck, provided the joists are spaced not over
14 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

16 inches on center, and the finish flooring is installed at right angles to the joists and nailed to

them.

Plywood subfloor should be nailed at each bearino- with eightpenny common nails or special types

(such as grooved nails) of comparable size spaced

6 inches on center along all edges and 10 inches

on center along intermediate bearing members.

A i/2-iiich clearance between the plywood subfloor

and masonry or concrete walls should be provided.

Occasionally the floor framing may be beams,

somewhat larger and spaced at greater intervals

than joists. When this occurs, the beams may be

covered with thick plywood, such as that designated 2-4—1 by the industry. The plywood then

serves the dual function of a structural floor and

a subfloor.

TABLE 6.—Minimum plywood subflooring thickness and

maximum joist spacing for Douglas-fir and western softwood plywoods

Minimum

thickness

Maximum joist

spacing (on center)

Plywood species

Wood

strip

flooring

Wood

block 1

Douglas-fir

Western softwoods

Inches

%

%

%

Inches

2 16

2 20

24

2 16

2 20

24

Inches

16

20

24

16

20

24

' Solid blocking is used under all plywood edges at right angles to joists Î May be 24 Inclies on center where ^Ha-inch strip floor is installed at right angles to the joist.

Plank

Plank subflooring is sometimes used over beam

framing in place of joists and boards, the plank

serving as a support for the finish floor. Plank

should be of nominal 2-inch material, with

tongued-and-grooved or splined edges and not over

8 inches wide. End joints should occur over a

support, and no two adjacent planks should have

joints over the same support.

Installation of the Finish Floor

Delivery and Storage of Flooring

The proper moisture content of flooring at time

of installation is an all-important factor in obtaining a satisfactory floor. The manufacturer

and dealer share the responsibility of providing

properly dried material, and it is necessary, for

best results, to use equal care to protect it from

moisture at the construction site.

Flooring should preferably not be delivered on

a damp or rainy day, unless fully protected. The

object is to prevent exposed boards and ends of

others in the bundles from absorbing moisture and

swelling. If the boards are laid in this condition

the excess moisture will later dry out, and the flooring will shrink and show cracks. Any flooring

inadvertently exposed to damp or wet conditions

should be redried before installation.

If wet plaster or masonry is to be used in the

home, it is preferable to wait until these are thoroughly dry before delivery and installation of the

flooring. This prevents absorption of moisture by

the flooring from the high humidities that prevail with moisture evaporation from the plaster

and cement.

Another condition that causes flooring to pick

up moisture during construction is less obvious but

more common. Between the time the floor is laid

and the house occupied, the general temperatures

within the house both day and night are likely

to be lower and the humidities higher than they

would be if the house were occupied. At thus

stage the house should be heated above outdoor

temperature, particularly at night, to keep the

relative humidity low enough to avoid absorption

of moisture by the wood.

In summary, five simple precautions should be

observed to keep flooring dry, particularly strip

and unit block types : ( 1 ) Do not truck or transfer

flooring in rain or snow; (2) do not store flooring

on the job outside of shelter or in a damp en- :

closure; (3) do not lay flooring when the building

is cold and damp ; wait until the plaster and ce- • ment work are thoroughly dry; (4) maintain a

temperature inside the house at least 15° F. above '''

outdoor temperatures during off-work periods and

do not let it cool below about 70° F. during the 26ir

summer or about 62° to 65° F. when the outdoor ^A

temperatures are below freezing (temperatures a

little higher will do no harm, but severe over- iitmm

heating should be avoided) ; and (5) with interior ifejuj

conditions controlled as above, open the bundles ;i|, f^

of flooring and pile it loosely in the building for i^,^

at least 4 days prior to laying so that it may come :^i¡g^

to equilibrium with conditions within the building. í(,,KIí,

Veneer tile flooring generally comes in moisture- I^KJ^

resistant packages that are not to be opened until ¿|j j

just before the flooring is laid. Other types m&J •:k^^

be similarly protected, and the manufacturers ^.^

instructions should be followed. i\^fr

Desirable Moisture Content ,'*iii

The recommended average moisture content for ^¡^^

flooring at time of laying is about 6 percent for the 1^^^^ ^ dry Southwestern States and about 7 percent

(hardwood) or 8 percent (softwood) for the majority of the rest of the United States (table 7

and fig. 5). Substantial deviation from the recommended values may be expected to result m

cracks between flooring boards if the initial moisture content is too high, or in buckled floors if the

«(

!%

lleL

m
WOOD FLOORS FOR DWELLINGS 15

// P£-/?C£NT

AVERAGE

MOISTURE CONTENT

FIGURE 5.—Recommended moisture content averages for interior flooring installed over wood joist for use in various

parts of the United States.

initial moisture content is too low. For floors

laid over concrete slabs, slightly higher moisture

contents are suitable, as indicated later.

Paper Over Subfloor

It is common practice to cover the subfloor with

. a deadening felt or heavy building paper, or both

(fig. 6). This felt or paper serves one or more of

several purposes. It will prevent dust from working up through the finish floor, acts as a sound

' deadener, reduces air infiltration from crawl spaces

, in basementless houses, retards moisture from rising through the floor from damp basements or

\ from the soil under basementless houses. Papers

! and felts will reduce air infiltration in crawl-space

houses, but this factor is relatively unimportant

where curtain walls are used around the crawl

space.

Moisture rising through the floor of basement-

( ' less houses has been assumed to be one important

Î: source of moisture in houses subject to cold weather

', condensation. While there may be some question

^ about this, a vapor-resistant paper would minimize

p this source of moisture. In general, paper or

!^ deadening felt appears unnecessary in one-story

; houses in mild climates, and the felt might be used

i^^ under the second floor only in two-story houses.

TABLE 7.—Recommended moisture content values for wood

flooring at time of installation

Location and type of flooring

Moisture content

(percent of weight of

ovendry wood)

Average ' Individual

pieces

Dry Southwestern States : ^

Softwood floorine

Percent

6

6

11

10

8

7

Percent

4-9

Hardwood ñoorinK _ 5-8

Damp Southern Coastal States: ^

Softwood flooring _ _ 8-13

Hardwood floorine 9-12

Remainder of United States: ^

Softwood floorine - - . 5-10

Hardwood floorine ._ 6-9

' If the average moisture content Is within ±1 percent of that recommended

and the moisture content values of all the pieces tested fall within the prescribed range, the entire lot will probably be satisfactory. To obtain a

realistic average, test at least 10 percent of each item.

' For limiting range, see figure i.

Since plywood subflooring acts as a wind and

dust stop, the principal purpose of using paper

would be to deaden sound. Paper or felt is not

generally used where resilient tile or wood floors

are laid m mastic.
16 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

FiGUBE 6.—Marking position of Joists on paper and felt for guidance in nailing. M100945F

Installing Strip Flooring

The flooring strips should be started square with

the room (fig. 7,Ä). Since, in modern house construction, thresholds are no longer used, all flooring is laid in one direction to avoid the unsightly

break that would occur at each opening if the

direction were varied in each room on the same

floor. Strip flooring should be laid crosswise to

the floor joists, and looks best when laid lengthwise in a rectangular room. Since joists generally

span the short way in a living room, that room establishes the direction for flooring in other rooms.

The first strip of flooring is placed parallel to

the wall with the tongue edge out and is face nailed

near the groove edge. The nails should be driven

into the joists and near enough to the edge of the

strip so that they will be covered by the shoe molding (fig. 7, B). Alternatively, the first strip of

flooring may be nailed through the tongue. Figure

7, C shows that the nail is driven in where the

tongue adjoins the shoulder and at an angle between 45° and 50°. The nail should not be driven

completely down with the hammer as the edge of

the flooring may be easily struck and damaged

(fig. 7, Z>). A nail set, in the position shown in

figure 7, Z>, should be used for the final driving.

Predrilling the holes through the tongue is sometimes necessary to avoid splitting the flooring, and

makes it easier to drive the nails into the joist.

Several types of nailing machines have been developed to facilitate the nailing of the various catterns of flooring. Some of these are mechanical

devices that use conventional nails and drop one

nail at a time into position to be driven into the

wood by a plunger that is struck with a hammer.

Other devices use special types of nails in which

the head is the same thickness as the shank and are

^

M

cat- '^,1

Mt

;;>t
WOOD FLOORS FOR DWELLINGS 17

STAGGER JOINTS IN ENDMATCHED FLOORING

BUILDING PAPER OR

DEADENING FELT

PLASTER

PLATE

GROUND

SUBFLOOR

— 5/g" CLEARANCE

WHEN FACE-NAILED AND SET

SHOE MOLD WILL COVER NAIL

FINISH

FLOOR

GREATER /

ANGLEDAMAGE

RESULTING FROM

HAMMER SETTING

\i

fei

{i

it

¥'

^:

NAIL SET

SUBELOOR

c D

I^GTiEE 7.—Application of strip flooring : A, General application ; B, laying first strip ; C, nailing method ; D, suggested

method for setting nails.

fastened together lightly into clips. These clips,

when installed in the machine (fig. 8), feed the

nails one at a time beneath a plunger that drives

the nail into the wood (fig. 9). The plunger can

be adjusted so that the head of the nail, either in

Wmd or face nailing, can be set below the surface

ofthewood(fig. 10).

For the second course of flooring, select the

pieces so that the butt joints will be well separated

from those in the first course. For floors to be

covered with rugs, the long lengths could be used

at the sides of the room and the short lengths in the

center where they will be covered. Each board

should be driven up snugly. To avoid crushing
18 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

FiGUEE 8.—Installing nail clips in floor nailing machine. M10094eF

the tongue with the hammer, a piece of scrap flooring should be used as a driving block. Slightly

crooked pieces may require wedging to force them

into alinement. Pieces with serious crook should

be rejected.

Floor squeaks are caused by the movement of

one board against another. Adequate nailing is

one important means of minimizing floor squeaks.

When possible, nail the finish floor through the

subñoor into the joist—it is much better than nailing the finish floor only into the subfloor. Various

types of nails are used in nailing various thicknesses of flooring. For 2%2-inch flooring, eightpenny steel cut flooring nails are recommended;

for 14-inch, sixpenny, and for %-inch, fourpenny

bright wire casing nails. All the foregoing are to

be blind-nailed at a uniform spacing not greater

than 10 inches.

For square-edge flooring, fi/g-inch barbed wire

flooring brads. No. 16, are recommended. This

style of flooring is face-nailed every 7 inches with

2 nails, one near each edge of the strip.

Other types of nails have been developed in recent year for nailing of flooring. These include

annularly grooved and the spirally grooved nails.

In using these nails, check the flooring manufacturer's recommendations as to size and spacing.

Installing Wood Block Flooring

The styles and types of wood block flooring vary

somewhat among manufacturers, so that no general installation procedure applicable to all can

be outlined. Rather, obtain detailed installation

instructions from the manufacturer whose product

is being used.

Block flooring may be installed on a wood subfloor either by mailing or by laying directly m

mastic (fig. 11 ). The adhesives and general methods of handling block flooring when bonding over

wood subfloors are similar to those described later

in the section on bonding wood flooring to concrete. As with strip flooring, an allowance for

expansion must be made with blocks of the unit

type made from short lengths of strip flooring.

With laminated blocks, however, less allowance for

expansion is needed.
WOOD FLOORS FOR DWELLINGS 19

FIGURE 9.—Installing hardwood strip flooring with nailing machine. M100947P
20 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

M100944P

FIGURE 10.—Hand setting nail below the surface of the

wood.

Mioosesp

FIGURE 11.—Block flooring laid directly in mastic on

plywood.

FLOORS OVER CONCRETE SLABS

A common type of floor construction for basementless houses is a concrete slab on the ground

over which wood flooring may be laid either in

mastic or on sleepers. To assure fully satisfactory

service, the slab must meet certain requirements

as to smoothness, drainage, dampproofing, and the

like.

