4iL
The program of research on building materials and structm-es, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central Housing Committee, an informal organization of governmental agencies concerned with

housing construction and finance, which is cooperating in the investigations through a subcommittee of principal technical assistants.

CENTKAL HOUSING COMMITTEE

SUBCOMMITTEE ON TECHNICAL RESEARCH

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Federal Housing Administration.

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United States Housing Authority.

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Pierre Blouke,

Federal Home Loan Bank Board (Federal Loan Agency)

Carroll W. Chamberlain,

Public Buildings Administration (Federal Works Agency)

Joseph M. DallaValle,

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Agency).

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CHAIRMEN OP SECTIONS

Specifications Materials

Carroll W. Chamberlain Elsmere J. Walters

Maintenance

John H. Schaefer

Mechanical Equipment

Robert K. Thulman

Methods and Practices

NATIONAL BUREAU OF STANDARDS

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Phaon H. Bates,

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Warren E. Emley,

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Metallurgy.

The Forest Products Laboratory of the United States Department of Agriculture

is cooperating with both committees on investigations of wood constructions.

[For list of BMS publications and how to purchase, see cover page III.]
UNITED STATES DEPARTMENT OF COMMERCE • Harry L. Hopkins, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS41

Effect of Heating and Cooling

on the Permeability of Masonry Walls

by CYRUS c. FisHBURN and perry h. Petersen

ISSUED JANUARY 11, 1940

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly.

united states government printing office • WASHINGTON • I94O

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Foreword

This paper gives the results of further studies of the resistance of masonry walls to penetration by dampness v/hen exposed to wind-driven rains. With the changing seasons, the average temperature of the exterior walls of buildings varies within limits determined

by the geographical location of the building. Since the coefficients of thermal expansion

of masonry units and of mortars are imequal, the changes in temperature produce

differential volume changes which may result in the formation or enlargement of cracks

in mortar joints. The influence of such temperature changes has been studied by

measuring the water permeability of eleven masonry walls before, and again after they were subjected while in a dry condition, to extremes of temperature over a range of

f05° F, the minimum temperature being about 20° F. The effect of exposure to other weatliermg agencies, such as wetting and drying, or

freezing and thawing, and to local outdoor climatic conditions is also under study and

the results will be described in subsequent reports.

Lyman J. Bkiggs, Director.

II
Effect of Heating and Cooling on the Permeability of

Masonry Walls

by CYRUS c. FisHBURN and perry h. Petersen

CONTENTS

Page

Foreword ii

I. Introduction 1 n. The walls 1

1. Materials 2

2. Workmanship 3

III. Permeability tests 3

IV. Heating and cooling of the walls 3

Page

V. Discussion of permeability test data 4

1. All-brick walls 4

2. Walls with brick facings and hollow-unit backings 5

3. Walls with stucco facings 5 VI. Conclusions 6

ABSTRACT

Since the coefficients of thermal expansion of masonry

units and mortars are unequal, changes in temperature

may tend to cause cracks in the mortar joints of masonry

walls. Exposure to wind-driven rain may then result

ill the leakage of water through the walls. Permeability tests were made on 11 small masonry

wall specimens before and after exposing them to a number of cycles of heating and cooling. Seven of the specimens were l2-in. brick walls, two were of clay tile with stucco facings, and two were brick walls with

hollow-unit backings. The walls were dry when

subjected to extremes of temperature over a range of about 105° F. The maximum air temperature was

about 125° F and the minimum less than 20° F. For

each cycle, the walls were stored in the heating or cooling rooms until they attained room temperature. Data obtained from the tests indicated that repeated

exposures of dry walls to extremes of temperature did

not have an important effect on the permeability of

all-brick walls. The permeabilities of the walls with

facings of brick and backings of hollow units and of those faced with stucco increased slightly as the result

of exposure to cycles of heating and cooling.

