United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL-RP-494

Controlling Decay in

Waterfront Structures

Evaluation, Prevention, and

Remedial Treatments

Terry L. Highley

Theodore Scheffer
Abstract Note

Decay in waterfront structures results in expensive repair or replacement of the damaged components. This

manual describes the problems caused by decay and

ways to avoid or control decay. The information presented is directed toward personnel who inspect and

maintain waterfront structures. The manual describes

(1) types of deterioration and underlying causes,

(2) construction practices that contribute to decay,

(3) decay detection, and (4) decay prevention, including remedial measures for decayed structures.

Keywords: Wood decay, waterfront structures, wood

maintenance, wood inspection

September 1989

Highley, Terry L.; Schaeffer, Theodore. 1989. Controlling decay

in waterfront structures: evaluation, prevention, and remedial

treatments.

Res. Pap. FPL-RP-494. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 26 p.

A limited number of free copies of this publication are available to the public from the Forest Products Laboratory, One

Gifford Pinchot Drive, Madison, WI 53705-2398. Laboratory

publications are sent to more than 1,000 libraries in the United

States.

This publication reports research involving pesticides.

It does not contain recommendations for their use,

nor does it imply that the uses discussed have been

registered. All uses of pesticides must be registered by

appropriate State and/or Federal agencies before they

can be recommended.

The use of trade or firm names in this publication is

for reader information and does not imply endorsement

by the U.S. Department of Agriculture of any product

or service.

The Forest Products Laboratory is maintained in cooperation

with the University of Wisconsin.
Contents

Page

Introduction ................. 1

Causes of deterioration ............ 1

Biological causes .............. 2

Decay fungi ............... 2

Insects ................. 2

Physical causes .............. 5

Chemical causes .............. 5

Conditions for decay ............. 5

Decay sites ............... 5

Decks .................. 6

Surface checks ............. 6

Exposed ends .............. 6

Wetted wood .............. 6

Double-plank construction ........ 6

Leakage through blacktop or

concrete overlay ............ 6

Improper positioning of plank

heartwood .............. 8

Curbs, chocks, and wales .......... 8

Seasoning and weather checks ....... 8

Infection through bolt holes ........ 8

Lap-joint construction .......... 8

Curb splits ............... 8

Improper positioning of timber

heartwood .............. 8

Stringers ................. 8

Checks and splits ............ 11

Water entry along driftpins ........ 11

Fender piles ................ 11

Decay detection ...............

Page

12

General inspection procedures ........ 12

External evidence of decay ......... 14

Methods for finding internal decay ...... 14

Sounding ................ 17

Boring ................. 17

Drilling ................ 17

Probing ................ 17

Sequential process for detecting

decay ................ 18

Decay prevention ............... 19

Preservative treatment ........... 19

Maintenance program ........... 19

Moisture control .............. 20

In-place surface preservative

treatment ............... 21

Decks ................. 22

Curbs, chocks, and wales ......... 23

Piles .................. 23

Remedial measures ............. 23

Replacement .............. 23

Reinforcement ............. 24

Fumigant treatment ........... 24

Precautions ................. 25

References .................. 26
Controlling Decay in

Waterfront Structures

Evaluation, Prevention, and

Remedial Treatments

Terry L. Highley, Supervisory Research Plant Pathologist

Forest Products Laboratory, Madison, WI

Theodore Scheffer, Research Associate

Oregon State University, Corvallis, OR

Introduction

The primary purpose of this manual is to provide information on the characteristics of decay in wood components of waterfront structures and on the means to

avoid or control decay. Most measures to protect wood

are directed against three types of destructive agents:

(1) biological (destructive utilization of wood by various micro-organisms such as decay fungi), (2) physical

(damage by breakage or deformation), and (3) chemical (such as electrolytic breakdown around iron fasteners). Biological deterioration definitely constitutes the

largest proportion of damage to structures.

Proper construction and utilization of appropriate

preservative-treated materials are the primary ingredients for a long-lasting structure. However, good construction needs to be backed up by good maintenance.

Deterioration often advances slowly and is not immediately obvious. By the time deterioration is apparent,

the trouble may be widespread. Routine inspection

can identify potential or actual problems before they

become severe. Corrective measures at early stages

may entail minor expenses, but if the deterioration is

allowed to continue, the result may be costly major

repairs or even complete demolition of the structure.

Data derived from a well-organized and executed inspection and maintenance program can be valuable for

planning new construction that will be free from the

conditions that favor deterioration. Comprehensive information about the current condition of the structures

can also prevent expensive replacements and loss of

service time during repairs. Thus, when the total cost

and service value of military and commercial marine

installations are considered, the relatively small sums

of money expended for decay-inhibiting construction,

adequate routine inspection, and proper preventive

maintenance are clearly cost-effective.

This manual is concerned almost exclusively with biological deterioration caused by decay fungi in the

above-water portions of waterfront structures. Belowwaterline decay is not a problem. The manual is

divided into three major areas: (1) deteriorating

agents, (2) decay detection and evaluation, and (3) decay prevention and remedial treatment. Many portions

of the information were derived in collaboration with

the Department of the Navy.

Causes of Deterioration

Wood does not deteriorate as a result of aging alone.

The service life of all commonly used construction

timbers depends on their protection from a variety

of deteriorating agents by means of construction and

maintenance procedures suited to the physical and

climatic features of the construction site. Deterioration of wood usually falls into one of three principal categories: (1) biological, (2) physical, and

(3) chemical.
Biological Causes

Biological damage to above-water parts of waterfront

structures is caused directly or indirectly by the activity of fungi and insects that utilize the wood for food

or nesting material.

Decay Fungi

Decay fungi are primitive plants that obtain their food

from wood (Fig. 1); they cause by far the greatest

amount of damage to the above-water components of

waterfront structures. In fact, the service life of waterfront wood is most commonly terminated as a result of decay. If wood is kept in a damp condition for

any length of time, it becomes infected with fungi that

cause decay. The rate of wood degradation depends on

the species of fungus and the kind of wood. Degradation results in loss of weight and strength of the wood.

The growing stage of the fungi is characterized by microscopic threads called hyphae that develop from germinating spores, which are analogous to seeds. The

hyphae penetrate and ramify within the wood and

cause the chemical and physical changes recognized as

decay. Under suitable conditions, fungi produce sporebearing structures called fruit bodies, from which the

fungus generally reproduces and spreads. Many decay fungi can be recognized as mushrooms or bracketshaped fruiting bodies on the surface of the infected

wood. Thousands of microscopically sized spores, analogous to seeds of higher plants, are produced in the

fruit bodies and released into the air. When the temperature is mild, spores contacting susceptible moist

wood can germinate and cause new infection.

Conditions for Growth — In common with most

organisms, decay fungi require oxygen and favorable

moisture and temperature. Oxygen is ordinarily not

a limiting factor except for wood that is under water or deep in the ground. Wood moisture contents

from about 40 to 80 percent based on ovendry weight

are most favorable for decay. These amounts of moisture occur only in green wood or as a result of wetting. Therefore, if wood is dried and then protected

against wetting, it will not decay. For a recommended

margin of safety, untreated wood should not be used

in an environment with a moisture content exceeding

20 percent. Moisture absorbed from humid air alone

(no condensation) will almost always meet this limitation. By contrast, very high moisture contents can

prevent rather than favor decay. Thus, saturated wood

that has been continuously under water can remain

comparatively sound for many years. The high moisture level prevents needed access of oxygen to typical

decay fungi.

Decay fungi differ in temperature for optimum growth.

The optimum range for most decay fungi is from about

21°C to 30°C, although some species grow slowly at

temperatures as low as 0°C and as high as 45°C. In

many areas, low temperatures from late fall to early

spring either minimize or prevent decay. The optimum

pH is in the range of 4.5 to 5.5.