Requirements for Slabs

The slab must meet certain basic requirements

to avoid difficulty with the finish floor. Principally, it must be level and smooth, laid over a

firm base, be dry, and be free from spalling and

dusting. A firm base of well-tamped subsoil, free

from roots, debris, and organic matter must be

provided ; this base should be covered with at least

4 inches of crushed rock or coarse gravel, well

tamped down. The gravel layer and a continuous

vapor barrier over it reduce materially the amount

of subsoil moisture that can come in contact with

the slab and perhaps work up through it. Suitable nonorganic moisture-resistive insulation

around the perimeter of the wall is necessary in

many climates to reduce heat loss and provide

comfortable floor temperature in cold weather.

Adequate drainage away from the walls is important to prevent surface moisture from entering

the floor.

Suitable details of construction for slab floors

of several types are shown in figures 12 to 16.

Another type, not illustrated, is the grade beam

and pier type. In this type, cylindrical concrete

piers are poured in holes bored into the subsoil.

Reinforced concrete beams, forming the perimeter

of the house, are located at grade and supported

on the piers and on the subsoil. The slab is poured

independently.

No specific guides exist for evaluating when the

slab is dry enough for installation of wood flooring. Generally, however, a period of 30 to 60

days of optimum drying conditions is considered

necessary, although conditions vary so greatly that

it is impossible to establish accurately the number

of days of drying required.

Without special equipment, a simple procedure

that may be expected to give a reasonable indication is as follows : Rubber or plastic sheets, at least

2 by 2 feet in size, are laid at several locations on

the surface of the slab and weighted to insure

uniform contact. If, after 24 hours, moisture appears on the underside of the sheet, the concrete

should be allowed to dry further before the flooring is installed.

Dampproofing of Slab

Figures 12 to 16 show a vapor barrier in contact

with the lower surface of the slab. This barrier

not only retards movement of water and vapor

from the soil upward through the slab, but also

prevents the flow of the concrete mix into the

porous layer beneath the slab.

Vapor barriers are essential for the proper performance of wood and other types of flooring installed on slabs on grade. Opinions differ consid-
WOOD FLOORS FOR DWELLINGS 21

SIDING

FLASHING

STARTING STRIP

FINISH GRADE'

ORIGINAL

GRADE

FINISH FLOORING

2"x 2" SLEEPER

METAL ANCHOR

REIN FORCEDCONCRETE SLAB

WIRE MESH

VAPOR BARRIER

GRAVEL FILL

HA .7'

>iJ'Jj-*f-REINFORCING RODS

FiGTJKE 12.—Combined slab and foundation. The gravel fill should be of a size that will be retained on a 1-inch mesh

screen.

SIDING

FLASHING

ASBESTOS-CEMENT

BOARD

FINISH GRADE

ORIGINAL GRADE

RIGID INSULATION

WATERPROOF AND

NONABSORPTIVE

FOOTINGFINISH FLOORING

2"y. 2"SLEEPER

REINFORCEDCONCRETE SLAB

WIRE MESH

VAPOR BARRIER

GRAVEL FILL

FiouEE 13.—Independent slab and foundation walls. In the method of construction shown, insulation is located at the

exterior surface of the wall. This method of installation may also be used on existing slab houses to minimize

cold floors. One method of laying the finish floor is shown. Sleepers shown are 2 by 2 wood members impregnated

with preservative and embedded in the concrete.
22 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

i-iosag

SEAL WITH I"

OF HOT TAR

FLASHING ^

FINISH GRADE-.

ORIGINAL GRADEFINISH FLOOR

REIN FORCEDCONCRETE SLAB

WIRE MESH

^^VAPOR BARRIER

GRAVEL FILL

riGUEE 14.—Concrete slab with foundation walls. Insulation is located around the exterior walls. Vapor barriers are

installed below the slab and on the warm side of the insulation, as shown. Insulation extends to within 1 inch of

top of floor slab, and the space above the insulation to the top of the slab is sealed off with hot tar.

TILE FLOOR

SEAL WITH I

OF HOT TAR

FLASHING

FINISH GRADE

ORIGINAL GRADE

WIRE MESH

CONCRETE SLAB

VAPOR BARRIER

GRAVEL FILL

RIGID INSULATION

AIR DUCT

VAPOR BARRIER

FiGUBE 15.—Independent concrete floor slab and foundation wall. Duct work located in slab around exterior wall. A

permanent type of vapor barrier is provided on both sides of insulation to stop soil moisture and to provide protection from cold weather condensation.
WOOD FLOORS FOR DWELLINGS 23

ANCHORED PLATE

FLOORING IN MASTIC

SEAL WITH I

OF HOT TAR

FLASHINGFINISH GRADE

WIRE MESH

<^'::yß^^P~cÖNCRETE SLAB

ORIGINAL GRADE

"^HOT-WATER

PIPES

3" INSUL A TING CONORETE

FiGUEE 16.—Independent concrete floor slab and concrete walls. Radiant-heating pipes are embedded in the floor.

erably as to whether the barrier should be at the

lower or the upper surface of the slab, each location having specific advantages and disadvantages.

Most commonly, it is placed below the slab.

For use below the slab, the barrier should have

not only good vapor resistance, but also resistance

to moisture and decay, and the ability to stand

rough handling. Two materials commonly used

are (1) smooth-surface 55-pound roll roofing,

laid with a 6-inch lap and with the lap sealed with

asphalt, and (2) three layers of roofer's felt, each

layer mopped with hot asphalt. Other materials

used as vapor barriers under slabs include heavygage polyethylene and polyethylene bonded to

kraft paper.

There is some question about the ability to provide a successful and permanent bond between the

slab and a barrier placed on top of it. However,

the wood ñooring industry reportedly has had

success in recent years with (1) two layers of 15-

pound asphalt-saturated felt laid in successive

coats of hot asphalt mastic, and (2) a 4-mil polyethylene film sandwiched between coats of a cold

asphalt mastic. Suitable types of polyethylene

film are available, and recommendations on this

point should be obtained from the flooring manufacturer.

The use of membranes over the slab is open to

question if the flooring is to be bonded with a

rigid adhesive designed to resist dimensional

changes (thereby placing high stresses in the bond

between flooring and base), or if the adhesive contains solvents likely to soften asphaltic compounds.

Cutback asphalt adhesives, however, are frequently used in bonding flooring over these membranes.

Moisture Content of Wood Flooring on

Concrete Slab

When wood flooring is placed in direct contact

with a concrete slab on grade, it is likely to have

a slightly higher moisture content than ordinarily

exists in wood frame construction. The average

moisture content of hardwood flooring on a slab

will be about 11 percent for the Southern Coastal

States and about 8 percent for the remainder of

the United States (compare table 7).

The procedures suggested earlier for insuring

proper moisture content at time of installation

should be followed for flooring to be installed on

slabs. These include thorough drying of concrete

and plaster, proper temperatures, opening of flooring bimdles when recommended, and the like.

Flooring Installed in Mastic

Long lengths of strip flooring are not ordinarily

laid directly in mastic. Where they are used in

special cases, or where short lengths are laid, as in

the herringbone pattern, standard patterns with

hollow backs may be selected. Special types of

strip flooring, however, are available as described

earlier (fig. 2).

In most unit blocks, the individual strips are not

tightly joined. These blocks have some advantage

over more rigid blocks in their ability to conform

to minor irregularities in the concrete surface. In

addition, any openings resulting from shrinkage

are distributed as a series of small cracks between

strips, rather than as fewer but larger ones between

blocks.
24 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

As with flooring laid on joists, provision must

be made for expansion of flooring laid in mastic.

With laminated blocks, particularly when laid in a

rigid adhesive, this is not so necessary because of

the much smaller dimensional change with

moisture.

Preparation of the Slab

Leveling.—Irregularities in the concrete surface

may require the use of leveling compounds to produce a suitable finished floor. Not all the usual

compounds are compatible with all the adhesives,

particularly because of possible deleterious effects

of solvents in the adhesive on the leveling compound ; this point should be checked with the flooring or adhesive manufacturer. Some also may

lack the adhesive strength to hold down all types

of flooring.

A mixture of latex and cement forming a rubberized compound may be used for leveling irregular concrete surfaces. It is strong and can

be applied in thin coats and to feather edges. The

mixture should not, however, be applied in thicknesses greater than 14 inch. It is suitable for use

over heated slabs.

Mixtures of emulsified asphalt, sand, and cement

are less expensive than the latex compounds. They

will, however, be softened by the solvents in certain types of adhesives, such as the rubber-base

adhesives described later. Underlayment compounds based on combinations of epoxy resins,

elastomers, cement, and sand are becoming available for use in leveling concrete floors where high

strength and resistance to solvent action are

required.

Various patching products, such as mixtures of

sand, gypsum, and cement, are manufactured.

These are generally low in strength and not suitable for leveling. They may be used to fill holes

in the slab.

Priming of surface.—After the concrete subfloor has been properly cured, dried, and any necessary leveling done, the floor should be well swept

and then a prime coat brush-applied over the entire slab at a coverage rate of 150 to 250 square feet

per gallon. With the cutback asphalt mastic

adhesives, the prime coat consists of a cutback

asphalt adhesive further reduced with a hydrocarbon solvent to a brushable consistency. Commercial priming solutions of this type are available. This type of primer should be applied at

least 24 hours prior to the application of the asphalt adhesive to insure that most of the solvent

has been removed. Dilute solutions of the asphalt

eniulsion adhesives are also available for use in

priming prior to the use of asphalt emulsion

adhesives.

It is the purpose of the primers to bond the

concrete "fines" to the base slab, to result in easier

troweling of the mastic, and to give Letter wetting

and adhesion of the mastic to the subñoor. Priming IS not generally required for use with the

rubber-base adhesives, but with some of the

rubber-base adhesives having a low-solids content,

two coats of adhesive, the first coat being essentially a prime coat, are applied to the concrete

slab to insure án adequate surface layer of adhesive. Only primers that are known to be compatible with the bonding adhesive or those primers

recommended by the adhesive manufacturer

should be used.

Asphalt priming of the concrete slab is also

used when vapor barriers are to be bonded over

the slab or when screeds are to be bonded on the

slab with asphalt adhesives.

Adequate! ventilation should always be provided

when using primers containing flammable solvents. No smoking or open flames, such as gas

pilot lights, should be permitted in the room while

the solvent concentration in the air is high.

Selection and Use of Mastic Adhesives

for Bonding Wood Flooring to Concrete

While the application of wood flooring over

concret« is usually done by mastic bonding, the

thicker types of strip flooring can also be applied

by nailing them to wood screeds or sleepers attached to the concrete subfloor.

The mastic adhesives used for this bonding of

wood flooring to concrete differ considerably from

the conventional woodworking adhesives in their

composition and properties. Exact classification

of mastic adhesives is difficult because of the many

asphalt, rubber, and resin compounds that are

combined to form these adhesives. These types

of mastic adhesives are usually less rigid and

produce joints of lower strength than do the

woodworking adhesives, and are formulated for

on-the-job application with little or no bonding pressure. Even within one general type

of mastic adhesive, the amounts and type of solvents and fillers used can greatly influence the

working characteristics of the adhesive. Therefore, when available, the manufacturer's instructions on the use of his adhesive should be closely

followed.

Information on the use of mastic adhesives

summarized here is intended for guidance purposes only, and is based primarily on information

obtained from brochures prepared by manufacturers of mastic adhesives and wood flooring.