I. INTRODUCTION

Exterior masonry walls of buildings are subjected to extremes of temperature produced byseasonal changes, the maxinmm annual range

in air temperature over the greater portion of

the United States being more than 100° F. As

the coefficients of thermal expansion of mortars

and masonry units are unequal, changes in temperature of a masonry wall produce dif- ferential volume changes which may residt in the formation of enlargement of cracks in the

mortar joints. Subsequent exposure of the wall

to wind-driven rain may then produce leaks,

the penetration of water tlu'ough cracks in the

masonry being aided by gravity, capillarity, or a

pressure gradient. The coefficient of thermal

expansion of masonry usually is withm the

following limits: ' Millionlhs per °F Clay brick 2.0 to 4.2 Mortar 4.5 to 6.5 Brick masonry 2.5 to 4.5 Concrete 4.0 to 6.0 This paper reports the effects of heating and

cooling on the permeability of masom-y walls. The walls were tested for permeability before

and after their exposure, while in a dry condition, to bathing in alternately hot and cold aii'.

II. THE WALLS

Eleven walls, about 40 in. long and about 50

in. high, having a comparatively high resist1 D. E. Parsons, Eng. News-Record 133, SI (1939).

[1]
ance to moisture penetration, were selected

from a group previously tested for permeability

and described in a publication - of the National

Bureau of Standards. Seven of them were 12-

in. brick walls, two were of structural clay tile with stucco facings, and two were brick walls

with backings of hollow units. Tlu-ee kinds

of brick, two kinds of stucco, three mortars,

and three kinds of hollow-unit backings were

represented.

All except walls 9, 2, and 3 contained two

copper flashings so placed as to collect any

leakage passing tlii'ough the wall or dropping

down the interior between the wythes. Water

passing completely through the wall was col- lected on the upper flashing. Water penetrating the facing wythe and dropping inside the

wall was collected on the lower flashing.

Walls 9, 2, and 3 contained no flashing, and it was not determined if moisture collecting on

the supporting channel at the back of the wall

had penetrated the facing or had leaked through

the bed joint between the bottom of the wall

and the channel. The materials and workmanship used in the walls are listed in table 1. The designations given in the last column of the table wfll be used to describe the walls

when referred to in the text.

Tablk 1.Description of ivalls "

Wall Number ' Kind of facing Kind of backing

Nominal thick- ness

Kind

of mortar

Desig- nation

77 Brick a.. - Brick a Inches

12 1 aal 74 do do 12 3 aaS Al Brick 6 Brick 6 12 1 bbl Ai

Ag

do

do

dodo

12

12

2

3 bb2 bbS H Brick c . Brick c 12 1 ccl 76 do do 12 3 ccS

Brick 6 Tile d 12 2 bd2 AS do Block m 12

9

2 bm2

Stucco (plain) ... Tile J 2 sj2

S'l Stucco (waterproofed). do 9 2 sj2

" All walls were of workmanship ,4, as described in BMS7, p. 10.

' The wall numbers correspond to the original numbers of the walls n BMS7; see table !, p. 7, thereof.

' The first two lower-csso letters denote the kind of masonry units

used, respectively, in the facings and backings. The final numeral is the kind of mortal used.

I Wall not flashed.

' Cyrus C. Fishburn, David Watstein, and Douglas E. Parsons, Water Permeability of Masonry Walls, Building Materials and Structures (1938) NBS Rep. BMS7.

1. Materials

Brick.—Brick a (table 1) was a low-absorptive side-cut shale brick having an absorption

during a 48-hr cold immersion of 0.6 percent

by weight and an average coefficient of thermal

expansion of 1.7 millionths per degree F over

the temperature range 14° to 104° F. Brick b was a side-cut shale brick having an absorption

of 9 percent and a coefficient of thermal expansion of 3.4 millionths per degree F. Brick c was a dry-press brick having an absorption of