Above-ground wood is less susceptible to decay than

wood in contact with the soil. This results in part

from the typically drier environment and the fact that

the wood is not in contact with decay fungi already

established in the soil. The infection of above-ground

wood depends almost solely on infection by fungal

spores, which are relatively sensitive to environmental

extremes and toxins. Natural wood extractives that

are relatively low in toxicity or lower concentrations

of wood preservatives will prevent spore infection as

opposed to infection by fungi growing in and nourished

by soil nutrients.

Classification — Typical wood decay fungi fall into

two broad classes: brown rot and white rot. The

brown-rot type of decay is much more common in

waterfront timbers, which largely are pine or Douglasfir. Brown-rot decay is usually not seen on the surface of timbers protected by preservative treatment

or in untreated members, which are protected by intermittent surface drying. Typical brown rot can be

recognized by the color and physical character of the

decayed wood. Wood with advanced decay caused by

brown-rot fungi is brittle, exhibits abnormal shrinkage

when dry, is usually brown, and typically shows distinct cross-grain checks, similar to those on the face of

heavily charred timber (Fig. 2).

White-rot fungi may occasionally be found in waterfront members made of hardwood species such as oak.

The decayed wood does not shrink abnormally; it may

be whitish or light tan and flecked with dark pencillike lines (zone lines). Typically, wood is not checked

(Fig. 3) and may have a distinctly soft and punky texture despite the absence of abnormal shrinkage.

Insects

Insect damage to the above-water components of waterfront structures is not nearly as common or destructive as decay, but it nevertheless needs to be recognized (Fig. 4). Extensive insect activity usually results

2
Figure 1—Examples of fungal growths and

associated wood decay. (A) Fruiting bodies; (B) advanced wood decay; (C) fruiting

bodies-obvious decay on wood surface;

(D) fungal growth on wood surface and advanced decay shown by checks both across

and with grain. (M 31901F)

Figure 2—Stages of brown-rot decay (Top)

Early stage-discoloration in surface and

end grain (left). (Bottom) Late stage–

cracked and collapsed wood. (M 124 928)

3
Figure 3—White-rot decay (Top) Mottling and dark zone lines (arrows) bordering the abnormally light areas in end

grain. (Bottom) Side grain in same board.

(M 124 927)

Figure 4—Types of insect damage most

likely to occur in a building. (Upper left)

Termite attack-feeding galleries (often

parallel to the grain) contain excrement

and soil. (Upper right) Powder-post beetle attack-exit holes usually filled with

wood flour and not associated with discolored wood. (Lower left) Carpenter ant

attack-nesting galleries usually cut across

grain and are free of residue. (Lower right)

Beetle at tack-feeding galleries (made

in the wood while green) free of residue

and surrounding wood darkly stained.

(M 124 884)

4
in the distortion of shape and collapse of structural

members. Various types of termites, beetles, carpenter

ants, and bees utilize wood as a food source or for

nesting purposes. Damage by wood-boring insects can

usually be recognized without difficulty. Evidence of

their presence may be entrance or departure holes,

which vary in size according to the type of insect. In

many instances, the accumulation of powdery material

in the vicinity of the hole indicates insect activity.

In general, attack by termites is more destructive than

that by other insects. Termites work inside the timbers, eating the wood and excavating large tunnels

and galleries, which sometimes hollow out the timber completely. Termites never form exit holes on the

wood surface; they carefully avoid damaging the surface. However, earthen tunnels or tubes on the wood

surface, which conceal the passage of the insects from

place to place in the wood, may indicate termite infestation. In the United States, termites are a problem

mainly in the South, but they may be troublesome in

any mild climate.

Wood rarely comes into contact with strong chemicals in waterfront structures, except in the case of accidental spilling. Most frequently, chemical damage of

wooden components is associated with metal fasteners

(Fig. 5). Wood adjacent to iron nails, screws, bolts, or

other fasteners becomes blue-black and in time softens

to varying degrees. This type of damage is commonly

referred to as “metal sickness;” the chemical deterioration is often confused with decay caused by fungi.

In advanced stages, the wood adjacent to fasteners

appears to be charred and breaks into small, cubical

pieces. A similar chemical effect has been observed

around copper or copper-alloy fasteners.

Conditions for Decay

Decay Sites

For members exposed above water or ground, weather

or seasoning checks can provide a locus for decay.

Physical Causes

Physical damage can result from overstressing, which

causes excessive deflection of structural members or

even failure to carry load. When wood members are

loaded beyond their capacity for a long time, the fibers

become permanently elongated in a process referred to

as creep. Overload may be due to greater-than-design

loading or to high moisture content of the wood, which

reduces stiffness. Although deflection may not indicate

loss of strength, the sag is usually permanent.

Wood is also overstressed by high-impact loading. Impact from berthing and mooring of ships is the chief

cause of failure of fender piling. As wood dries, shrinkage may cause checks and splits. Checks may aggravate mechanical failure of deck surfaces subjected to

considerable vehicular traffic.

Intermittent wetting by sea water occasionally causes

a type of physical damage called shredding. The salt

in the water accumulates and the resultant bulk causes

the wood fibers to separate; the surface of the affected

member consequently appears shredded.

Chemical Causes

If wood comes into contact with certain chemicals

such as strong acids or alkalis, some of the wood constituents may be decomposed.

Figure 5—Chemical damage to wood

caused by corrosion of metal fasteners.

(M 144 736)

5
Large solid-sawn members are commonly subject to

seasoning checks. When members are positioned horizontally as in decking, stringers, and curbing, any

checks on their upper surfaces and some checks on exposed side surfaces become water traps if the members

are subjected to rain or other forms of wetting. Vertically positioned members with comparable checks commonly remain dry since most checks can drain freely

when wetted.

Another point of localized wetting in waterfront members that is conducive to decay is at wood-penetrating

fasteners or hardware. Water, carrying fungus spores,

may move in alongside bolts and nails and consequently wet and infect the interior wood. The rate of

subsequent drying of the wood is comparatively slow,

and so the wood tends to remain wet between rains.

Predrilling timbers prior to pressure-preservative treatment can eliminate the danger of decay contributed by

bolt holes.

Water penetration into wood can also be significantly

influenced by the grain of the wood. End-grain (crosscut) surfaces of wood absorb water much more rapidly

than side-grain surfaces because permeability in the

longitudinal (grain) direction tends to be 50 to 100

times greater than in the transverse (across-grain)

direction. Thus, when water enters a bolt or fastener

hole, it is absorbed largely along the grain where it can

build up to critical amounts around the hole. Because

of the prominence of end grain in wood, butt joints of

untreated wood are especially vulnerable to wetting

and decay.

Decks

Deck decay is illustrated in Figures 6 through 10.

Practically all decking on waterfront structures is either Douglas-fir or Southern Pine. Conditions leading

to decay in decks are the same for both species, but

the rate of deterioration in untreated decks is considerably faster in pine than in Douglas-fir.

Surface Checks

Weather checking of the upper surface of planks is a

conspicuous feature of decks that have been in service

for a few years (Figs. 6,7). Checks can promote decay

in two ways: (1) by creating cavities in which rainwater is trapped, thereby wetting the wood sufficiently

to support attack by decay fungi, and (2) by penetrating a zone of treated wood and thereby exposing

the underlying untreated wood to infection. Moreover,

weather checks not only promote decay but may also

erode the deck surface and increase the rate of deck

wear from traffic.

The rate of decay from checks in deck planks as well

as heavier wood members can accelerate over time.

Over a period of years, incipient infection can get

established in numerous checks without causing conspicuous breakdown of wood; once the attacking fungus is established in the interior of the wood, decay

can proceed rapidly to the visible stages.