The mastic adhesives currently known to be used

in bonding wood flooring to concrete can be

broadly classified into the following types:

I. Asphalt base.

1. Hot-melt.

2. Cutback.

3. Emulsion.

II. Rubber base.

1. Reclaimed, solvent-type.

2. Synthetic, solvent-type.

3. Emulsion.

III. Asphalt-rubber base.

IV. Miscellaneous special types.
WOOD FLOORS FOR DWELLINGS

TABLE 8.—Guide for selection of adhesive for bonding different types of wood flooring to concrete

25

Adhesive

Type of flooring

Hot-melt

asphalt '

Cutback

asphalt '

Emulsion

asphalt 1

Solventtype

reclaimed

rubber

Solventtype

synthetic

rubber

Latex

emulsion

Asphaltrubber

Wood strip (parquet) :

Restrained edges ^ ExcellentFair

ExcellentFair

ExcellentFair

Poor

ExcellentPoor

ExcellentPoor

ExcellentPoor

---do

Good 3---

Poor

Good3_--

Poor

Good 3

Poor

---do

Fair

---do

---do

---do

Good

---do

---do

Fair

Good

Fair

Good

Excellent-

---do

---do

Fair

Good 3 —

Fair

Good 3---

Excellent'

--.do 3

Fair

Fair.

TTnrpstrained edges ^ Good.

Unit block:

Restrained edges ^ _ - _ - Fair.

Unrestrained edges ^ ,

Laminated block (plywood) :

Restrained edges ^ - - -

Good.

Excellent.

Unrestrained edges ^ - Do.

VpDper Good.

> Not recommended for use with flooring having unrestrained edges, or

for use over radiant-heated slabs exceeding 85° F., because of low creepresisting properties of adhesives.

> Restrained edges—where the edges of adjacent strips or blocks are held

in alinement, as by splines or tongue-and-groove. Unrestrained edgesno provision for holding adjacent edges together as in square-edged strips

or blocks.

' These mastics cau be used with the thicker types of flooring providing

most of the moisture is removed from the mastic by using the proper assembly period, as outlined in the manufacturer's instructions.

The selection of the type of adhesive to be used

is largely dependent on the type and construction

of the flooring. General recommendations for selection are given in table 8.

For the thicker types of flooring, having

tongued-and-grooved or splined edges, which

maintain alinement between edges of adjacent

flooring pieces, and in which the entire flooring

section can act as a "floating section," one of the

asphalt mastics is usuallj^ recommended. These

adhesives flow slightly with continuously applied

stresses and have good rebonding characteristics.

For the thinner types of flooring, or for flooring

without splined edges such that each individual

piece must be well bonded, rubber-base adhesives

are usually recommended as having higher

strengths to retain the individual pieces in place.

Much of the information on the selection of the

type of mastic adhesive to be used is based on field

research or on observations of the working characteristics of the adhesives. Strength tests of small

test specimens have little practical value in deterinining the possible performance in a flooring

installation.

These mastic adhesives, in particular those of asphalt base, require that temperatures be at least

65° to 70° F. to obtain adequate bonding. This

temperature requirement applies to all materials,

the concrete slab, the wood flooring, the adhesive,

and the air above the slab.

Hot-Melt Asphalt Mastics

fu'^TT ^^^"''^ßlt mastics have been widely used in

the United States since 1890 in the bonding of

wood parquet flooring to concrete subfloors. The

early hot-melt mastics were made from either coaltar pitch or asphalt, while the hot-melt mastics

B

A

T c —

FIGURE 17.—Typical tooth pattern for trowel spreaders.

(Based on information supplied by adhesive and flooring manufacturers. )
26 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

currently being used in this country are mainly of

asphalt base. The refined native asphalts are

mixed with softer varieties of petroleum asphalt

to obtain an adhesive having the proper flow characteristics at both the temperature at which the

adhesive is applied and at room temperature service conditions.

The hot-melt asphalt mastics are usually heated

to a temperature of approximately 240° F. so that

they liquefy and can be applied with a notched

spreader to the concrete subñoors. This is frequently done by heating the pail or drum on an

open fire outside the house. The liquid mastic is

generally poured directly on the subfloor in limited quantities such as can be well troweled before

cooling. A typical trowel-tooth pattern used for

spreading a hot-melt mastic is shown in figure 17

and detailed in table 9. When such a trowel is

properly used, a gallon of hot-melt mastic should

cover 25 to 3.5 square feet of surface (table 9).

Sometimes, as an alternative to spreading, the

lower surface of the wood flooring is immersed

in the melted mastic.

After applying the hot mastic to the concrete

subfloor or flooring, the flooring is laid directly in

place. Some manufacturers supplying this type

of adhesive recommend waiting until the surface

of the mastic glazes over (15 minutes to several

hours, depending on the temperature and humidity

in the room) before laying the floor. However,

good results may generally be obtained even if

the mastic adhesive is allowed to "set" overnight

before the flooring pieces are laid in place.

When the wood flooring is laid in the hot-melt

mastics, it is not considered necessary to apply any

pressure other than a slight tap to bring the pieces

of flooring into their proper place. Walking over

the floor during use will embed the flooring into

the mastic.

This type of mastic is now generally recommended only for use with the grooved or splined

types of wood parquet block floor or for use with

the short lengths of tongued-and-grooved strip

flooring used in herringbone pattern flooring, although the early type floors in Europe having

square edges were bonded with good success with

this general type of adhesive. Laminated-block

floors can also be bonded with this type of adhesive,

but as the adhesive requirements for bonding the

laminated-block flooring to the subfloor are not so

restrictive, other types of adhesives, either cutback

or emulsions of asphalt or rubber, which are easier

to apply, are more widely used.

With the splined types of block or strip flooring, the asphalt mastic flows with any slow change

in dimensions of the flooring, and the entire floor

acts as a floating section with the edges of the individual pieces restrained from coming up by the

tongue-and-groove or splines. With the thinner

floors not having the tongue-and-grooves or

splines, or with square-edged flooring, asphalt adhesives in general, because of their plastic flow

nature, cannot for long restrain any tendencies of

the edges of the flooring to warp.

These unmodified asphalt mastic adhesives, because of their plastic flow characteristics, are not

generally recommended for use in floors containing radiant heat coils.

The hot-melt mastic adhesives have the following advantages, as compared to the cutback asphalt mastics described later: (1) They do not

contain flammable solvents that must be removed

into the atmosphere of the room; (2) they quickly

lose their fluid properties after spreading, and

therefore are not so likely to squeeze up between

the flooring boards during laying; (3) they have

a long record of successful use.

Cutback Asphalt Mastics

The cutback asphalt mastics, of the general type

formulated for use in the bonding of asphalt tile,

have been found satisfactory for bonding wood

flooring to "on and above grade" concrete slabs.

These cutback types are generally more convenient

to apply than the hot asphalt mastics. Cutback

asphalt mastics are usually formulated by reducing the hot-melt asphalt mastics with hydrocarbon

solvents. A small percentage of asbestos fibers.

TABLE 9.—Dimensions for adhesive trowel spreader and approximate flooT coverage

Adhesive

Trowel part 1 Approximate

coverage

A B C

per gallon *

Rot-melt asphalt. Inches

M to 3/8

K to Ms

Me

Yi to Me

Me

/4 to Ms

Inches

Me

Y2

Yi

Me to Yi

Me

Inches

M.

Me to M4

Ma to Yi

Me to Y,

Y% to Me

Me

Me to M

Square feet

25 to 35

Cutback asphalt _ _ 30 to 40

Emulsion asphalt 30 to 40

Solvent-type reclaimed rubber 45 to 60

Solvent-type synthetic rubber 45 to 60

Rubber emulsion 45 to 60

Cutback asphalt-rubber. 30 to 40

I Trowc4 parts iUustrated in flpurc 17.

Spreader to be inclined during use to obtain proper coverage For the

more viscous types of mastics, teeth may sometimes be of a rectangular shape

with a sUght reduction in size.
WOOD FLOORS FOR DWELLINGS 27

or sometimes ground cork, is added to some mixtures to stabilize them and to adjust the consistency

for better application.

The cutback asphalt mastics should be formulated with the proper asphalt materials and fillers

to result in a nonhardening mastic that will flow

and embed the flooring, and also permit the entire

section of flooring to act as a floating slab. On

the other hand, the mastic should be rigid enough

to hold down the edges of the flooring, to resist

any sudden stressing, and to prevent the adhesive

from squeezing up between the flooring strips or

blocks.

These cutback asphalt adhesives are not normally recommended for use over concrete slabs

containing radiant heat coils, but some manufacturers classifying their adhesives as cutback

asphalt will permit their use on splined wood

floors having a maximum temperature of 85° F.

Adhesives that are a combination of asphalt and

reclaimed rubber, described later, are generally

considered more suitable for use over radiant

heated slabs.

The cutback asphalt mastics should be applied

to the primed subfloor, using a trowel of the type

shown in figure 17, in amounts covering 30 to 40

square feet per gallon (table 9). Typical trowel

spreading of a mastic adhesive on a concrete subfloor is shown in figure 18. The spread mastic

should be air-dried for at least 2 hours before the

flooring is laid in place. With some mastics, installation may be safely delayed up to 72 hours

if necessary. A good test to determme the proper

minimum time for laying is to rub the fingers lightly over the ridges of the spread mastic. As soon

as the mastic has dried sufficiently so that it does

not adhere to the fingers, the flooring can be laid

and tapped lightly in place.

The flooring will become embedded in the mastic

during use. However, to improve the imiformity

of bonding, pressure may be applied immediately

after the floor is laid by rolling it with a feltcovered floor roller. Flooring that is laid too

soon after the adhesive is applied will slip excessively while being laid, and the mastic will be

squeezed up between flooring pieces.

FIGURE 18.—Troweling mastic adhesive on a concrete subfloor. M89018r
28 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

The use of short assembly periods could be the

cause for "snapping" sounds sometimes heard

when one walks over installations bonded with

these adhesives. When a short assembly period is

used, some of the wet adhesive is transferred to the

back'of the flooring piece. In certain areas, contact may not be obtained because of nonuniform

concrete surfaces, warped flooring pieces, or nonuniform adhesive spread, except when one walks

over the flooring. The two adhesive surfaces will

come in contact and rebond together momentarily,

but then break apart with a snapping sound.

This type of adhesive can be used for bonding

all the types of flooring that are conventionally

bonded with hot-melt asphalt adhesives. This adhesive also gives excellent performance in bonding

plywood-block flooring. Because of its low adhesive strength and high flow characteristics, it is

not normally recommended for the bonding of

square-edged or veneer types of flooring.

The cutback asphalt has the advantages of : (1)

being more convenient to apply and spread than

the hot-melt asphalt mastics; (2) being less sensitive to the air-drying period than the solvent-type

synthetic rubber-base mastics described later; (3)

solvents being less flammable than those used in

solvent-type rubber-base mastics ; (4) adhesive remaining plastic and having better rebonding

properties than do the rubber-base mastics.

Emulsion Asphalt Mastics

Asphalt mastics are also supplied as water emulsions, stabilized by either clay or alkaline chemicals. These mastics have properties similar to

those of the cutback asphalt mastics, except that a

longer open assembly must normally be used to insure that the water is removed from the adhesive

before the flooring is laid.

The asphalt mastic is applied to the primed concrete subfloor with a notched trowel (fig. 17) at

rates given in table 9 and then dried for 12 to 24

hours before the flooring is laid in place. The

remainder of the procedure is the same as that

used with the cutback asphalt mastics.

The emulsion asphalt mastics have the advantage, as compared to the cutback asphalt mastic, of

containing no flammable solvents that must escape

into the atmosphere of the room.

Their disadvantages are as follows: (1) Care

must be taken that the adhesive is not stored under

freezing conditions, which might deteriorate the

adhesive; (2) a long open assembly must be used

to remove moisture from the adhesive film; and

(3) asphalt emulsion mastics are generally considered to be less resistant to high moisture and

alkaline conditions than are the cutback asphalt

mastics.