17 percent and a coefficient of thermal expansion of 3.7 millionths per degree F. The

coefficients of thermal expansion of the bricks were determined by C. W. Ross, of the Bureau

staff. Stucco.—The stucco was mixed in the proportions, by weight, of 1 part of portland

cement to 3 parts of building sand. That

applied to wall 3 contained ammonium stearate

in amount equal to 0.2 percent by weight of cement. The amount of water used produced

a consistency satisfactory to the mason and

amounted to 18.7 percent by weight of dry

materials or 8.5 gal per sack of cement. Two

coats of stucco, each % to K in. thick, were

applied to each wall. Twenty-four hours

elapsed between the application of the first and second coats, and the walls were cured by

wetting daily for 3 days. The coefficient of thermal expansion of the stucco was not

determined.

Hollow-unit backings.—Structural clay tile were used for the backings of one w-all with a

brick face, wall 9, and two waUs with stucco

facings, wall 2 and 3. The backing for wall 9 was a 6-cell, double-shell, end-bearing tile. The stretcher units were 8 by 12 by lOji in., having an absorption of 2.8 percent during a

24-hr cold immersion. The backings for the

walls with stucco facings were 6-cell, 8- by 12- by 12-in. tile laid on end. These tile had an

absorption of 4.1 percent.

The coefficients of thermal expansion of the

hollow-unit backings were not determined.

Stone-concrete block, 8 by 12 by 8 in., laid on end, were used for the backing of wall AS.

These block were laid when air-dry, and they

[2]
had an absorption of 8.9 percent during a 24-

lir cold-water immersion.

Mortars.—The mortars used in the walls

differed in the relative proportions of cement

and lime. Table 2 gives the physical properties of the mortars. The masons were satisfied with the worldng properties of all of the

mortars.

Table 2.Physical properties of mortars

ProiMTf.ies Mortar 1 Mortar 2 Mortar 3

Proportions of cement, lime, sand: By dry weight 1:0.11:2.6 1:0.42:5.1 X:0. 85:7.7 Bv volume " _ . 1:0. 25:3 1:1:6 1:2:9

.\verage water content, percentage by weight of dry materials.- . 19. 3 22. 6 23.7 Compressive strength in 28 days.

lb/in.2 ' 2, 850 640 250 Flow after 1 min of suction on

porous base, percent ^ _ 86 95 97

« Proportioning was by weight, assuming portland cement weighs

94 lb/ft', dry hydrated lime 40 lb/ft', and that 1 ft^ of loose damp sand

contains 80 lb of dry sand.

' Cured according to Federal Specification SS-C-181.

' Test made for a mortar having an initial flow of 110 percent. Federal

Specification SS-C- 181b.

2. Workmanship

The method of filling the joints (designated

workmanship A in BMS7) was similar for all walls. The bed joints were spread to a uniform

thickness, and both head and collar joints were

filled solidly with mortar. Mortar was applied

to the lower edges of all brick before laying,

and, when necessary, the head and collar joints were slushed full of mortar before the bed joint

for the next course was applied. For the walls

containing hollow units faced with brick, the

joints in the brickwork were filled with mortar

as described. The brick facing was laid to the elevation of a header course and then parged on the back with about % in. of mortar before

the hollow units were set. Head joints in the

backing were completely filled, and mortar for the bed joints was placed on the top surface of

all webs and face shells.

III. PERMEABILITY TESTS

The permeability test was designed to simulate the effect of a windstorm accompanied by

a heavy rain. An isometric projection of the

test chamber and a description of the test are given in section IV-2 on page 12 of BMS?.^

3 See footnote 2.

Each wall was supported on metal skids and

clamped into position so that the face formed

one side of an airtight pressure chamber in which air pressure of 10 IhjW above atmospheric pressure was maintained. Water was

applied near the top of the wall through a per- forated metal tube so that the face was covered

with a sheet of water. The amount of water

applied over an exposed length of 35 in. was

between 10 and 15 gal per hr per linear foot of

wall (about 40 gal per hr per wall). The

relative humidity in the testing room was 80

percent or more, but the temperature of the

water applied to the walls was not recorded.