Exposed Ends

Decay can enter pressure-treated planks and timbers

through the ends where untreated wood is exposed

by cutting the members to length. If the untreated

ends are butted together, a water-trapping butt joint

is created and serious decay may result in a short time.

Untreated wood ends should be protected by flooding

with a strong solution of preservative.

Wetted Wood

Wetting decks and supports with fresh

materially shorten their service life.

water may

Double-Plank Construction

The double-plank type of construction is an invitation

to decay because the two layers of planks provide an

interzone in which water can be trapped. The deck

should contain only a single layer of planking, and the

planking should be spaced to let water pass through

the deck freely.

Leakage Through Blacktop or Concrete Overlay

Although an asphalt or concrete surface may appear to

provide a good protective cover against rain, it does

not necessarily do this. Cracks frequently develop,

particularly with blacktopped surfaces (Fig. 8), and

rainwater consequently penetrates to the underlying

planking and supporting wood members. The deck

cover retards subsequent drying, making a favorable

condition for serious decay.

Another place of decay-promoting leakage through

blacktopped and concrete decks is between the track

rails and the blacktopping or concrete in which the

rails are embedded (Fig. 9). Such leakage can be especially hazardous because the depression in the blacktop

6
Figure 6—Weather checking in upper surfaces of pier and wharf planks. A, Cross

section of Douglas-fir plank showing typical preponderance of checking on upper

weather side and rot in some checks resulting from trapping of rainwater. B, Decay,

promoted by weather checking, extending close to surface of Douglas-fir deck.

(M 130 017)

Figure 7—Cross-sectional view of planks

showing decay in one check. Stringer with

decay on upper surface also shown.

Figure 8—Blacktop cover should be properly constructed and maintained to adequately protect deck against rain wetting

and decay. A, When the track area is depressed to accommodate wheel flanges, it

tends to collect water from adjacent area.

B, Cracked blacktop.

Figure 9—A concrete deck may leak at

track positions and wet wood directly underneath. Here, decay has started along

top of stringers.

7
or concrete adjacent to the rails, necessary to accommodate wheel flanges, has a funneling effect, tending

to bring water from surrounding areas toward the rails.

Improper Positioning of Plank Heartwood

The heartwood-containing face of pine deck planks

should be positioned downward because the heartwood

may be poorly treated (Fig. 10) and because deck

decay largely occurs in the upper zone of the planking

as a result of weather checking. Heartwood from near

the pith zone should also be positioned on the lower

side of the planks because this wood is relatively weak

and easily broken; hence, it performs poorly under

traffic.

Curbs, Chocks, and Wales

Although they are not supporting members, curbs,

chocks, and wales are large and relatively expensive

timbers, fully deserving protective measures. Further

justification for their protection is the high labor cost

for replacement. Although comparatively accessible,

such timbers resist removal because they are strongly

attached to the structure and commonly carry a heavy

complement of cables and pipes.

Decay of curbs, chocks, and wales can be prevented

by deep preservative treatment, as is the case in treatment of pine sapwood. Decay in treated pine products

is usually well-controlled irrespective of construction

practices, mishandling, or long exposures. When the

wood is not treated, or when the treatment is not very

deep (as is typical in Douglas-fir), various conditions

can lead to serious decay.

Seasoning and Weather Checks

As with deck planking, checks developing in the upper

portion of curbs, chocks, and wales are the main cause

of prolonged wetting and decay in these heavier members (Fig. 11). Both seasoning and weather checks

are prevalent; because the members are large (at least

10 in. (25.4 cm) on a side), they are usually not fully

air-dry before placed in service. The large size of the

items moreover favors the development of especially

deep checks. Such checks do not dry as rapidly as the

shallower checks in planking, and thus, they present a

more severe decay hazard. In treated Douglas-fir timbers, the larger checks typically extend well below the

outer preservative-containing zone of wood (Fig. 11),

exposing the untreated wood to infection.

Infection Through Bolt Holes

Bolt holes are also a common focal point for decay.

When the holes are drilled in treated timber on the

construction site, the drilling exposes untreated wood

adjacent to the bolt (Fig. 12).

Lap-Joint Construction

The common lap-type joining of ends favors decay in

curbs and wales. The half-lap joint is most common,

and a similar connection, the oblique-scarf joint, is

occasionally seen (Fig. 12). The lap-type joint accentuates the decay hazard at the ends of timbers in two

ways: (1) by exposing a large amount of untreated interior wood in treated Douglas-fir timbers and (2) by

creating a relatively large interfacial zone where water

can be trapped. This kind of joint is also objectionable because effective on-site treating of newly exposed

wood is especially difficult. Because much of the new

surface is side grain, penetration of a preservative solution, applied by brushing or spraying, tends to be very

shallow.

Curb Splits

Splits are occasionally formed in curbs as the result of

stresses on mooring cleats (Fig. 13). Such openings

favor decay in the same way as checks that develop

from seasoning or weathering.

Improper Positioning of Timber Heartwood

As in deck planks, placement of a heartwood face can

affect the hazard of decay in pine curbs, chocks, and

wales. Heartwood is commonly present on one face; it

receives little preservative. Consequently, timbers with

heartwood should be positioned with the heartwoodcontaining face downward, where the fewest weather

checks develop.

Stringers

Failure of stringers is obviously one of the costliest

forms of damage to waterfront structures because these

timbers are a major load-bearing component. To

replace stringers, all members that they support must

be removed. Most decay in stringers begins along the

upper face, and even at early stages, decay may loosen

deck spikes. Stringer decay generally originates in

checks and splits caused by plank spikes and along

driftpins (Fig. 14).

8
Figure 11—Potential decay sites for curb,

chock, and wale timbers. A, Weather

or seasoning checks in upper surface of

Douglas-fir curb. B, Deep weather checks

in pressure-treated curb penetrate the

treated zone and subject interior wood to

decay. (M 145 019)

Figure 10—Heartwood and sapwood in

Southern Pine deck planks. A, Deck plank

with heartwood in upper surface and

wood near pith, which cause an unusually

cracked and weakened surface. B, Timbers

in cross section showing typical distribution

of preservative in heartwood and sapwood.

9
Figure 12—Half-lap-type end-joints and driftpins are prominent points of water entry

into Douglas-fir curbs and whales and thus favor decay. (Upper left) Curbing fastened

together with an oblique scarf joint. (Upper right) Joined curbs with two unnecessary features favoring decay: half-lap joint and four bolts used to attach curb to deck.

(Lower left) Deteriorated half-lap joint between curbs. (Lower right) Rot in curb from

wetting around driftpin.

Figure 13—Curb splits caused by twisting and pulling of mooring cleats. A, Typical

curb split produced by stressing of mooring cleat. B, Resultant decay.

10
Water Entry Along Driftpins

Figure 14—Typical stringer decay. A,

Extensive decay in untreated Douglas-fir

stringer. B, Loosening of deck planks on

Douglas-fir stringers caused by rotting of

wood holding stringer spikes.

Checks and Splits

Driving deck spikes directly into the wood generally

causes a split in the stringer. The splits may be quite

small and inconspicuous, but even so they furnish a

place where water can collect. Splits are likely to be

largest near the ends of the stringers. The tendency

to splitting can be aggravated in two ways: by driving the spikes in line along the grain of the stringers

and by using larger spikes than needed. Presumably,

oversized spikes are used for convenience.

1 1

Although holes are drilled for driftpins, thus precluding splitting of the stringer, water and fungi nevertheless can enter the stringer alongside the pin. The hole

enlarges somewhat with time as the wood shrinks and

swells with weather changes. This increasingly adds

to the space between pier and wood, thereby creating more and more opportunity for wetting and decay

deep in the stringer (around the driftpin).