Rubber-Base Mastics

Rubber-base mastics are also available for use

in bonding wood flooring to concrete (figs. 19, 20)

or plywood (fig. 21). The rubber-base mastics

generally have higher cohesive strength and show

less flow under stress (plasticity) than the asphalt

mastics, but generally require the use of shorter

assembly periods (time between spreading of mastic and laying of flooring), use more flammable

solvents (except for the emulsions), and have

poorer rebonding characteristics.

M100451P

FIGURE 19.—Laying veneer strip flooring in rubber-base

mastic on concrete. FIGURE 20.—Tapping veneer flooring in place in

on concrete floor.

M10046SF

mastic
WOOD FLOORS FOR DWELLINGS 29

M100967F

FiGDEE 21.—Tapping wood

block flooring firmly in

place in rubber-base mastic laid over plywood.

WwiS 4Êm-'

1

Solvent-type reclaimed rvM>er.—These mastics

are applied much the same as are the cutback as-_

phalt mastics, except that the adhesive spread may

be reduced to a coverage of 45 to 60 square feet per

gallon. Heavier spreads may be required if the

concrete subfloor is not smooth. The maximum

assembly period between spreading of the adhesive

and laying of the flooring should not normally exceed 15 minutes.

These adhesives, in contrast to the asphalt adhesives, require that sufficient pressure be applied

to the flooring to maintain adhesive contact until

the adhesive has gained sufficient strength to hold

the flooring down. Initial contact is usually sufficient. Rolling of the flooring with a heavy roller

IS a desirable method of obtaining proper adhesive

contact. Pressure can be applied by lightly hammermg the flooring with a rubber mallet to insure

contact at the corners and edges (figs. 20, 21).

it any of the comers of the flooring will not stay

in place after being lightly hammered, they should

be held clown overnight with weights.

These rubber-base mastics are much more rigid

(less plastic), once the solvents have been removed,

than are the asphalt mastics. It is, therefore, an

advantage to use this type of adhesive for boncling

thin veneer flooring Avithout tongues or grooves,

which tends to turn up at the edges. With long

strips of thicker flooring, however, stresses may

develop during seasonal changes that would be

great enough to rupture these more rigid adhesives. The bond is then permanently damaged,

as these adhesives do not have the good rebonding

properties of the asphalt mastics.

Some of the rubber-base mastics are reported

to be formulated to withstand temperatures up

to 140° F. without appreciable softening or deterioration, and therefore would normally give

better performance than the asphalt mastics for

bonding flooring to slabs in which radiant heating
30 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

tubes are embedded. Solvent-type rubber-base

adhesives contain more flammable solvents (open

cup flash point of less than 40° F.) than the cutback asphalt adhesives, and care must be taken

that there is sufficient ventilation to remove the

solvents and no possible source of ignition is in

the room.

Solvent-type synthetic ruhher.—Synthetic rubber-base mastics, usually with a butadiene-styrene

copolymer (GR-S) or neoprene base, have working characteristics similar to those of the reclaimed

rubber mastics, except that they usually have better "tack" properties and can be used with longer

open assembly j)eriods than the latter.

One of the solvent-type synthetic rubber mastics (believed to have a GR-S base) can be used

for bonding wood flooring to concrete by applying

the mastic to the concrete with a notched spreader

(fig. 17) to obtain a coverage of 45 to 60 square

feet per gallon (table 9). The flooring can then

be laid after a drying period of from 15 minutes

to ap^^roximately 1 hour. Good contact of the

flooring to the mastic adhesive should be obtained,

at least momentarily, during the first hour after

spreading, while the adhesive still has high "tack."

Pressure can be applied in the same manner as for

solvent-type reclaimed rubber mastics.

This type of adhesive gives good performance

in the bonding of thin veneer flooring or flooring

without tongued-and-grooved or splined edges because of its high initial tack and strength. Because of the high cost, however, the use of highly

flammable solvents, and relatively short assembly

period of the solvent-type synthetic rubber adhesives, the asphalt mastics are better suited for

bonding strip parquet, wood block, or laminated

block flooring, with tongued-and-grooved or

splined edges.

The "contact" cements, which are solvent-type

synthetic rubber (neoprene) mastics developed for

bonding high-pressure plastic laminates to counter

tops, have been found to give the best performance

of the various types of adhesives in bonding veneer

flooring to concrete. These adhesives must be applied to both the concrete subfloor and to the back

of the flooring pieces. A paint roller or a notched

spreader (fig. 17) can be used for spreading the

adhesive on the concrete surface.

With the more viscous types of these contact cements, which are the more suitable ones for this

type of bonding, the coverage should be about 65

square feet of flooring area per gallon (table 9),

half the adhesive being applied to the concrete and

the other to the back of the flooring pieces. If a

thinner type of "contact" cement is used, two coats

should be applied to each surface, with 1 hour of

air-drymg between coats. The adhesive should be

dried, following the final coat, for at least 20 minutes before the flooring is placed in contact with

it on tlie slab surface.

Care should tlien be taken that the flooring is

laid exactly m position, for no movement is possible because of the high "tack" of these adhesives.

Final pressure can be applied by forcing down the

flooring, with hand or foot, supplemented if necessary by tapping it with a rubber mallet (figs. 20,

21) or by rolling with a felt-covered floor roller.

The manufacturer's instructions should be followed regarding the maximum period between

spreading of the adhesive and the laying of the

flooring. Sometimes this waiting period can be

up to 16 hours, and even longer if a light wipe with

lacquer thinner or the application of mild heat

with an iron can be used.

Caution must be taken in using these solventtype synthetic rubber cements because many contain extremely flammable solvents (open cup flash

point less than 0° F.).

Rubber emulsions.—The rubber adhesives, including natural, reclaimed, and synthetic, are also

available as water emulsions or dispersions. These

emulsions, however, have not been so widely used

as the solvent types for bonding wood flooring to

concrete, primarily because of the water which

they might add to the wood flooring when used

with short assembly periods. The emulsions are

also generally regarded as not being so durable as

the solvent types, and applications of the emulsion

types, when used, have generally been limited to

bonding on dry "above grade" slabs. The principal advantages of the emulsion adhesives are

their lower cost and lack of flammability.

Asphalt-Rubber Mastics

Solvent-type cutback adhesives formulated from

a combination of asphalt and reclaimed rubber are •

available for bonding wood flooring to concrete.

These adhesives are excellent for bonding laminated block flooring to concrete and can also be

used, if properly formulated, to bond strip or wood

block flooring with or without splined edges.

These adhesives are reported to have greater

strength and rigidity and show better resistance to

heat than do the regular unmodified cutback asphalt adhesives. This type of adhesive can also

be used for bonding flooring to radiant-heated

slabs, provided the temperature at the bond will

not exceed 110° F.

The adhesive should be applied to concrete with

a notched spreader of the type shown in figure 17

to obtain a coverage of 30 to 40 square feet per

gallon (table 9). The wood flooring should then

be laid directly in place, normally within 20 minutes after the adhesive is spread, using a moderate

pressure obtainable in the same general manner as

for solvent-type reclaimed rubber mastics. The

principal disadvantages of this type of adhesive as

compared,to the cutback asphalt adhesives are the

shorter allowable assembly period, higher cost, and

poorer rebonding characteristics.

Miscellaneous Special Types of Adhesives

Several special types of flooring adhesives have

been used to a limited extent for bonding wood ,,^
WOOD FLOORS FOR DWELLINGS 31

flooring to concrete, including polyamidepoxy,

alcohol-soluble oleoresinous, and 2-part "chemical

set" latex adhesives. Their current use for this

purpose, however, has not been extensive enough

to indicate if any of these types have sufficient

advantages to result in wider usage in bonding of

wood flooring.

Floors Laid Over Sleepers

Where strip flooring is used over concrete slabs,

it should be laid over wood sleepers (screeds) attached to the slab. The sleepers may be embedded

in the concrete (fig. 13) although more commonly

they are laid in mastic or attached to the concrete

by clips (fig. 12). Sleepers should be pressure

treated with a suitable wood preservative. Creosote is not recommended, since it may stain the

finish floor if it bleeds through the nail holes. Alternatively, the sleepers may be heartwood of a

durable species.

Mastic bonding the sleepers to the concrete has

been widely used. Information on the method has

been supplied by the National Oak Flooring Manufacturers' Association. Essentially this method

consists, after proper installation and priming of

the concrete slab, of applying hot-melt or cutback

asphalt mastic to the surface of the slab with a

notched trowel (fig. 17) or by direct pouring to

result in a mastic depth of %2 to i/4 inch (25 square

feet per gallon). The mastic can be applied to

either the entire area of the floor, resulting m some

resistance to permeation of water vapor, or to

only the areas where the sleepers are to be placed.

Dry, flat 2- by 4-inch or 2- by 2-inch lumber

sleepers should then be immediately enibedded into

the mastic, before the adhesive gains initial "set."

The sleepers, in random lengths from 18 to 48

inches, are laid at right angles to the proposed direction of the final floor and in a series of staggered

rows, 12 inches on center as shown in figure 22, or

16 inches if a subfloor is used. The ends of the

individual sleepers should overlap each other 4

inches, and the sleeper ends should be at least 1

inch from the base plate. When the sleepers are

attached by anchors, generally full-length sleepers

are used.

The most common method of anchoring wood

sleepers is by means of sheetmetal strips embedded

in the concrete at intervals along the length. After

the sleeper has been wedged to the desired level

position, the projecting ends of the anchors are

folded over the sleeper and nailed to it. Anchor

bolts embedded in the hardened concrete may be

used, but the cost of installation is so high as to

be prohibitive. Power-driven fasteners may also

be used to fasten sleepers to the concrete. With

this type, a special nail is driven through the wood

into the concrete by means of a gun, the driving

power being supplied by a power cartridge. This

method eliminates the necessity for presetting clips

in the soft concrete at predetermined locations.

K ouBE 22.—Arrangement of mastic-bonded sleepers over concrete subfloor for use in installation of nailed strip flooring.
32

Installation of subfloor and finish floor is essentially the same as when they are installed over

joists. The flooring is laid at right angles to the

sleepers, and each strip should bear on at least two

sleepers. Flooring should be nailed to each

sleeper and where a strip passes over the lap between sleepers, it should be nailed to both.

Square-edge flooring should not be used.

Wood Floors Below Grade

Because of the difficulties that may be encountered when wood floors are exposed to condensation or prolonged high humidity, wood flooring

is generally not recommended for use at locations

below grade where such conditions may be expected. Basement areas are characteristically

cool, and the cooling of outside summer air as it

enters the basement increases the relative humidity

markedly as well as increasing the possibility of

condensation on cool surfaces, such as water pipes

and perhaps concrete walls and floors. Both will

result in swelling of a wood floor and perhaps in

its buckling. Beyond this, however, there is also

the possibility of decay from continued exposure to

U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

free water, such as might exist from condensation

on the lower surface of flooring in contact with the

concrete, or to extremely high humidities that

might exist in unventilated areas, such as that below flooring on sleepers.

Modern developments, however, tend to reduce

the hazard. Insulation of floor slabs reduces the

temperature loss. Effective vapor barriers reduce

the amount of moisture that can move from the

slab to the wood floor. Beyond this, dehumidification offers considerable opportunity for reducing

the overall relative humidity of basement areas

and thereby the chances for condensation. The

relative humidity level that can be maintained in

a basement area by a dehumidification unit will

depend, of course, upon the room volume and on

the capacity of the unit. In general, however,

substantial improvement over the usual basement

conditions may be expected.

Thus, much of the objection to the below-grade

use of wood floors may be eliminated. The homeowner anticipating such use, however, should consider carefully all the factors and insure that all

the construction features and other steps needed

to reduce the moisture problem have been included.

FINISHING AND MAINTAINING WOOD FLOORS

General Requirements

After laying a wood floor, four steps may be

needed to complete the finishing process, namely

sanding of the surface, application of a filler for

certain woods, application of a stain to unify the

color, and selection and application of the kind of

finish to be used. Whether fillers or stains are

needed depends on the species of wood used and

individual preference.