It is possible, therefore, that for some tests the water temperature was lower than that of

the air in the testing room. The tests made before heating and cooling

the walls were numbered Ax, A2, etc. (table 3),

and those tests made after the exposure to heating and cooling cycles were numbered Bi,

B2, etc. The observations made during the permeability tests were as follows: Time for appearance of moisture (dampness) on back of walls. Time for appearance of visible water on back

of walls. Time for leakage to occur on lower flashings.

Maximum rate of leakage, if any.

Extent of damp area on back of walls in 1 day.

Observations were made on the walls at short intervals during working hours and one

or more times at night. Tests on each wall were continued for at least 1 day or usually

until about 25 percent of the back of the wall was damp. The results of the observations

are given in table 3.

IV. HEATING AND COOLING OF THE

WALLS

After being given at least two permeability

tests, the walls were dried to nearly constant

weight. They were then subjected to alternate

exposures in heating and cooling rooms. The hot room used for storage of the walls was

equipped with a thermostatically controlled fan

and heater unit. The mean air temperature

within the room was about 126° F. The

[3]
average air temperature at the top of the walls was 130° F and at the bottom 123° F. After

placing five or six chilled walls in the room, the

time intervals required to raise the air temperature to the maximum values at the top and

bottom of the walls were, respectively, about

15 and 36 hours.

The cold room was equipped with a vertical

bank of brine coils along one wall. The coils were enclosed in baffles to insure circulation of

air in the room and around the coils. The

air circulation was such that the difference in

air temperature between the top and the bottom of the walls rarely exceeded 4° F. Although the cooling unit was equipped with

a thermostatically controlled valve, the air temperature was largely dependent upon the

temperature of the brine in the system so that

the average mean air temperature in the cold room was between 17° and 20° F. The walls were moved from one room to the

other every third or fourth day and about 1 week was required to complete a temperature

cycle. It was estimated that at the end of a

storage period the temperature of the masonry

at the center of the wall was within 5° F of the

mean air temperature in the room. Each of

the walls was subjected to at least 30 temperature cycles. The average range in mean air temperature per wall was between 105° and

108° F. The minimum temperature range per

cycle was 95° F and the maximum 116° F.

V. DISCUSSION OF PEKMEABILITY

TEST DATA

The permeability data and performance rat- ings for the heavy rain test, of walls listed in table 4 of BMS7 * show the wide range in per- formance between walls rated "Poor" or "Fair"

to those rated "Good" or "Excellent." The

performance ratings are arbitrary, because it

is not known how much extensive damp areas, water plainly visible in the joints, or leaks

through the wall would damage plaster applied

directly to the wall. It is probable that visible water on the back of a wall or rates of leakage

greater than 1 liter per hour from the flashings

would cause damage to the interior of a build-

' See footnote 2.

ing. The data (table 4 of BMS7) show that

for walls rated "Good" or "ExceUent" the time

interval in excess of 24 hours for extensive

penetration of moisture varies considerably.

The test exposure is more severe than natural

exposures for most building walls, and their

continuation in excess of 24 hours provides

data of diminishing practical value.

1. All-Beick Walls

The seven 12-in. all-brick walls were highly

resistant to moisture penetration in tests made

both before and after exposing them to heating

and cooling. The waUs constructed of either

brick b or brick c were more permeable than

those bunt with brick a. Unpublished data

from recent tests made by the authors on brick

masonry walls indicate that the absorptivity

of brick at the time of laying has an effect on

permeability. Although the brick c were

wetted before laying, the absorptivity, or "brick suction", of brick a was much less than

that of either brick b or brick c, and the differ- ence in wall permeabilities was largely due to the condition of the brick at the time of laying.

Wall 77 (aal) showed no penetration by dampness during test periods lasting 2 weeks and was much less permeable than wall 75 (ccS). The slight leakage, 0.01 liter per hour, from wall

Al and the late appearance of visible water,

42 ± 3 hr, on the back of wall A4 are results of negligible importance.