Fender Piles

Premature failure of marine piling because of interior

decay is a major problem, which leads to costly repairs

or replacement of the wood. The U.S. Navy estimates

that over $5 million a year are spent for pile replacement (personal communication, Robert Page, formerly

Naval Facilities Engineering Command, 1973). The

damage is particularly serious in fender piles, which

are required to protect both the docking vessel and the

pier or wharf from possible impact damage.

The problem is strictly one of treated piling, since untreated piles will fail from marine-borer attack before

significant decay occurs. The principal woods used for

fender piles are Douglas-fir and Southern Pine; oak is

used in moderate quantity. Southern Pine fender piles

that are treated according to recognized standards

have little problem with decay; the treatment can penetrate deeply because most of the wood is sapwood

(Fig. 15). Decay occurs mainly with other species, especially Douglas-fir, which have relatively narrow sapwood and therefore cannot be treated deeply (Fig. 15).

Piles with narrow sapwood have an untreated heartwood center surrounded by a treated outer shell. The

untreated heartwood can constitute a considerable portion of the total pile volume. Thus, the primary avenue of infection by decay fungi is through the timber

ends where untreated wood is exposed after the piles

are cut to desired height. Decay in Douglas-fir fender

piles starts at the top and progresses downward into

the central column of untreated wood. Rate of downward progress may be about 1/2 ft (15.24 cm) per

year. Pile decay eventually extends to the high-water

level, where water soaking of the wood inhibits further

progress of the fungus. Practically all the above-water

portion of the pile can become decayed on the inside

without apparent decay on the exterior shell of treated

wood. The resultant lack of interior strength undoubtedly is responsible for much pile breakage. Yet, this

indirect but seriously damaging effect of decay seems

to be largely unrecognized.
Figure 15—Effectively and ineffectively treated piling. A, Effectively treated

Southern Pine piling. Little untreated wood is exposed by weathering checks, notching,

or boring. B, Heavily checked Douglas-fir pile; checking developed in pile 5 years after

installation. C, Typical interior rot in pressure-treated Douglas-fir pile not treated at

cutoff.

Although those who maintain fender piles recognize

that untreated wood exposed in cutting or boring on

the construction site should be at least brush treated,

they frequently do not know the limitations of this

form of treatment and the need for a pile cover to supplement the preservative treatment. A cover alone

is not likely to be effective (Figs. 16,17). Moreover,

even those who are aware of the need for both preservative treatment and pile covers overlook certain requirements for the effective application of these protective measures. Prompt application of an appropriate

preservative and cover to the cut surface can protect a

pile top against decay. The treating must be done before decay gets established. Often, covers are applied

without accompanying preservative treatment under

the misconception that the covers will protect against

rain and thus prevent sufficient moisture build-up for

decay. Simply excluding rainwater from fender piles

is not a dependable protection against decay. Decay

fungi can get established early, and moisture already

present in the pile is usually sufficient to support decay

indefinitely.

Another practice that leads to fungal infection is

notching of the pile to receive the ends of chocks or

to accommodate planks used in constructing doublemembered caps (Fig. 18). As noted with timbers, this

cutting exposes untreated wood. Sometimes the fender

piles are notched to receive the ends of the chocks

more snugly than if they were simply butted against

the pile. This practice has no real merit and therefore should be avoided, at least with Douglas-fir or oak

piles, because in these species the notching generally

will expose untreated wood. Moreover, the untreated

pile wood cannot be protected in depth by superficial

supplementary treating because the surface consists of

side grain, which is penetrated only slightly by brushed

or sprayed preservative solution. However, some evidence indicates that wood in joints can be adequately

protected by shallow penetration of the preservative if the preservative is applied in high enough

concentrations.

Decay Detection

General Inspection Procedures

Structures should be inspected routinely, and a record

should be kept of the extent of decay and the kind of

structural members affected by decay. Such a record is

necessary for an efficient maintenance program.

The climate index map for decay hazard shows the

effect of geographic location on the rate of decay

(Fig. 19). The most severe location in the United

States is the Southeast, where rainfall is plentiful and

the weather is warm and humid. In the Northeast and

Midwest, decay advances at a somewhat slower rate.

13
Figure 16—Covers for fender pile cutoffs.

A, Pile capped with raised metal collar;

hot bitumen was poured inside the collar.

B, Copper cover rendered ineffective by

hawser chafing and vandalism.

Figure 17—Bituminous coatings. A, Effective bituminous cover on Douglas-fir fender

pile. B, Ineffective bituminous cover.

13
Figure 18—Piles notched to provide firmer

contact between wale and pile or to provide

shoulders to support clamps. This practice

does not prevent decay.

Near the coast in the Northwest, decay hazard is moderate, but it can be severe on the coast. Most of the

Southwest is very dry, so the decay hazard is minimal.

The inspector should formulate a general plan of

procedure by collecting any drawings, specifications, and data pertinent to the service history of the

items to be protected. The age, size, and design of

individual waterfront structures dictate in part the inspection procedures and the equipment required for a

thorough inspection. Any available records of previous inspections, damage, repair, member replacement,

or structural modification should be noted with their

respective dates.

The actual equipment necessary for examining waterfront structures is relatively simple. It should include

hand tools for measuring, sounding, probing, drilling,

and boring, and an instrument for measuring wood

moisture content. A camera, ideally with flash attachment, is useful for providing a photographic record of

unusual circumstances.

External Evidence of Decay

locations or conditions most conducive to prolonged

wetting (Fig. 20). Decay usually results in abnormal

coloration of the wood. The first indication of decay

is often brown streaks or blotches; purplish streaks are

sometimes present (Figs. 2,3). As wood approaches

advanced stages of decay, it loses luster and may exhibit pronounced changes in color. Of course, judgments based on color necessitate familiarity with the

appearance of sound wood. Sound, healthy softwood

has a pleasant, fresh, resinous smell, whereas decayed

wood usually has a mushroom-like, stale odor. However, a musty, moldy smell, though indicative of damage conditions favorable to decay, does not necessarily

indicate the presence of decay.

The presence of fruiting bodies or “mushrooms” usually indicates that decay has become well established

in the members (Fig. 21). Advanced decay is also easy

to recognize from changes in the physical appearance

of the wood, such as localized depressions or sunken

areas over decay pockets, which reflect loss of wood

substance beneath, and cracking in cubical patterns,

which results from wood shrinkage. Evidence of retained moisture over a period of time, especially at the

junction of timbers, often indicates fungal attack.

Inspections for decay are most critical in those situations that favor decay. For example, visual evidence

of hazardous moisture conditions calls for special attention. Evidence of persistent water may appear as

watermarks. Rust stains on wood surfaces may also

indicate excessive wetting, particularly if the source

of the iron is a wood-penetrating fastener. Appreciable growth of moss or other vegetation on wood surfaces or in checks or cracks is evidence of potentially

hazardous wetting.

A small measuring tape should be available to measure

the extent of decay and width or length of checks and

splits. Another helpful tool is a thin ruler, or feeler

gauge, to determine depth of checks or condition of

fasteners at joint interfaces. A moderately pointed

tool such as an ice-pick or sharp-bladed screwdriver

is useful for probing suspected areas of decay.

Methods for Finding Internal Decay

Simple methods are available for inspecting waterfront

structures without sophisticated tools. These methods,

which include “sounding,” boring, drilling, probing,

and measuring moisture content, may be used singly or

in combination.

A good way to begin an inspection for decay is a

visual search for decay manifestations, emphasizing

14
Figure 19—Climate index for decay hazard. Higher numbers indicate greater decay

hazard. (M 144 642)

15
Figure 20—Schematic of typical areas of decay in decking,

stringers, pile covers (caps), curbing, and piling.