A careful sanding to provide a smooth surface

is essential for a good finish because any irregularities or roughness in the base surface will be

magnified by the finish, regardless of the type.

The production of a satisfactory surface requires

sanding in several steps with progressively finer

sandpaper, usually with a machine, unless the area

is small. Since the quality of the sanding job determines in large part the quality of the final

finish and since the techniques required are exacting, sanding should generally be done by a man

who specializes in such work.

A filler is required for woods with large pores,

such as oak, walnut, and teak, if a smooth coating

without depressions over the pores is desired.

Fillers come in either liquid or paste form (the

latter to be thinned before application) and either

transparent or colored according to the effect desired. Citre is required m applying the fillers;

otherwise the final finish may appear uneven and

smeared.

Stains are sometimes used to obtain a more

nearly uniform color pattern when the individual

boards vary too much in their natural color.

Various stains are available, generally named for

the woods they are to imitate. The stain should

be of a type, such as an oil-base stain, that will

not raise the grain of the wood. It should be remembered that stains penetrate wood to a trifling

depth only; the protective finish must be carefully maintained to prevent wearing through the

stained layer, since it is difficult to renew the stain

at worn spots in such a way as to match the color

of surrounding areas.

The great preference is for a finish that leaves

the wood floor as nearly natural in appearance as

possible. The transparent finishes now in common use are wood sealer, shellac, varnish, and,

less often, lacquer. Linseed and other oils once

commonly used have now largely been displaced

by wood sealers. All of them can give good service if good materials are properly applied and if

the finish is suitably maintained.

Wood sealers, now the most popular and widely

used finishes, penetrate the wood just enough to

avoid formation of a surface coating of appreciable thickness. Consequently, although more

frequent attention may be required than with a ^

coating, traffic areas can generally be patched .|

without going over the entire floor. \

Shellac, varnish, and lacquer form a distinct ^

coating over the wood and give a lustrous finish,

usually glossy. They are suitable where it is de- ,
WOOD FLOORS FOR DWELLINGS 33

sired to let the floors go as long as possible without attention other than regular sweeping or dry

mopping and where it is convenient to go to more

trouble when renewal is required. Such transparent coatings wear out in areas of highest traffic and, since it is generally not possible to do a

fully satisfactory job of patching the worn areas,

the flooring in a whole room or series of rooms

must be refinished. In addition, shellac waterspots readily, and lacquer is difficult to apply because it dries too quickly.

Opaque finishes, such as paints or enamels, are

seldom used in the interiors of homes. When

used, the labels should state specifically that they

are suitable for wood floors, since many paints are

not tough enough or sufficiently abrasion-resistant

to be suitable. The same is true of various

varnishes.

The durability of floor finishes can be improved

by keeping them waxed. Paste waxes generally

give the best appearance and durability, particularly if polished by machine. Water-emulsion

floor waxes require no polishing—they are merely

mopped on the floor and allowed to dry. While

commonly used, they give a somewhat less attractive and less durable wax finish than does a machine-polished paste wax.

Best maintenance practice requires at least partial refinishing as soon as the finish wears thin

in the traffic areas but before the wood has been

left unprotected. Within limits, even the transparent coating finishes can be renewed in spots one

or more times. Eventually, however, the old finish

must be removed entirely. This is best done by

power sanding, but may be done with varnish

removers or other materials, the technique depending upon the nature of the original finish.

Finely finished floors should never be scrubbed

with water. Sweeping or dry mopping should be

adequate for routine cleaning. Water, ink, or

other spots may offer some difficulty, but generally techniques are available for handling them

without complete removal and renewal of the finish

unless the penetration and extent of the spot are

too great.

Sanding

All finishes require the surface of wood flooring

to be made smooth by sanding or scraping just

before the first coat of finishing material is applied. Just as the finish brings out the full beauty

of the wood, it also reveals any defects or roughness left in the surface. Even irregularities that

can scarcely be seen before finishing become conspicuous afterward. Unless prefinished, flooring

usually has not been sanded by the manufacturer

and bears slight ridges left by the planer. Such

planer marks may seem unimportant at first but

will mar the appearance later on when the finish

m been applied. Moreover, if much time passes

oetween the finish sanding and the application of

nnish, some roughness may develop from raising

of the grain of the wood brought about by chang

ing moisture content. Floors therefore should be

sanded immediately before finishing is begun—ii

possible, the day when the first finish coat is to

be applied.

Sanding or scraping can, of course, be done by

hand, but that is usually far too laborious a method for areas of much size. Nevertheless, some

handwork may be necessary in places that are inaccessible to power machines. Most floor sanding

is done with electrically driven sanding machines.

The machine should be well designed, ruggedly

built, with its bearings well alined and kept in

good condition. A machine with badly worn

bearings may do more harm than good.

Floor sanding machines can often be rented at

retail paint or hardware stores or from concerns

that specialize in the renting of power equipment.

It should be pointed out, however, that sanding is

by far the most exacting step in floor finishing.

Nothing can be done later that will make up for

defects of a poor sanding job. It is therefore advisable, whenever possible, to have floors sanded

by a man who specializes in such work.

Sandpaper acts by gouging fine slivers from the

wood surface, leaving scratches, the size of which

is governed by the size of the grits on the paper.

Coarse grits act rapidly, but the scratches they

leave are conspicuous, especially if they cross the

grain of the wood. Fine grits act slowly, but, if

fine enough, the scratches left are too small to see.

Scratches are least noticeable when they run with

the grain of a wood with open texture (large

pores), such as oak. Scratches must be especially

fine to escape detection on a wood with close texture, such as maple, and must be still finer to remain unnoticed if they cross the grain of the wood.

In sanding a floor, time is saved by starting with

coarse sandpaper to remove the grosser roughness

and imperfections and to make the floor level as

quickly as possible. The scratches left by the

coarse grits are then removed by successive sandings, each one with a finer sandpaper than the one

before, until the scratches left by the last paper are

too small to be observed even after finish has been

applied.

Sanding Machines

Sanding machines are of two types, drum Sanders and disk sanders. In drum sanders (fig. 23)

the sandpaper is mounted on a cylindrical drum

that rotates on an axis parallel to the plane of the

floor and at right angles to the direction in which

the machine is moved. Thus the sandpaper makes

its scratches in straight lines in the direction of

movement of the machine. In disk sanders the

sandpaper is mounted on a disk that rotates in a

circle in the plane of the floor (fig. 24). As a disk

sander is moved over the floor, the grits make

spiral scratches that necessarily cross the grain

of the wood. The last sandpaper used with a disk

sander therefore may need to be a grade or two
34 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

MIOODSSF'

FIGURE 23.—Electrically driven drum type flooring sander.

finer than is necessary with a drum sander on a

floor in which all pieces run in the same direction.

A drum sander, however, cannot reach the last few

inches of floor nearest the baseboard. Electric

edgers, which are small disk sanders, are available

for sanding these edges of floor not reached by the

drum sanders (fig. 25).

Provision for varying the speed of rotation of

floor sanding machines is useful. If the speed is

too great, enough heat may be generated by friction to heat the wood to incipient charring temperatures and thereby produce dark marks called

burns, which can be removed only by sanding away

more wood than is otherwise necessary. On the

other hand, the operator wishes to use the highest

speed practicable to get the work done as rapidly

as possible. Burns can also be produced if the

machine is allowed to stand at one place while the

drum or disk is rotating.

Types of Sandpaper

Sandpaper, despite the name, is not made with

sand. The abrasive grits may be flint, garnet, or

emery, which are natural minerals, or the manufactured products aluminum oxide or silicon carbide. The backing may be paper, cloth, or a combmation of paper and cloth. Flint is the cheapest,

but wears out most rapidly and is seldom recommended for sanding machines. Garnet and aluminum oxide are most widely used for woodworking. Aluminura oxide is generally preferred for

high-speed iriuchines such as floor sanders. A few

M100466F

FIGURE 24.—Electrically driven disk type flooring sander.

professional floor men use silicon carbide. Paper

backing is satisfactory for floor sanding machines,

although combination paper and cloth backing

may be desirable for very coarse grits.

Each kind of sandpaper comes in a number of

grades according to the coarseness or fineness of

the grits. There are two systems of grading, by

arbitrary numbers that indicate the size of the

grits or by the number of meshes per inch in the

sieves through which the grits have been passed.

The customary grades are indicated in table 10.

The mark "3/0," for example, is a contraction for

the older way of writing "000," which in words is

referred to as "three ought." When both grit

number and mesh number are given, they may be

written "3/0(120)" or "3/0-120."

Sandpaper is sold in sheets 9 by 11 inches in size

for handwork, in pieces precut to sizes to fit any

one of the various models of drum sanders, and in

circular disks to fit the disk sanders. In ordering,

the make and model of the sanding machine should

be specified. Sandpaper is also sold in rolls 50

yards long and of various widths from which the

user may cut pieces with a suitable template to fit , ï

his sanding machine. There are also "thrift rolls" %

that are long enough to make 10 pieces for drum «Ï

sanders. '*

Sanding Procedure ¡i

The floor should be swept clean before begin- ^

ning the sanding. No water should be used. ^jj.

Newly laid hardwood floors should be traversed ^^,

with the sanding machine at least three times,first \,'
WOOD FLOORS FOR DWELLINGS 35

M100965F

FiGtTEE 25.—Small disk

ganders are used for

sanding the edges of floor

that are not reached by

« drum sanders.

m

îîf'l

with coarse sandpaper of grade No. 21/2-30 or

No. 2-36, then with medium paper of grade No.

1-50 or No. 1/2-6O, and finally with fine paper of

grade No. 0-80 or No. 2/0-100. Although acceptable results are sometimes obtained with only two

passes, three are generally recommended. For an

especially smooth finish, the third pass should be

made with No. 0-80 paper, followed by a fourth

pass with No. 2/0-100 paper, and even a fifth pass

with No. 3/0-120 paper.

Another method is to buff the hardwood floor

with steel wool of No. 1 coarseness after the third

pass with No. 0-80 sandpaper. Such buffing can

be done by machine, because there are available

rolls of steel wool that can be substituted for the

drum in drum sandei^s. Steel wool, however,

should not be used on oak floors unprotected by

finish, because minute particles of steel left in the

wood may later cause iron stains under certain

conditions.
36 U.S. DEPT. OF AGRICXJLTTJRE HANDBOOK NO. 2 04

TABLE 10.--Grading chart for sandpaper

Garnet, silicon Flint Emery

Type carbide, aluminum oxide

paper cloth

Very coarse 4^2-12

4-16

3^2-20

3-24 3/2

Coarse 2^2-30 3 3V_/ ^JÍAJÍ LJ^^_-^ — — — — — "—

2-36

2H m-io 2 2/2

IVTediuiii 1-50 1/2 iTA^-í*ü »_iü* ^- ^ — ^ — ^ .—

K2-6O

2

1 l'A

0-80

H

1

'A

Fine 2/0-100

0 0

3/0-120

2/0

4/0-150 2/0

5/0-180

3/0

3/0

Verv fine 6/0-220

7/0-240

4/0

5/0

^ \^i W ÍM Li^-t — — .— — — — — ^ — —

8/0-280

9/0-320

-360

10/0-400

-500

-600

Two traverses of the sanding machine usually

suffice for softwood floors. The first pass may be

made with No. 2-36 sandpaper and the second with

No. 1/2-60 sandpaper. Finer grades of sandpaper usually fail to improve the results appreciably.

On strip flooring or other patterns in which all

pieces lie with the grain in the same direction, it

is possible to operate drum sanders either with or

across the grain of the wood at will. It is then

helpful to make one of the earlier passes with the

coarse or medium sandpaper either across the

grain or at an angle of 45° to the wood grain.