The data indicate that the all-brick walls were

less permeable after exposure to heating and

cooling than before. Although the time intervals for the appearance of the first or second

damp areas are, in some cases, inconsistent, it is significant that the percentages of the damp to the dry areas on the backs of the walls at 24

hours, for tests made after heating and cooling, are equal to or less than the percentages noted

for tests made before exposure to heating and

cooling. A slight decrease in permeability has

been observed for repeated permeability tests, as can be seen by comparing tests Ai and A^.

It appears, therefore, that effects of heating and

cooling on the permeability of all-brick walls were insignificant or at least not large enough to

offset the comparatively slight decrease in wall

permeability resulting from repeated exposure.

[4]
Table 3.

Data from permeabiliiy tests

Wall number

77_,

UAl

Al

A2.

H..

75,.

9'..

AS.

Designation

aaS.

bblcc3-

bm2.

Number

of temperature

cycles

33

30

30

Average

range of

air temperature

106

105

105

107

107

Test number

Al 2- -42-. Bu.- Au.

A2^ Bu

Ai.

Ai.

BiAi.. Au

B,.. A, : A;.

As,

B, . A,.. Al. Bu.

At,. Ai- Bu.

B2-. A,..

Ai..

A,.

I .42- 107 Bi.

Duration of test

Days

1415

4

5

3

12

'J'inic to failure as indicated byDamp ttirough wallFirst damp area

hr

207

37

25. 5

Second damp area

66 ±5 66 ±5 66

91 ±5 91 ±5 91

39 ±6 39 ±6 39

13. 5 16 ±3 15 26 39 33

33 ±2 33 ±2 33

18 ±4 18 ±4 18

6. 3 ±0. 2 24 15 31 ±4 31 ±4 31 41 ±7 41 ±7 41

1. 3 42 ±3 21 42 55 48

28 38 ±6 33

11 ±1 11 ±1 11 13 d=0.

14 ±0.13. 5

14. 5 16. 5 15. 5

4. fi 5.4 5

7 ±1 10 ±1 8.5

15 ±6 15 ±6 15 18 ±3 18 ±3 18 2.5 3. 5 ±0. 2 3

2. 3 9 ±0.2 5.8

2.3 2. 5 2.4

2. 3 6. 5 4.4

2. 5 11 ±0.6.7

i' 5 4 41 ±4 65 ±4 ' '53 "

58 ±2 67 ±3 62

39 ±6 54 46

255

41

39 ±6

Average

Visible water through

wall

231

3932

42 ±3

Leak

from

Hashing

(lower)

^r

Area damp

in I day

23

15 ±6"

5. 5 12

15 ±6

(")

(') C)w

%

-Vla.ti- mum

rate of leakage

JJlerKlhr

0

00

0

0

0

0

0

Trace

0. 05

. 11

« No flashings.

'> No dampness at bottom of wall.

' Damp at bottom of wall from water on supporting channel, no drip.

2. Walls With Brick Facings and HollowUnit Backings

The two walls with brick facings and hollowunit backings, 9 {bd2) and A3 {hm2), were much

more permeable than 12-in. all-brick walls of the same brick and mortar. Since the absorption of the brick used in the facings was high

and the walls contained only one parged collar

joint, it is probable that considerable water

passed through the facings, and the type of

hollow backing had little effect on permeability.

Since wall 9 {hd2) was not flashed, data on leakage could not be obtained.

Both walls showed a decrease in permeability

between tests Ai and A2 and an increase in permeability for test Bi. It would appear,

therefore, that the exposure of the walls to heating and cooling had an effect on permeability large enough to be noticeable. However,

the increase in permeability of these walls was

not sufficient to change then- performance rat- ings as given in BMS7.