16
Figure 21—Decay fungal fruiting bodies in

growing (fresh) condition.

Sounding

Sounding, by rapping on the member with a hammer,

may indicate the presence of interior deterioration.

If the hammer does not rebound or produces a dull

or hollow sound, a considerable amount of the internal wood is probably decayed. This method requires

considerable experience and can be considered truly

diagnostic only where decay is relatively severe, where

large members are decayed, and where the decay extends to areas near the surface. If sounding suggests

internal decay, the wood must usually be bored to verify the diagnosis.

Boring

Boring with an increment borer is the most widely

used technique for detecting internal decay. The advantage of this method is that the removed increment

core provides an actual specimen in which the damage

can be seen. This method should be limited to areas

with conditions suitable for decay. A sharp boring bit

should be used because a dull one tends to crush or

break wood fibers and to change the appearance of the

sample. Inspectors should carry extra drill bits; cutting edges are easily damaged beyond practical field

maintenance when a bit strikes hidden fasteners. Bore

holes may become avenues for decay, and so the holes

should be properly treated. Following extraction of the

core, a wood preservative should be squirted into the

hole and the hole plugged with a preservative-treated

wood dowel.

Similarly, a plug cutter can be used to examine internal wood for decay. Plug cutters of 1/8 to 1 in.

(0.32 to 2.54 cm) diameter have been used. The

3/8-in. (0.96-cm) plug cutter is very popular because

it is commercially available, it creates only a small hole

in the member, and the samples obtained can be used

in a biological assay if necessary. The holes should be

filled with preservative-treated plugs. In addition, a

preservative should be squirted into the holes before

plugging. A saw is useful for cutting off plugs flush

with the surface.

Drilling

Drilling into the member with a sharp 1/4-in. (0.63-cm)

(approximate) bit can often be useful. A noticeable

drop in resistance to the penetration of the drill indicates decay. Chips of decayed wood brought out by

the drill tend to be darker and more easily crushed between the fingers than chips of sound wood.

Probing

Sometimes the outer surface of members consists of

only a thin solid shell and the wood underneath is

decayed. This condition can be detected by probing. Fungal decay causes wood to soften and lose its

strength. If decay is suspected, the area should be

probed with a pointed tool or a blade and the resistance of the wood compared with that of obviously

sound wood. Areas where water is likely to be absorbed or trapped by wood, such as end-grain or sidegrain faces adjacent to joints, should be probed. A

moderately pointed tool such as an ice-pick or sharpbladed screwdriver is useful for probing. Early decay

may be detected by jabbing the probe into the wood

and prying down. Sound wood, which is relatively

tough, usually breaks out in long splinters, whereas

decayed wood, which is brittle, breaks out abruptly

across the grain in short pieces (Fig. 22).

17
Figure 22—Probing test for early decay. (Left) Sound wood pries

out as long splinters. (Right) Decayed wood breaks abruptly

across grain without splintering. (M 124 721)

During inspection of wood, information about wood

moisture content is often helpful. A resistance-type

moisture meter is ideal for such a purpose because

it is simple to use and nondestructive. A reading of

>20 percent moisture content indicates that the wood

is susceptible to decay.

Moisture meters employ two elongated probes or pins

attached to a resistance meter. The meter is read at

selected points as the pins are driven into the wood.

Whether or not moisture conditions are conducive to

decay can be determined by taking moisture readings

at various sites with decay potential. Moisture readings above 25 percent after a few days of dry weather

indicate that the wood is not safe, if untreated. Moisture meters are effective only up to a depth of 3 in.

(7.62 cm), the maximum probe penetration.

For accurate readings, the meter should be frequently

calibrated and the batteries should be checked to assure that the electrode coating is intact. When using

the moisture meter in extreme cold or heat, the readings should be corrected for temperature and wood

species. Thus, temperature should be recorded along

with the meter reading. The meter manufacturer

should supply the information necessary for the corrections. A moisture meter will not give correct readings in wood treated with chromated copper arsenate

or ammoniacal copper arsenate or in wood that has

been subject to wetting by sea water. The conductive elements in these materials cause erroneously high

readings.

Sequential Process for Detecting Decay

1. Observe and record condition of wood. Initially, observe and record the general condition of piles, cross

bracing, stringers, caps, curbs, wales, chocks, and decking. Probe suspicious areas for the presence of decay

near the surface of timbers. Note any unusual damage,

loose bolts, chafing about the waterline, deep checks,

cracks, scars exposing untreated wood, and untreated

cut-off tops and ends of pilings and other members.

Also examine the surfaces for holes made by pointed

tools, exit holes made by beetles, piles of sawdust left

by carpenter ants, mud tunnels made by subterranean

termites, or wings discarded by reproductive termites.

2. Sound members. Next, sound the members with a

hammer, listening for an abnormal response. Suspicious areas should be bored to determine the nature

of the defect. Sounding will detect only members with

serious internal defects and should never be the sole

method of inspection.

3. Drill members at suspicious sites. After sounding,

drill or core members at sites where decay is suspected,

emphasizing positions adjacent to the widest checks.

Samples may be collected and submitted to a laboratory for analysis, such as culturing for decay fungi or

preservative retentions. Aluminum foil, plastic bags,

and glass or clear plastic vials are useful for transporting samples for further analysis.

18
4. Drill members at other sites. If decay is visible in

the first core, drill or core the member at other sites

to determine the distribution of the decay. Measure

the depth of preservative treatment, depth of apparently solid wood, and size of the member. The residual

strength of the member can be estimated from this

information, and depending on how the structure is

being used, decisions can be reached about future replacement or remedial treatments. If decay is present,

remember that adjacent, apparently solid, untreated

wood is probably in the early stages of decay.

5. Treat openings and plug holes. Treat all openings

made during the inspection with a preservative solution or grease and plug the holes with preservativetreated dowels slightly larger in diameter than the

inspection holes.

Decay Prevention

Preservative Treatment

Wood used under conditions conducive to decay requires preservative treatment for long service life. Two

types of preservatives can be used: oil-type preservatives, such as creosote or petroleum solutions of pentachlorophenol, and waterborne preservatives, such as

copper chrome arsenate and ammoniacal copper arsenate. In the preferred commercial treatment, the wood

is impregnated with the preservative under pressure.

Under some conditions of low-to-moderate decay hazard (e.g., above ground), the wood can be adequately

treated by brushing, spraying, dipping, or steeping.

However, once decay is established in a member, typical surface treating will not penetrate enough to eradicate the decay. In general, preservative treating is a

preventive measure, not remedial. However, fungicides

have been developed recently that penetrate deeply

into structural timbers and eradicate internal decay.

These treatments are applied as a liquid or solid in

drilled holes, from which they migrate several feet

(meters) as a toxic vapor.

Waterborne preservatives are desirable because they

leave the wood clean, non-oily, and paintable. For waterfront members, the principal disadvantage of waterborne salt treatment, compared to the more widely

used creosote or penta-oil treatments, is that it does

not impart water repellency to the wood. Checking

is also generally more severe in salt-treated than oiltreated timbers. On the other hand, some evidence

indicates that checks created by certain waterborne

treatments may facilitate the passage of fungitoxic

materials.

For material of the size and thickness commonly used

in waterfront construction, complete penetration of

the preservative into the members is generally impractical and in some woods, impossible. Instead, most

members are protected by impregnating the outer

wood sufficiently to create a toxic outer barrier to

fungal invasion. As long as this barrier is maintained

without breaks, fungi cannot invade the untreated

interior wood. The effectiveness of the preservative

barrier is determined by two factors: the thickness

of the treated wood shell (preservative penetration)

and the quantity of preservative in the treated wood

(preservative retention).