Some authorities recommend that the pass across

the grain be made with the coarse paper, w-hereas

others prefer to make it wdth the medium paper.

All other passes should be made with the grain.

It is further helpful to make the two passes that

run with the wood grain from opposite directions.

Some floor men prefer a disk sander for the last

traverse, even when a drum sander is used for the

earlier passes.

On parquet or unit block flooring, it is necessary

to cross the grain of many of the pieces at each

traverse. Each pass may well be made in a different direction, say two at right angles to each

other and the third at 45° to the first two. Disk

sanders necessarily cross the vrood grain at each

pass. Extra care should be taken to see that each

traverse after the first is deep enough to remov-e

all scratches left by the previous pass, and the last

pass should be made with No. 2/0-100 or, if necessary, with No. 3/0-120 paper. Disk sanders are

sometimes preferred over drum sanders for parquet or unit block floors.

After each pass with a drum sander, an edger

should be used for the parts of the floor near the

edges that are not reached by the drum sander.

Even with a large disk sander, there may be places

at the corners where an edger may be used to advantage. If there are places inaccessible even to

an edger, such as places near radiator pipes, they

must be sanded or scraped by hand.

Before the sanding is considered complete, the

floor should be inspected carefully to see that all

blemishes have been removed, a smooth surface

produced, and all visible scratches removed. Defects can be seen most readily if the floor is viewed

against light at a low angle of incidence so that

any ridges will cast shadows. Remember that any

defects left at this time will show much more

prominently after finishing materials have been

applied.

When sanding has been completed, the floor

should be swept free from dust and may well be

wiped with a painter's tack-rag. The walls, windows, and doors also should be dusted to keep dust

motes from dropping into wet finishing materials

to mar their appearance. Application of finishing materials should begin promptly so that there

will be no time for changing moisture conditions

to raise the grain of the wood again.

When wood floors have once been finished and

the finish has worn out, it is usually expected that

the finish can be renewed without sanding the

floors again. Sometimes, however, floors become

scarred or discolored by accident or abuse or from

neglected maintenance to a point where sanding

again becomes necessary. Tlie sanding may then

begin with very coarse sandpaper. No. 4^16 or No.

3-24, to remove the old finish and blemishes. Two

passes should be made, each 45° to the direction of

the wood grain but at 90° to each other. From

that point the sanding should proceed in the same

way as has already been described for newly laid

flooring- Alternatively, the old finish may be removed with a nonaqueous (no water) varnish remover, after which the floor should be sanded as

for new flooring.

Staining

The usual preference on hardwood floors is for

a floor finish that leaves the wood as nearly in its

natural color as possible. All finishing materials,

however, even though entirely without color themselves, apparently deepen the natural color of

wood, for the same reason that wood always appears more richly colored when wet than when dry.

Deeply penetrating finishes, such as linseed oil and

the "floor oils" that were often used in former

times, deepen the wood color more than less penetrating finishes, such as wood sealers, shellac, and
WOOD FLOORS FOR DWELLINGS 37

lacquers. Of course, if the finishing material itself has considerable color, this color will be added

to the overall effect.

A further enrichment of the color of wood ñoors

comes with age. Light, even the subdued light

inside houses, slowly deepens and browns the very

thin superficial layer of the wood into which the

light penetrates, producing the patina so much

prized on old wood pieces. In addition, light and

oxygen gradually act on varnishes and wood sealers to form colored decomposition products. The

extent to which wood floors change in color with

age from these two processes depends both on the

kind of wood and the properties of the finishing

materials. Fortunately, the color changes are

usually of a pleasing nature.

When desired, the color of a hardwood floor

may be altered without obscuring the grain of the

wood by applying a wood stain of suitable color.

Floors laid with wood of the lower grades in which

there may be conspicuous variation in natural

color may be rendered more nearly uniform in appearance by use of fairly dark stain. The color

of wood stains is often indicated by naming them

for the wood on which they are to be used or whose

color they are to imitate, with further qualification for the shade or character of color. Thus

there are light oak, dark oak, walnut, red mahogany, brown mahogany wood stains, and others.

The stain should be an oil stain or at least a stain

made without water, such as that known as "nongrain-raising" stain.

No stain penetrates wood uniformly to more

than a trifling depth. For that reason the subsequent protective finish on stained floors must be

maintained with particular care. If it is not and

the surface is allowed to wear away at places of

greatest traíRc, unstained wood will be revealed to

mar the appearance. It is rarely possible to renew

the stain at worn spots in such a way as to match

the color of the unworn areas. Penetration of

stains is especially shallow in very hard woods of

close texture, such as maple. It may be slightly

deeper in birch and beech and still deeper in opentextured hardwoods, such as oak, walnut, and teak.

Although stains penetrate somewhat deeper

into softwood than into the hardwoods commonly

used for flooring, the softwoods do not take stains

well. The springwood, which is the softer, lighter

colored part of the grain, takes up more stain and

becomes more highly colored than the harder,

naturally darker colored part of the grain. Thus

there is a reversal of the natural color gradations

of softwoods that is generally considered unattractive.

Instead of using stain, color may be imparted

to wood later on during application of a wood

sealer. Suitable oil stain may be mixed with the

nrst coat of sealer, or wood sealers may be purchased that already contain the color.

Filling

Wood fillers may be used on floors made of hardwoods with pores larger than those in birch;

namely, oak, walnut, or teak. Filler is useless on

softwoods and on hardwoods with small pores,

such as maple or beech. The pores in birch are

large enough to take filler when it is desired to

accentuate the grain of the wood by making the

pores dark in color but the pores are small enough

to go without filler if darkening is not required.

Filler accomplishes one or both of two purposes. It plugs the voids in the wood surface

left by large pores to make the surface smooth and

level, and if colored it makes the pores show more

prominently. Fillers therefore are of two kinds,

natural fillers that are transparent and without

color, and colored fillers that are opaque and

usually dark brown to black in color. Colored

fillers are commonly named for the wood on which

they are considered especially appropriate, for

example, oak, walnut, cherry, or mahogany wood

filler. Fillers may be a liquid, ready for application, or a paste to be thinned with mineral spirits

or turpentine (paint thinners) before application.

The directions given by the manufacturer usually

should be followed. The paste is better for fine

work.

Filler is applied best with a 4-inch flat brush.

The first strokes should be across the grain of the

wood, then a light stroke with the grain. Care

should be taken not to cover too large an area at

once, because there is further work to be done before the filler has had time to dry. Soon after the

initial glossy "wet" appearance gives way to a

dull "dry" appearance, the excess filler must be

wiped off with burlap, excelsior, or other suitable

material. Wipe first across the grain to pack the

filler into the pores and then finish with a few

lighter strokes with the grain. Care in wiping

should be taken to see that all excess filler is removed; otherwise the finish may appear uneven

and smeared.

Filler usually should be allowed to dry for 24

hours before further finish is applied. However,

there are fast-drying fillers for which the manufacturer may indicate that less drying time is

sufficient.

Manufacturers of some wood sealers for floors

recommend that the application of filler be deferred until the first coat of sealer has been applied

and has dried. Others recommend that the usual

practice of filling before sealing be followed. Still

others say that filler may be omitted entirely even

on hardwoods with large pores when their sealers

are used. In general, it is practicable to dispense

with filling if the sealer is buffed with steel wool

before it has hardened, as is described later. But

when shellac, varnish, or lacquer is used for the

final finish, hardwoods with large pores should always be filled.
38 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

Choice of Final Finish

The transparent finishes now in common use for

floors are shellac, varnish, wood sealer, and, much

less frequently, lacquer. In former times floors

were often finished with linseed oil or with cheaper

floor oils obtained largely from petroleum, but

such finishes gradually m.ade wood very dark in

color and have now been entirely displaced by

wood sealers. . .

"Wood floors can be maintained in good condition

with any one of the available floor finishes if good

materials are applied properly and if maintenance

methods appropriate for each kind of finish and

for the degree of wear to which the floor is subjected are used. No type of finish can be said to

be superior in all respects, and none will long continue to give good service unless suitably maintained. The secret of good floors lies in thorough

understanding of the nature and limitations of the

particular kind of finish chosen and in carefully

following the appropriate maintenance program.

Choice of finish should be dictated primarily by

the appearance desired and the methods of maintenance considered most convenient.

If a highly glossy, lustrous finish is desired, the

choice may well be shellac, varnish, or lacquer.

Such materials form coatings over the wood surface a few thousandths of an inch thick. A more

natural appearance with less gloss and resinous

luster is obtained by the wood sealer finish. In

using sealers, a thin layer of wood at the surface

is saturated with the finishing material, and any

excess is wiped or buffed off so that no coating of

appreciable thickness is left on the wood surface.

Transparent Coatings

The coating finishes—shellac, varnish, and

lacquer—suit the needs of those people who wish

to let their floors go as long as possible without

attention other than regular sweeping or dry mopping and are willing to go to more trouble when

further maintenance finally becomes necessary.

When the finish eventually must be renewed, it is

usually necessary to refinish the entire room or, if

the flooring runs without break from room to room,

all flooring on a given story.

As a rule, limited areas of a floor receive a preponderance of wear from traffic. The finish wears

out in such traffic lanes, while other parts of the

floor remain unworn. It is seldom possible to renew coating finishes in the traffic channels alone

without having the edges of the patching show.

Moreover, after three or four renewals of a coating

finish, the areas of little or no traffic acquire an

unduly thick layer of finishing material, the older

parts of which have darkened with age, and will

no longer blend in color Avith the thinner coatings

on the traffic channels. It is then necessary to remove all tlie old finisli either with varnish remover

or by rôsanding tlie floors before a new finish of

uniform appearance can be applied.

Among the coating finishes, shellac has the merit

of drying so rapidly that a floor may be finished

or refinished and put back into service overnight.

Varnishes, even the quick-drying, require longer

intervals between coats and remain tender for some

time, so that the floor should be kept out of service

for several days, although with care light service

often may be permitted within a day after the last

coat has been applied. Landlords and some

painters are inclined to prefer shellac finish; the

owner-occupant is likely to prefer varnish or sealer

finish.

Varnish is more resistant than shellac to water

that may be spilled on a floor. Water or even prolonged exposure to high humidity turns shellac

white. Good varnish finishes are also tougher and

less easily scratched than shellac. Most varnishes

gradually darken with age, whereas shellac does

not.

Lacquer dries as rapidly as shellac, is as resistant to water as varnish, and seldom darkens

with age. The lacquers widely used on furniture

or on automobiles are made for application by

spray gun rather than by brush. Lacquers made

for brushing are more expensive and are still

rather difficult to apply evenly on large surfaces

such as floors. Moreover, lacquers contain much

less nonvolatile material than varnish, so that more

coats are required to make a finish comparable in

luster to that obtained with varnish. For such

reasons, lacquers are used much less than the other

finishes for floors.

Opaque Coatings

Opaque paint or enamel can be used to finish

wood floors when it is desired to hide the grain

of the wood entirely and perhaps to provide colors

that are not satisfactorily attainaole in transparent finishes. Hardwood floors inside buildings,

however, are seldom painted, because most users

prefer to take advantage of the natural beauty

of the wood. Softwoods are considered less attractive in appearance. In former times, when

softwoods were sometimes used for interior floors

of homes for economy, they were often painted.

Some commercial buildings still use painted softwood floors.

Floors exposed to the weather, such as porch

floors, are predominantly of softwoods and are

usually painted. None of the transparent finishes

resist weather well enough to last very long out

of doors. Good floor paint or enamel proves much

more durable.

Sealers

Sealer finishes require more frequent attention,

but the maintenance is simple and involves little

inconvenience. If all goes well, sealer finishes may

be maintained indefinitely without removing the

old finish. Since no more than enough material

to saturate the wood surface is applied, there is

no buildup of coating thickness on areas of little
WOOD FLOORS FOR DWELLINGS 39

wear, and traffic channels can be patched without

going over the entire floor. Wood sealer finishes

have gained especially vride use for wood floors

exposed to unusually heavy traffic, such as gymnasiums, schools, stores, offices, and public

buildings.