3. Walls With Stucco Facings

The two stucco-faced walls showed excellent

performances imder all tests. The walls were

not flashed, but the bond between the walls and

the supporting channels was intact for tests Ai

and A2. The moving of the walls on lift trucks

during exposure to heating and cooling cycles

appeared to break this bond, and both speci- mens were damp at the bottom of the inside

[5]
face during test Bi. The dampness at the end

of 1 day, indicated for test Bi, was therefore

probably caused by moisture penetrating under

the wall and not by penetration through the stucco facing. In all tests the time for penetration, or appearance of damp areas, given in

table 3 was for areas located well above the

supporting channel.

Exposure to heating and cooling noticeably

reduced the time rec^uired for the penetration of

moisture through the walls. Hov/ever, a slight

increase in permeability has been noted for repeated tests made on other stucco walls,^ and

the increases noted for walls 2 and 3 are not

considered to be of great importance. It is possible that the repeated exposures to extremes

of temperature resulted in a slight enlargement

of old cracks and the formation of a few new

ones. There was no spalling of stucco or ex- tensive crazing noted as a result of the temperature exposures.

» Unpublished data froni tests made by the authors on stucco walls stored outdoors for 3 years.

VI. CONCLUSIONS

The following conclusions pertain to the

effects of heating and cooling on dry masonry

walls. The effects of freezing and thawing and

of temperature differences between the facing

and backing and between large walls and other

structural members were not determined.

1. The exposure to heating and cooling did

not have a significant effect on the permeability

of 12-in. all-brick masonry walls.

2. Although the data are meager, exposure to heating and cooling appeared to increase slightly

the permeability of biick walls with backings of hollow units.

3. Exposure to heating and cooling appeared

to reduce the time required for moisture to penetrate walls with stucco facings. However, the performance of the stucco-faced walls,

both before and after exposure to heating and

cooling, was comparable to that of the 12-ui. all-brick walls.

Washington, September 19, 1939.

[<>]
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BMSl Research on Building Materials and Structures for Use in Low-Cost Housing IQ^

BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions., 10^ BMS3 SuitabiUty of Fiber Insulating Lath as a Plaster Base 10^ BMS4 Accelerated Aging of Fiber Building Boards 10^ BMS5 Structural Properties of Six Masonry Wall Constructions 15^ BMS6 Survey of Roofing Materials in the Southeastern States 15^ BMS7 Water Permeability of Masonry Walls 10^ BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10^ BMS9 Structural Properties of the Insulated Steel Construction Company's "Frameless-Steel"

Constructions for Walls, Partitions, Floors, and Roofs 10^ BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 10(4 BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for WaUs and Partitions lOji BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc 15{S

BMS13 Properties of Some Fiber Building Boards of Current Manufacture 10^ BMS14 Indentation and Recovery of Low-Cost Floor Coverings 10^ BMS15 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored by

Wheehng Corrugating Co 10(4 BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 10^ BMS17 Sound Insulation of Wall and Floor Constructions lOyi BMS18 Structural Properties of "Pre-Fab" Constructions for Walls, Partitions, and Floors Sponsored by the Harnischfeger Corporation 10^ BMS19 Preparation and Revision of Building Codes 15^ BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors Sponsored by

Connecticut Pre-Cast Buildings Corporation 10^ BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association lOyS BMS22 Structural Properties of "Dun-Ti-Stone" WaU Construction Sponsored by the W. E. Dunn Manufacturing Co 10{i

BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc 10^ BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute lOji BMS25 Structural Properties of Conventional Wood-Frame Constructions for WaUs, Partitions, Floors and Roofs 15ji BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 10(4 BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by the Bender Body Co lOfi BMS28 Backflow Prevention in Over-Rim Water SuppHes lOyi BMS29 Survey of Roofing Materials in the Northeastern States 10^ BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association lOfi BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions, Sponsored by the Insulite Co 15^ BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block WaU Construction Sponsored by the National Concrete Masonry Association. 10^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Construction with

"Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co 10<i BMS41 Effect of Heating and Cooling on the Permeability of Masonry WaUs 10j5