The wood of Douglas-fir trees consists mainly of heartwood, which is difficult to treat (Fig. 23). The trees

have a relatively thin sapwood of which only small

amounts are usually retained in heavy, solid-sawn

members. Even small surface seasoning checks or small

fastener penetrations, such as nails, may afford avenues

for fungi to penetrate the treated zone and reach the

untreated interior wood. Incising (a systematic pattern of punctures on the face-grain surfaces) is used

to improve preservative penetration and retention in

Douglas-fir heartwood, and it is usually specified in

treating standards.

By contrast, Southern Pine members, which have a

high percentage of sapwood, can usually be treated

relatively easily and effectively without incising. The

sapwood is readily treatable both in regard to penetration and retention of preservatives. However, the

heartwood of Southern Pine, as that of Douglasfir, is difficult to treat. The limited availability of

large, solid-sawn Southern Pine timbers has resulted

in the use of smaller, young-growth trees; gluedlaminated members can be substituted for large

members.

The moderate level of decay resistance characteristic

of Douglas-fir and Southern Pine heartwood will afford

some protection in above-ground exposures where infection is generally limited to spore germination and

where periods of high wood moisture content are not

commonly prolonged. However, much longer service

life can be obtained if the heartwood is treated adequately with appropriate wood preservatives.

Maintenance Program

When tied to a competent inspection program, regular

and timely maintenance is the most cost-effective

19
Figure 23—Cross section of incised

Douglas-fir curb showing limited penetration of preservative.

approach for achieving long service life from existing

structures. Unfortunately, maintenance is frequently

neglected until major problems develop, which eventually require closing or replacing of the structure. When

budgets are low, the first program reduced as a moneysaving measure is often maintenance; ironically, reduced maintenance substantially increases costs in the

long term.

Maintenance of waterfront structures is commonly defined as those activities necessary to preserve a structure and ensure the safety of users. In practice, all

maintenance is either preventive or remedial. That

is, it is intended to prevent a future problem or correct

an existing one. Maintenance of waterfront structures

may be divided into three arbitrary categories based

on the severity or potential severity of decay: preventive maintenance, early remedial maintenance, and

major maintenance.

Preventive maintenance involves keeping the structure

in a good state of repair to reduce the probability of

problems in the future. At this stage, decay or other

deterioration has not started, but the conditions or

potential for decay is present. Preventive maintenance

for decay problems in waterfront structures has been

largely neglected.

Early remedial maintenance is performed when decay

or deterioration is present but does not affect the

capacity or performance of the structure in normal

service. At this stage, more severe structural damage

is imminent unless corrective action is taken.

Some attempts at moisture control, such as the use of

roll roofing or sheet metal as water-diverting covers

or caps, have not resulted in the improvement sought,

and in some cases, these techniques have contributed

to increased wetting. For example, roll roofing used as

stringer covers under decking or as piling top covers

under caps may initially reduce wetting; however, as

the material ages and is used repeatedly, it becomes

permeable to water. In either new or old condition,

such material will inhibit the drying of any covered

wood that was initially wet or that has become wet.

Another example of faulty pile-top shielding is the use

of sheet metal inserts between bearing-pile tops and

20

Major maintenance involves immediate corrective measures to restore the structure to its original capacity

and condition. Deterioration has progressed to the

point where major structural components have experienced moderate to severe strength loss, and repair or

replacement is mandatory to maintain load capacity.

At this point, preventive and remedial treatments to

control decay are probably of little value. Therefore,

this aspect of maintenance will not be addressed.

This section discusses several maintenance practices

and methods applicable to waterfront structures. The

principal aims of maintenance applied to decay problems should be both the control of established decay

and the prevention of new infections. Because deficiencies can develop from many causes, each type of potential problem cannot be addressed individually. Rather,

the preventive and remedial methods presented can be

adapted to the specific circumstances of the structure.

Moisture Control

Moisture control can be used as an effective, simple,

and economical method for reducing decay in waterfront timbers. To a large extent, moisture control involves a common sense approach of identifying areas

with visible wetting or high moisture content, locating

the source of water, and taking corrective action. In

many cases, drainage patterns can be altered to prevent accumulation of water on decking. General cleaning of deck drains, deck, and other horizontal components can also maintain air circulation and prevent

prolonged exposure to trapped moisture. When water

enters through cracks or loose joints, covering with a

bituminous mastic or sealer can effectively close off the

location and prevent further water in-flow. Although

little can be done to shield members exposed to weathering, caps or other protective devices can reduce the

wetting of exposed end-grain.
caps. The metal is usually installed over the pile before the cap is placed in position. The drift pin depresses the sheet metal slightly as it is driven through

the cap and into the piling and also creates a lessthan-watertight hole in the metal. This results in a

funneling of capillary water in the metal-to-cap interface to the piling wood around the driftpin hole.

Nails through the metal into the pile top function in

the same way.

Similarly, metal caps on fender piles are generally ineffective; they invariably rupture because of mooring

hausers, vandals, or other causes (Fig. 16). Water

trapped under the covering is slow to evaporate and

adds to the decay hazard.

Bituminous or asphaltic mastics used as sealants or

bedding compounds appear to be most effective for

preventing wetting in cracks and joints and through

wood end-grain (Fig. 17). As tightly adhering coatings, these mastics eliminate troublesome capillary

spaces common with membranes and sheet metal covers. They may be applied appropriately as end-grain

coatings, joint fillers or seals, and check-filling compounds, but only if the wood is no more than moderately wet or if avenues other than those sealed are

available for drying. Care must be exercised in making

such repairs. In addition, the repairs must be maintained to ensure a watertight coating or the problem

may be compounded by formation of water entrapment

areas under the coatings.

Mastics have the advantage of lower material and installation costs than metal or membranes. Mechanically damaged or weathered and defective coatings

that are exposed and accessible can be repaired simply

by adding more coating material. However, such materials will probably be more appropriately applied as

preventive maintenance measures rather than solutions

to existing decay problems.

On structures provided with asphalt surfaces, breaks in

the surface may develop in service because of deck deflections, improper bonding, or poor construction practices (Fig. 8). When such breaks occur, they should

be repaired as soon as possible to prevent continued

and more serious deterioration. Cracking may result

from several causes but typically results from differential deck deflections at panel joints or at member

ends. When cracks appear, they should be thoroughly

cleaned with a stiff brush and compressed air, and

filled with emulsion slurry of liquid asphalt mixed with

sand. Where pavement is broken or missing, surrounding pavement should be removed to a point where

surfacing is sound and the pavement is tightly bonded

to the deck surface. For best results, the repaired area

should be square or rectangular with vertically cut

sides. After the area is cleaned, a tack coat should be

applied to the deck surface and the area patched with

a dense grade of asphalt compacted to the elevation of

the surrounding surface.

In-Place Surface Preservative Treatment

The purpose of in-place or supplemental treatments is

to prevent or arrest decay in existing structures. Such

treatments can provide a safe, effective, and economical method for extending the service life of waterfront

structures. In-place treatments were seldom used in

the past, partly because decay was not detected until

it had become visible or a member had weakened or

failed to some degree. Early detection of decay by frequent and thorough inspections eliminates this problem. Two types of in-place treatment are commonly

used: surface treatment and fumigants. Surface treatments are used to prevent infection of exposed wood,

and fumigants are used to treat internal decay.

Although maximum protection against decay is provided by pressure treating according to American

Wood-Preservers’ Association standards, in-place surface treatments can reduce the incidence of decay in

(1) newly installed, untreated wood, (2) untreated

wood exposed by weather checks or mechanical damage in poorly pressure-treated species such as Douglasfir, and (3) untreated wood exposed when pressuretreated wood members are cut or drilled. This type

of treatment is effective when applied before decay is

established. In-place surface treatment can be used

for maintaining structures because of its ease of application and effectiveness as a toxic barrier to new

infection. However, the shallow penetration of surface

treatments limits their effectiveness for established internal decay; in these cases, fumigants are much more

effective in arresting decay. Such treatments are not

intended to substitute for pressure treatment of new

wood.