Application of Final Finish

Varnishes, lacquers, and wood sealers are made

for many different uses. Only products made

specifically for finishing floors should be used for

that purpose. Spar varnish made for surfaces

exposed to the weather may be too soft to withstand the abrasion of traffic, and cabinet finishing varnish made for furniture may lack the

toughness required for floors. It is best to use

floor varnish that is clearly so labeled by its manufacturer. So-called all-purpose varnish should

be used only if the label says specifically that it

is suitable for floor finishing. Similar caution

applies to lacquers and wood sealers.

Vamish Finish

The floor and room should be clean and as free

from dust as possible before varnishing begins.

Dust motes falling into wet varnish impair the

smoothness and appearance of the finish. The

room should be at 70° F. or somewhat warmer,

with plenty of fresh air. Varnish requires oxygen

from the air for its drying, and there should be

circulation to carry off the fumes of the volatile

thinners in the varnish. Damp weather may be

objectionable, since varnish dries slowly when the

air is very humid. It is well to test the drying

power of the varnish a day ahead of time by applying it on a nonabsorptive surface such as glass,

I metal, or well-primed wood.

fe Some varnishes lose their ability to dry

promptly after long storage on a dealer's shelf.

Poorly drying varnish can be exchanged for

fresher stock, or its drying properties may be restored by adding about a teaspoonful of paint

drier to a quart of varnish.

Vamish is applied with a wide brush. The

brush should be cleaned well before using. Parti-

^,j cles of old varnish or paint left in the brush may

work their way into the fresh varnish to mar the

, finish. Even a new brush may well be washed

^ with soap and water, shaken out, and dried before

:, using. First spread a brushful of vamish with

the grain of the wood, then stroke it across the

grain, and finally brush it lightly with the grain

again. Then go on to the next area with a fresh

> brushful. Do not go back to restroke areas that

¥ bave been covered previously.

At least 16 hours should elapse before the second coat of varnish is applied. Three coats will

:^ J« needed as a rule if the floor was not filled. If

■■ nUer was applied, two coats of vamish may suffice.

After the last coat of varnish, at least 24 hours,^

better 48 hours, should elapse before traffic is allowed on the floor. Varnish does not acquire its

full resistance to wear for several days.

Lacquer Finish

Lacquer is applied much like varnish except that

the work must be done more rapidly because lacquer dries so rapidly. The initial spreading, cross

brushing, and final stroking must be done very

quickly. Lacquer if brushed too long will not

level out with a smooth surface. Lacquer holds

its "wet edge" for a very limited time only. As

far as possible, the edges of brush strokes therefore

should coincide with the edges of boards in the

floor, and the beginning of a second brushful must

be joined to the end of the previous one very

promptly. With lacquer, an hour or two between

coats may be enough. The manufacturer's directions should indicate the required time.

Shellac Finish

Shellac for floors should be purchased in the

form of 5-pound cut shellac varnish, that is, 5

pounds of shellac resin in 1 gallon of alcohol. It

should be pure shellac varnish, unadulterated with

cheaper resins. The bleached shellac, commonly

called white shellac, is preferred for its pale color.

Orange shellac imparts far too much color. Always test shellac varnish to see that it dries

promptly without tackiness before applying it on

a floor. When stored too long, white shellac varnish loses its ability to dry hard as a result of

chemical reaction between the resin and the alcohol.

Shellac should be sold either in glass containers

or in metal containers that are lined with lead or

other coating to keep the varnish away from iron.

Shellac varnish contaminated with iron may produce black stains on woods that contain tannins,

such as oak.

The correct thinner for shellac varnish is 188-

proof No. 1 denatured alcohol. For application,

5-pound cut shellac varnish should be thinned

with 1 quart of alcohol per gallon. It should be

applied with a wide brush that will cover three

boards of strip flooring at a stroke and with long,

even strokes, taking care to joint the laps quickly

and smoothly.

The first coat on bare wood requires 15 to 20

minutes to dry. It should then be rubbed lightly

with fine steel wool or sandpaper and the floor

swept clean. A second coat should be applied, allowed to dry 2 to 3 hours, and then gone over

with steel wool or sandpaper, swept, and a third

coat applied. If possible, the floor should not be

put back into service until the next morning, but

if necessary, it may be walked on carefully about 'S

hours after finishing.
U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 2 04

FIGURE 26.—Applying sealer to hardwood floor. M100957F

If wax is to be used, it should not be applied less

than 8 hours after the last coat of shellac. Paste

wax is suitable. Water-emulsion wax should be

avoided because water may turn shellac white.

Floor Sealer

Manufacturers' directions for applying floor

sealer vary widely and sometimes are very inadequate. In general, floor sealers may be brushed

on with a wide brush or mopped on with a squeegee

or lamb's wool applicator, working first across the

grain of the wood and then smoothing out in the

direction of the grain (fig. 26). After an interval

of 15 minutes to an hour, according to the characteristics of the sealer, the excess is wiped off

with clean rags or a rubber squeegee. For best

results, the floor should then be buffed with No.

2 steel wool, although í^he Vjuffing may be omitted

by those who are willing to sacrifice something in

appearance and service. (On oak floors, presence

of the sealer makes it unlikely that any particles

of steel wool will become embedded in the surface

as previously mentioned for bare floors.)

If possible, the buffing should be done by a

rugged power-driven machine designed for buffing with steel wool. The next best procedure is

buffing with pads of steel wool attached to the

bottom of a sanding machine. Buffing may be

done by hand if no machine is available. One

coat of sealer may suffice if it is applied very

carefully, but a second coat is generally recommended for floors that have just been sanded. The

floor should be swept clean before making the

second application. . . A correct interval of time between application

of sealer and buffing is very important. If the

interval is too short, the sealer may still be too

fluid to buff properly. If it is too long, the excess

k... -,
WOOD FLOORS FOR DWELLINGS 41

sealer "gums" the steel wool badly, is removed

from the floor with diíRculty, and where not removed becomes blackened with detritus from the

steel wool. If the manufacturer of the sealer does

not specify the correct interval clearly, the user

should determine it for himself by trial on samples

of flooring or in some inconspicuous places where

imperfect results will not prove too disappointing.

Once the user has learned how to work successfully with one brand of sealer, he will do well to

continue using that brand, since he might have

to learn the technique all over again with another

brand.

Floor sealers are now offered by a number of

manufacturers of floor finishing materials and

equipment, who are usually able to give precise

and reliable instructions for the proper application and maintenance of their products. Sealers

are also sold by most of the larger paint and varnish manufacturers, although the preference of

their dealers is usually for floor varnishes.

Waxing Floors

Waxing of floors is done to best advantage with

paste floor wax and an electric polisliing machine

designed for the purpose. For best appearance

and durability there is no satisfactory substitute for the polishing machine ; polishing by hand

is far too laborious for the modern household and

too expensive for the business building. The

paste wax is mopped on the floor, allowed to stand

until the volatile thinner evaporates, which may

take 15 to 30 minutes, and the floor is then polished

with the machine.

The most modern type of floor waxing machine

applies the wax and polishes in the same operation. For those who wish to get along without a

polishing machine and are willing to accept a

somewhat less attractive and less durable wax

finish, there are water-emulsion floor waxes that

are merely mopped on the floor and allowed to

dry.

Floor Paint or Floor Enamel

Paint or enamel for use on wood floors should

be made especially for such use. The wear of

traffic requires paint that is hard enough to withstand abrasion and yet tough enough to withstand

impact. Paints or enamels made for other purposes may not have such properties in sufficient

. degree. The manufacturer's label should say

clearly that the product is intended for use on

I wood floors. Paints made for concrete floors may

!> serve also for wood, but there is no assurance

V that they will unless the label so states. For porch

|, floors exposed to the weather the label should also

i state clearly that the paint or enamel is suitable

tor exterior use.

On new floors or floors just sanded, at least two

coats ot floor pamt or enamel are necessary. The

nrst coat should be thinned moderately with paint

thinner in accordance with the manufacturer s directions. Subsequent coats usually should be applied unthinned. Each coat should stand at least

16 hours for drying before the next coat is applied or before the floor is opened to traflic.

Porch floors should be painted in warm, dry

weather.

It is generally necessary to repaint the entire

floor when the coating becomes worn through at

the traffic cliannels. Freshly applied paint, even

from the same lot as the original paint, does not

present the same appearance as the older paint.

After a few repaintings, the coating tends to become too thick on the areas of least wear and may

begin to crack and scale at the thick places. To

postpone such condition as long as possible, apply a first coat of new paint in the worn parts of

the traffic cliannels only and then apply a single

finish coat over the entire floor, brushing it out

as thin as practicable on the areas that receive

little wear. Once the coating begins to crack and

scale badly, it becomes necessary to remove all

the old coatings by sanding or with paint remover

so that the painting can be started over again with

a coating af even thickness.

Cracks in Floors

When floors are laid originally with insufficient

regard for control of moisture content, they may

present a problem of cracks or gaps between boards

by the time refinishing is in order. There is no

satisfactory way of eliminating such cracks short

of taking up the floor and relaying it.

Cracks open wider in winter when the wood

reaches a minimum moisture content and become

narrower in summer when the wood is more moist.

If the cracks are filled with a soft putty or crack

filler in winter, some of the filler may be squeezed

out during the following summer to be tracked

over the floor. If a hard filler is used, the wood

may be further compressed during the summer.

In either situation the cracks will open again during the next winter and may become worse than

they were before the filler was applied. Filler

applied in the summer will be insufficient to fill

the gaps when they become wider again in the

winter. On the whole, when cracks develop it

is best to learn to put up with them unless they are

bad enough to justify relayin; the floor.

Wide cracks, of course, tenc. to collect dust and

dirt. If they become completely filled with foreign matter, the cracks may no longer widen and

narrow with seasonal change in moisture in the

wood. As a result the cracks may become wider,

just as though they had been filled with a hard

filler. Regular use of a vacuum cleaner in normal

house cleaning should serve to keep the cracks

open. If necessary, compacted dirt may be pried

loose with a blunt instrument. For much the same

reason, floors with wide cracks, into which some

finishing material is bound to flow, are refinished
42 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

to best advantage in the late summer season when

the cracks are at their narrowest. When oak floors

with wide cracks are buffed with steel wool in refinishing, it is well to use a vacuum cleaner a few

days later to remove any particles of steel wool

from the cracks.

Refinishing Floors

Best maintenance requires at least partial refinishing as soon as the finish wears thin in the

traffic channels but before the wood has been left

unprotected there. If the floor has been waxed,

it is necessary to remove the wax before new

finish is applied because wax interferes with the

drying and adhesion of new finish. Most of the

wax should be scrubbed off with rags kept

moistened with turpentine or other paint thinner. The rest of the wax should be washed off

with soap and warm water, doing the work as

rapidly as possible so that the water will have too

little time to reach the wood or to turn a shellac

coating white. After the surface has dried again,

new finish may be applied.

With wood sealer finish no more may be necessary than to mop fresh sealer on the worn areas

of the traffic channels, wipe up any excess, and buff

the surface as has already been described for the

last coat on new floors. With the coating finishes,

varnish, lacquer, or shellac, two coats may be advisable on the worn areas but would be altogether

too much on the areas of little wear. It may therefore be practicable to apply a first coat in the worn

areas only, ending all brush strokes at joints between boards, and then to apply a second coat over

the entire floor.

After varnish, lacquer, or shellac finish has been

renewed several times, it may no longer be possible to refinish the worn areas to match the appearance of the unworn areas where too much old

finish discolored by age remains. It is then time

to remove the old finish entirely.