In-place preservative treatments consist of various liquid or heavier grease-type preservative compounds.

The wood surface should be thoroughly saturated with

preservative so that all cracks and creases are treated;

however, care must be exercised not to apply excessive

amounts that spill or run off the surface. The effectiveness of surface treating depends on the thoroughness

of application, wood species, and moisture content of

the wood at the time of treatment. Wet wood absorbs

less preservative than dry wood during brush or spray

21
treatments. This factor is significant in waterfront pentachlorophenol two or more times using a small

structures because many areas that require treatment pressure sprayer (Table 1). Although pentachloropheare subject to wetting. Field tests show that surface nol was not effective on Southern Pine decks, FCAP

treatments in above-ground locations can effectively provided almost as much protection for the wood as it

prevent decay for at least 20 years. For waterfront ap- did for Douglas-fir. Unlike pentachlorophenol, which

plications, treatments should be systematically reap- diffuses little after penetration, water-soluble FCAP

plied at intervals of 5 to 10 years to ensure adequate moves into checks as they open, thereby protecting the

protection from decay. wood below the surface.

Decks

Surface treatment can substantially protect untreated Douglas-fir decks but not Southern Pine

decks. Douglas-fir lumber is largely heartwood and

has higher natural durability than Southern Pine,

which is mostly sapwood. In research tests, Douglasfir decking was kept essentially free of decay in Mississippi for as long as 19 years by flooding the upper

surface with fluor-chrome-arsenic-phenol (FCAP) or

Supplemental treatment of decking would ordinarily

not be warranted if the wood were pressure treated. In

Southern Pine, weather checks rarely expose untreated

wood; in pressure-treated Douglas-fir, weather checks

do expose untreated wood, but decay in checks is seldom a problem. The durability of Douglas-fir can be

attributed to the natural decay resistance of the heartwood and rapid drying of the shallow checks. Leaching

of preservative into the checks may also contribute to

durability.

Table 1—Decay of surface-treated Douglas-fir and Southern Pine

decks after 19 years of exposure in Mississippi

Wood and

treating solutiona

Treatment Number Units in decay class (no.)b

time of Average

(year) units 0 40 60 80 100 rating

Douglas-fir

Sodium penta, 5%

Sodium penta,

5% + WR

Penta in mineral

spirits, 5% + WR

FCAP, 4%

(Control)

Southern Pinec

Sodium penta, 5%

Sodium penta + WR

FCAP, 4%

(Control)

2-9 15 15

2,6 10 3

2-9 15 15

2,6 10 6

2-9 15 15

2,6 10 8

2-9 15 15

2,6 10 8

25 0

2-9 25 0

2-9 25 0

2-9 15 15

2,6 10 4

25 0

0

3

0

4

0

0

0

0

0

0

0

0

2

0

0

1

0

0

0

2

0

2

0

0

0

0

2

0

0

0

0

0

0

0

0

0

0

0

0

0

2

0

0 0

3 48

0 0

0 16

0 0

0 12

0 0

0 12

25 100

25 100

25 100

0 0

2 56

25 100

aPenta, pentachlorophenol; WR, water repellent; FCAP,

fluor-chrome-arsenic-phenol.

b Decay rated from 0 to 100. A rating of 80 indicates

sufficient decay to warrant deck plank replacement.

c Penta-treated and untreated Southern Pine deck planks

failed by year 7.

22
Curbs, Chocks, and Wales

Checks play an important role in the development of

decay in large pressure-treated Douglas-fir timbers

such as curbs, chocks, and wales. Decay may differ markedly in checks of Douglas-fir curbs pressure

treated with pentachlorophenol or creosote compared

to curbs treated with FCAP. In research tests, curbs

treated with pentachlorophenol or creosote were decayed at the base of deep checks after 4 and 10 years,

respectively. In contrast, curbs treated with FCAP

showed no decay after 17 years. Thus, the service life

of creosote- and pentachlorophenol-treated curbs with

deep checks may not be much longer than that of untreated curbs. Although creosote curbs without checking have been reported to be free of decay for as long

as 25 years, the lack of checking in these instances has

not been explained.

The absence of decay in FCAP-treated Douglas-fir

curbs with deep checks suggests a unique ability of

FCAP to protect untreated, interior wood exposed

by deep checks when the wood is not in contact with

soil. One or more constituent chemicals apparently

leach from treated to untreated wood in amounts sufficient to prevent infection by fungal spores. The outer

surfaces of the wood are not decayed, indicating that

sufficient preservative remains to protect these areas.

For curbs with deep checks, liberal application of

preservative with a brush can provide protection to

untreated wood at the base of checks. However, treatment will be successful only if the preservative is in the

checks before fungal infection occurs. Moreover, treatment may need to be repeated occasionally as long as

the checks deepen.

Piles

Premature failure of marine piling because of internal

decay is a major problem, leading to costly repair and

replacement of the wood. The damage is particularly

serious in fender piles, which protect both the docking vessel and the pier or wharf from possible impact

damage. In addition to preservative treatment, the

decay hazard can be minimized by separating curbs

and wales from the deck by filler blocks. The blocks

prevent the large water-trapping zone created when

timbers are in direct contact with the deck (Fig. 12).

For pile tops, most fungicidal treatments in combination with an intact cap will offer long-term protection

against decay. The fungicide and cap must be applied

immediately after the piles are cut off. If treatment is

delayed, decay may penetrate deep into the piling, and

the fungicide will not be effective.

Pile-capping materials should be chosen for ease of

application, long-term flexibility, cleanliness after

setting, and reasonable wear under docking stresses

(e.g., hawser scrapings). Pile caps are commonly made

from epoxy compounds, galvanized metal, bituminous

compounds, roofing felt, heavy plastic, and fiberglass

mesh cloth in combination with a bituminous material

(Fig. 16,17). Galvanized metal, roofing felts, and plastic sheets are not recommended for capping materials

because condensation or leaks can create ideal conditions for decay beneath the cap. Epoxy compounds

fail as moisture barriers because their inflexibility results in early cracking of the caps. Moreover, epoxy

compounds are costly and difficult to apply (must be

applied in a two-component system). Bituminous compounds have proved best as capping materials because

of their low cost and ease of application and repair.

Because pile caps on working piers are often damaged or pulled off by hawsers, the pile top should be

treated by flooding with a preservative before capping.

A waterborne preservative, such as ammonium bifluoride or FCAP, is apparently the most effective. These

chemicals remain inactive as long as the cap remains

sound, but they are activated in the presence of moisture. The preservative can also provide protection even

when the pile cap remains intact. By penetrating the

wood, the preservative can eliminate shallow decay below the surface caused by delay in covering the pile

top.

Grease-type preservatives troweled onto the pile cutoff

are also effective in preventing decay. The piling need

not be capped. However, such preservatives would not

be desirable in many situations because the slick pile

top could result in accidents from slippage. The ease

of application and cleanliness of waterborne preservatives make them preferable to oil-type preservatives.

Remedial Measures

Replacement

A member may need to be replaced when its residual

strength is found to be inadequate. Two aspects of replacement deserve consideration. If extended service is

anticipated, the replacement member should be pressure treated with an appropriate preservative and any

23
untreated wood exposed by cutting or boring thoroughly surface-treated. Because the removed member

had decayed when exposed to the existing conditions,

all members adjacent to the removed member should

be checked for possible decay. Whether decay is suspected or confirmed, the in-place members should be

copiously flooded with preservative before the new

member is installed.

For practicality, only the defective part of a member

may sometimes be removed and replaced. In such

cases, the described recommendations for treatment

of the replacement member apply. If the wetting that

caused decay cannot be prevented, an adequate length

of the defective material must be removed to ensure

that the infected wood has been removed. Fungal infection may extend several inches in the grain direction

beyond the visible limits of the decay. A rule of thumb

in removing decayed parts of members is to include the

visible decay plus an additional 2 ft (0.60 m) of adjacent wood in the grain direction. The newly exposed,

cutoff face of the old member as well as the replacement member should be treated with preservative in

place.

Reinforcement

When replacing a decayed member or part of a member is impractical (the replacement member cannot be

easily fitted into the structure), a sister member or reinforcing element may be used to establish the needed

load-carrying capacity. Where feasible, the old member or its defective part should be removed as a guard

against spread of the decay into the new, contacting

members.

As with replacement members, reinforcing members

should be pressure treated, and any wood exposed by

cutting or boring should be surface treated.

Fumigant Treatment

Despite pressure treatment with a preservative, large

timbers such as curbs, chocks, and wales can develop

internal decay through deep checks that penetrate the

treated shell; decay can also enter piles through cutoff

ends (Figs. 11,15). The problem is most serious with

shallow-treated species such as Douglas-fir. Preservatives applied by ordinary flooding from a brush or

spray only slightly penetrate the wood and so cannot

stop decay.

Fortunately, a type of preservative has been developed

that can move through and permeate wood that cannot be conventionally treated. The chemical, which

migrates as a gas and is called a fumigant, offers a

widely useful means for eliminating deep-seated decay. Fumigants can effectively supplement conventional

preservatives because they can be introduced at the

treatment plant.

Fumigants are applied in liquid or solid form in

predrilled holes; they then volatilize into a toxic gas

that moves through the wood, eliminating decay

fungi and insects. Fumigants can diffuse in the direction of the wood grain for over 8 ft (2.4 m) from

point of application in poles. Commonly used liquid fumigants are Vapam (33 percent sodium Nmethyldithiocarbiamate), Vorlex (20 percent methlisothiocyanate, 80 percent C-3 hydrocarbons), and

chloropicrin (trichloro-nitromethane). All three are

registered with the Environmental Protection Agency

for application to wood products. Solid chloropicrin

and 100 percent methylisothiocyanate (MIT) are available in capsules or glass tubes. Solid fumigants provide increased protection against decay, reduce risk

of environmental contamination, and can be used in

previously restricted applications.

Like nearly all other pesticides and preservatives,

fumigants are toxic to humans and must be handled

properly. They should be handled by only trained

personnel who fully understand necessary precautions

and should be applied in accordance with State and

Federal laws.

To be most effective, a fumigant should be applied at

locations where it will not leak away or be lost by diffusion to the atmosphere. When fumigants are applied,

the timbers should be inspected thoroughly to determine an optimal drilling pattern that avoids metal fasteners, seasoning checks, and severely rotted wood.

In vertical members such as piles, holes to receive liquid fumigant should be drilled at a steep angle (145°

to 60°) downward toward the center of the member,

avoiding crossing of seasoning checks. The holes should

be no more than 4 ft (1.22 m) apart and arranged in

a spiral pattern. With horizontal timbers, the holes

can be drilled straight down or slanted; slanting is generally preferable because it prevents a larger surface

area in the holes for escape of fumigant. As a rule,

the holes should be extended to within about 2 in.

(5.08 cm) of the bottom of the timber. If strength is

not jeopardized, holes can be drilled in a cluster or in

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pairs to accommodate the required amount of preservative. If large seasoning checks are present, the holes

should be drilled on each side of the member to provide better distribution of fumigant (Fig. 24). Here

also, treatment holes should be no more than 4 ft

(1.22 m) apart. If fumigant leaks from a hole, the hole

should be plugged; another hole should be drilled into

sound wood or away from the check, if a check is the

problem. As soon as the fumigant is injected, the hole

should be plugged with a tight-fitting treated wood

dowel, driven slowly to avoid splitting the wood. For

liquid fumigants, sufficient room must remain in the

treating hole so the plug can be driven without squirting the chemical out of the hole. The amount of fumigant needed and the size and number of treating

holes required depend on timber size. Liquid fumigants can be applied from l-pint (0.53-1) polyethylene

squeeze bottles, transferring the liquid from 5-gallon

(21.1-1) stock containers to the bottles by suitably

arranged tubing. Stock solution in a cylinder is sometimes dispersed to the wood directly from the cylinder. Licensed commercial fumigant treaters, following

these guidelines, can be helpful in seeing that the fumigants are introduced appropriately and safely. A

list of such treaters is available from the USDA Forest

Service, Forest Products Laboratory, Madison, Wisconsin, and the Forest Research Laboratory, Oregon State

University, Corvallis, Oregon.

Fumigants will eventually diffuse out of the wood,

allowing decay fungi to recolonize. In ongoing trials

on utility poles, Vorlex and chloropicrin have remained

effective for as long as 15 years; duration of protection

by Vapam has been somewhat less. In creosoted

waterfront curbing, chloropicrin remained effective

for at least 10 years whereas Vapam-treated timbers

needed retreatment in about 5 years. Shorter periods of protection can be expected if the fumigants are

injected close to fastener holes, splits, checks, or end

grain, where the chemical can be more easily lost by

diffusion to the atmosphere. When inspections detect

the presence of active fungi, protection by the fumigant has declined sufficiently to warrant retreatment.

One attraction of fumigant treating is that the wood

can be retreated at periodical intervals in the same

holes used for the initial treatment. The old plug is

drilled or pulled, the new fumigant is added, and the

hole is replugged with a new treated dowel.

Precautions

All wood preservatives and fumigants are toxic to humans. Therefore, special care is needed for in-place

treatment and the products must be used in accordance with State and Federal laws. Environmental and

health hazards are minimal when treatments are applied properly. The potential for environmental damage is higher in field locations because of variable conditions and the proximity to streams and other water

sources. In-place treatments must be applied only by

trained and licensed personnel who fully understand

how to apply the treatments and what safeguards to

employ. Those responsible for in-place treating should

observe the following precautions.

1. Avoid breathing preservative dusts or sprays, and

avoid bodily contact with preservative.

Figure 24—Deep seasoning checks can penetrate the shell of large pressure-treated

exterior timbers. A, Internal decay caused by water trapped in checks. B, Plugged

holes in timbers. Fumigant applied through holes stopped internal decay. Note that

treating holes are located on both sides of deep checks.

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2. Wear protective gloves and aprons when treating

lumber or when handling lumber wet with treating

solution.

3. Wash inside of gloves with water frequently.

4. Wash hands and other skin areas wetted by preservative with soap and water immediately.

5. Watch for special sensitivity to preservative, especially in persons using the preservative for the first

time. Those who showing skin sensitivity should

discontinue using the preservative.

6. Have a respirator or gas mask available when applying fumigants under adverse weather conditions.

In general, in-place treatment by local maintenance

crews is limited by the scope of the treatment required. For routine maintenance, the amount of treatment required is usually minor, and local crews can be

used when properly trained and licensed. For larger

projects involving many timber members or an entire

structure, the project should be contracted to licensed

specialists in the field. Some companies have provided

in-place treating services for many years and have excellent safety records. When selecting a contractor,

records of previous experience and performance history should be carefully evaluated to ensure that the

contractor is qualified for the job. Assistance in locating contractors may be obtained from treating

organizations or from chemical manufacturers.

References

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U.S. GOVERNMENT PRINTING OFFICE: 1989/643-043/00010