The best way to remove old finish is by power

sanding, which is necessary if the wood has become

badly scuffed or marred. But there is a limit to

the number of times a floor may be sanded because

each sanding removes a substantial amount of

wood as Sander dust. Other methods of removing

old finish therefore may be needed at times.

Floors OriginaUy Finished With OÜ

An old linseed oil finish embedded in the wood

may cause some difficulty. If a steel-wool buffing

machine is available, an attempt should first be

made to clean the floor sufficiently merely by buffing with No. 3 steel wool. If this is not feasible

or proves ineffective, a chemical treatment will

be necessary. Mild alkalies change oil and many

sealers or varnishes into soap that can be scrubbed

off witb^ water. The alkali used may be a water

solution of trisodium phosphate, washing soda or

a commercial cleanser. Lye is inadvisable because

it is strong enough to discolor some woods or even

to swell and soften them. Since alkaline solutions

are hard on the hands, rubber gloves should be

worn while using them.

In applying the alkali, flush a small area of the

floor at a time with the solution and allow it to

stand for a few minutes, then scrub with a stiff

brush or No. 1 steel wool. Next flush the area with

clean water and scrub to remove the soap that has

been formed, and finally remove all the water possible by mopping and let the floor dry thoroughly.

If the floor turns gray in color as a result of the

action of the alkali and water, bleach it with a

saturated solution of oxalic acid in water (oxalic

acid is poisonous and must be handled with care).

Einse off' the oxalic acid thoroughly with clean

water, mop, and let the floor dry completely. Any

raised grain or roughening of the surface of the

boards should be smoothed with sandpaper or steel ' }

wool before new finish is applied. '^

Floors Originally Finished With Varnish or Lacqu« '¡¡

Old varnish or lacquer can be removed with '^

liquid varnish remover. The remover should be

one made with organic liquids and should contain :•

no water. The directions for using the liquid re- ''

mover should be followed closely. f

If the first coat of the original varnish was !?,

thinned too much and penetrated into the wood '*'

too far, some of it may still remain embedded. It . will not interfere with the new finish except for "'

the darker color it produces. If the color is un- ^

acceptable, it may be possible to remove the em- -^

bedded varnish by the treatment with alkali de- ^

scribed for floors originally finished with oil. ''

m

Floors Originally Finished With Shellac M

Old shellac finish can be removed by scouring ^

the floor with No. 3 steel wool and denatured al- ^

cohol diluted half and half with water. If the ^

floor boards are level and are not warped or fj

cupped, the scouring can be done to advantage i

with a floor-polishing machine fitted with a wire i

brush to which a pad of No. 3 steel wool is at- '^

tached. After the scouring, the floor should be ''k

rinsed with a minimum amount of clean water and 'tij

allowed to dry thoroughly before refinishing with 'ISj

shellac. ' When white spots have developed in shellac finish from accidental contact with water, they may k\

often be taken out by rubbing lightly with a soft %

cloth moistened with denatured alcohol diluted J|

half and half with water. The alcohol, however, ^

must be used with care to avoid cutting the shellac ií,,,

coating. \

Floor Maintenance

Specific rules for the frequency of maintenance

of floor finishes cannot be set forth, because the V|,,

determining factor is the amount and kind of ,,:

traffic, which varies greatly. In many homes so .^^

much of the flooring is covered by rugs or carpets ^
WOOD FLOORS FOR DWELLINGS 43

that there may be no appreciable wear on the floor

finish except perhaps near doors between rooms.

Finish wears especially rapidly on bare floors near

doors to the exterior where water may be tracked

in during wet weather and those entering may

have gritty footwear. Foot mats near exterior

doors, of course, can be helpful in reducing the

wear on floor finishes from such sources.

The kind of footwear worn by the occupants

and their habits of walking also affect the wear on

floor finishes. Soft-soled footwear causes little or

no wear unless it is wet or gritty. On the other

hand, leather heels nailed in place and used on concrete sidewalks until the nailheads project seriously impair the durability of floor finishes and

may even scratch wood badly enough to require

resanding the floor. The small heels on women's

high-heeled shoes, which concentrate the load on

a small area, may be especially damaging.

The durability of floor finishes can be improved

by keeping them waxed. In homes, renewal of the

wax every 4 to 6 months may suffice, but more

frequent renewal may be necessary where traffic

is heavier. Well-waxed floors are easier to keep

clean by dry mopping. Wax over coating finishes

tends to make floors slippery unless the wax layer

is kept very thin. Over sealer finishes, wax is usually less slippery. Some floor waxes are made with

special ingredients to improve their resistance to

slip.

Floor finishes in gymnasiums, schoolrooms, and

commercial or public buildings are subjected to

much more severe service, as a rule, than are floors

in homes. Accordingly inspection and maintenance must be more regular and more frequent.

Some makers of floor fijiishing materials and

equipment will train a maintenance man for their

customers in the methods of keeping floors in good

condition. Sealer finishes applied and maintained

adequately with electric buffing machines have

proved especially satisfactory for heavy-duty

floors. Although frequent attention is required,

the work can be done in a few hours at night or

on weekends without interrupting the normal use

of the floor.

Use of gymnasium floors can usually be restricted to persons in shoes soled with rubber or

other nonabrasive footwear. Fast action in such

games as basketball produces sharp friction between footwear and floor finish that tends to produce "rubber burns" that mark some finishes more

seriously than others. Special sealers that resist

such marring especially well are made for gymnasium floors. If rubber burns are not too severe,

they can be removed by scrubbing with naphtha

or paint thinner.

Wood floors with fine finishes should never be

scrubbed with water or unnecessarily brought in

contact with water except in connection with rehmshmg old floors as already described. Sweeping or dry mopping should be all that is necessary

lor routme cleaning.

A soft cotton floor mop kept barely dampened

with a mixture of 3 parts of kerosene and 1 part

of paraffin oil is excellent for dry mopping. Commercial preparations are available for the purpose

also. When the mop becomes dirty, it should be

washed in hot water and soap, dried, and again

dampened with the mixture of kerosene and paraffin oil. Exceptional patches of dirt that cannot

be removed in this way, or rubber burns from

friction between rubber footwear and floor, may

be removed by rubbing lightly with fine steel wool

moistened with turpentine or paint thinner.

Badly soiled spots, such as gray spots where

water or pets' urine has been allowed to stand on

the floor for a time, may offer difficulty. Where

the finish is a floor sealer, the stained area can be

sanded by hand, patched with fresh sealer, and

buffed with a pad of steel wool. Similar patching

with varnish, lacquer, or shellac may not blend

perfectly with the rest of the floor but will usually

prove much less objectionable than the stain.

Where the water stain has penetrated the wood

too deeply to be removed by hand sanding, it is

necessary to remove the finish by sanding and

then to bleach the wood with oxalic acid as described for floors originally finished with oil.

Stains from some writing inks also can be

bleached with oxalic acid or with other commercial

wood bleaches, such as alkaline hydrogen peroxide

bleaches. Stains from vegetable oils or greases

usually will yield to the treatment with alkali

described for old oil finishes, but petroleum oils

or greases that become embedded in the wood may

resist all practicable treatments except that of

sanding off all the stained wood.

Varnish coatings and other finishes are not

effective in preventing long-term moisture changes

such as occur seasonally. They do, however, retard the entrance and exit of water and thus may

be expected to moderate the effects of short-term

changes, such as water spillage or short periods

of extremely high humidity. It is desirable,

therefore, to refinish worn areas as promptly as

possible to reduce the possibility of excessive

swelling, and perhaps buckling, from short-term

effects such as those mentioned.

Eliminating Squeaks in Floors

Floor squeaks are caused by relative movement

of the tongue of one flooring strip in the groove of

its neighbor. Such movement may occur for any

one of a number of reasons. For example, if the

floor joists are somewhat small for the span, they

may deflect sufficiently to permit movement in the

flooring. Similarly, if sleepers are not held down

tightly to a concrete slab, or come loose in service,

enough movement may be possible to cause squeaks.

Poorly manufactured flooring in which the

tongues are undersize and thus do not fit tightly

in the grooves may also lead to squeaks. Warped

flooring or subñooring may permit the boards to
44 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 204

rock under traffic; this is unlikely to be a factor

with hollow-back flooring. An unusual case,

which might occur occasionally, is one where the

joists change direction in adjoining rooms while

the flooring direction is constant. Where this

occurs, the flooring in one room would be parallel

to the'joists and deflection of the subfloor might

permit sufficient movement to cause squeaks.

Finally, and perhaps most commonly, squeaks may

result from inadequate nailing.

Obviously, the best method of eliminating flooring squeaks is to install well-made flooring on a

sound floor system, taking particular care in installation, especially with the nailing. If, however, squeaks do occur in a finished floor, a number

ofsteps may be taken.

First, determine the cause of movement so that

proper steps may be taken for correction. Regardless of cause, one expedient is to lubricate the

tongue with mineral oil introduced into the opening between adjacent boards. The oil must be

used sparingly, however ; too much may result in

stains in the flooring.

A fairly common and effective procedure is to

drive a nail through the face of the flooring into

the subfloor—preferably also into a joist. The

nail should be driven near the tongue edge of the

flooring strip, then set and the hole filled.

Where flooring is warped and the under surface

of the floor is exposed, screws through the subfloor

and into the finish floor will be effective in reducing

movement. This procedure will be somewhat less

objectionable than face nailing from the standpoint of appearance.

When the flooring strips run parallel to the

joists, as described earlier, little can be done if

there is a finished ceiling below the floor. Where

it is open, however, as in a garage or basement,

solid blocking may be fitted between and nailed

to the joists and snugly fitted against the subfloor.

The blocking needs to be at sufficiently close intervals to provide support for the subfloor and finish

floor. Adequate nailing to the joists is necessary

so that the blocking will maintain its position.

Experimental Flooring Types

In addition to the more usual types of wood

flooring described earlier, many attempts have

been made to develop types which have special

properties or which use lesser amounts of the highgrade material generally most in demand because

of its good appearance. The Forest Products

Laboratory has been active in this field and a few

of its experimental floors are described below.

The stabilized veneer tiles described earlier represent one method of using this type of material.

Experimental floors using strips rather than

squares of this material have given good results

when proper laying procedures were used.

Attempts to minimize the amount of high-grade

material are well illustrated by a veneer-lumber

flooring developed by the Forest Products Laboratory. It consists of a Yg-inch. layer of high-grade

veneer glued to a %-inch lumber backing, with the

grain of the two at right angles. The backing

lumber may be of any species denser than 25

pounds per cubic foot and may contain knots,

checks, splits, and other defects, so long as there

is an essentially sound surface adjacent to the face

veneer. After the two components are glued together, the backing is grooved parallel to its grain

at 1-inch intervals with the grooves extending almost through the backing. The cross-laminated

construction provides considerable dimensional

stability, and the grooving provides flexibility,

permitting installation over somewhat uneven

surfaces.

The unit block flooring described earlier generally consists of short tongued-and-grooved strips

held together by splines. A Laboratory-developed flooring eliminates not only the tongue-andgroove, but also the dressing of the edges of the

individual pieces. Random-width strips are assembled edge to edge and wood or hardboard

splines glued into the end-grain edges of the assembly. The improvement in utilization is obvious, since random-width strips are used, and the

dressing and matching are eliminated. The roughsawed edges have proved preferable to planed

edges, since they allows more room for expansion.

Resin-impregnated paper has been glued to the

surface of wood and plywood to impart improved

properties. Some high-density types of overlays

have been used experimentally on plywood for

flooring. The major improvement attained with

them has been to impart a hard, abrasion-resistant,

highly decorative wearing surface to softwood

plywood, which w'ould otherwise not be suitable

for finish flooring.

Wood has been modified in various ways to improve its dimensional stability and other properties. One such material, termed staypak, is

made by compressing wood under optimum conditions of moisture content and temperature. An

experimental floor of this material has given good

results over a period of several years.

O