Repairing Leaky Masonry Walls

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Technical Note (National Research Council of Canada. Division of Building Research), 1954-05-01

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Dickens, H. B.

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DIVISION OF BUILDiNG RESEARCH

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NOTE

No.

160

NOT FOR PUBLICATION FOR INTERNAL USE

PREPARED BY H.B. Dickens CHECKED BY

N.B.H.

APPROVED BY R.F.L.

PREPARED FOR General Distribution

- SUBJECT Repairing Leaky Masonry Walls

ｾ May

1954

Moisture may enter a masonry wall in a variety of ways. Before proceeding with an extensive repair program it is advisable -to check carefully around all window and door openings and at

coping and flashings to see whether moisture may be entering at these points. If there is any evidence of any cracks or openings at such locations these should be properly caulked and sealed.

Leakage occurring after these measures have been taken is likely to be due to faulty mortar joints or in some cases to a highly porous type of brick or block.

Repointing of Mortar Joints

Where the mortar joints are suspected the most ･ｦｦｾ｣ｴｩｶ･

remedy consists of repointing the face joints. This entails cutting or raking out the old mortar to a depth of

3/4

inch to linch

using grinding wheels or pneumatic chisels. All loose or disinte-grated material beyond this depth should also be removed. After

｣ｵｴｴｩｮｧｾ wash all dust and loose material out of the joints with a jet of water.

The masonry should be damp but not wet when repointing is begun. The mortar used should have a density no greater than the original mortar. In the absence of information on the density and proportions of the old mortar a suggested mix would be:

1:1:6 cement:lime:sand (by volume) for clay ｭ｡ｳｯｮｲｹｾ

1:2:8 or

9

cement:lime:sand (by volume) for concrete and send-lime products.

The new joints should be packed tightly and concave tooled with a rounded bar.

Grouting of Mortar Joints

A less expensive method of waterproofing leaky walls and one shown to be effective during tests at the U.S. National Bureau of Standards consists of scrubbing a cement grout into the mortar

· i

- 2

-be used to protect the adjacent masonry from discoloration. The grout should be brushed into the dampened mortar joint wi th a stiff fibre brush.

The grout mixture recommended is 1 part cement,

0.25

parts hydrated lime and 2 parts fine sand passing a No.

30

sieve (by volume).

Cracks in the masonry units themselves can be filled using the same mixture. The repointing or grouting of the face joints has the advantage of not altering the appearance

of the finished wall. Cement-water Paints

Where changing the appearance of the wall is not

ｯ｢ｪ･｣ｴｩｯｮ｡｢ｬ･ｾ an application of cement-water paint may be used to improve the moisture resistance of the wall. Tests carried out by the U.S. National Bureau of Standards on walls subjected to heavy wind-driven rain show that cement-water paint when properly applied can make a wall highly resistant to water penetration. It was also shown that the cement-water paint tended to increase in effectiveness as the result of weathering.

The application of cement-water paint should consist of two brushed-on coatings. Either factory-made or job-prepared paints may be used though commercial paints are considered more finely ground and are likely to give a more uniform colour where tinted paints are desired.

A job-mixed paint having excellent waterproofing

qualities may be made from either white or grey portland cement. Hydrated lime not exceeding

20

per cent by weight of portland cement may be added if desired. The opacity or hiding power of paint made from portland cement may be increased by the addition of 3 to

5

per cent by weight of either titanium dioxide or zinc sulphide.

The preparation of the surface and the technique of mixing and applying the paints are the most important factors affecting the durability and effectiveness of the coating. The walls should be clean and free of loose particles of mortar, grease, and wax. They should be lightly dampened using a hose with a fine fog nozzle. It is important that the masonry absorb little if any water from the wet paint; neither should the paint be thinned by drops of water standing on the surface. The paint

itself should have the consistency 'of rich cream though a slightly thinner consistency may be used for the first coating on walls of concrete units. The amount of water per ten pounds of dry powder may range from

3.25

to

4.75

quarts for commercial paints

Frequent stirring of the paint is essential to keep the paint powder ｾｮ suspension. The paint should be applied by scrubbing it into the masonry using scrub or fender brushes having stiff fibre bristles not over two inches long. Mortar

joints should be painted first. The first coat should be kept damp for at least

24

hours. When it has hardened sufficiently the wall should be again dampened and the ｳｾ｣ｯｮ､ coat applied. This coat should be kept damp for

48

hours. Roofing brushes may be used for painting smooth textured surfaces. Whitewash or paint brushes with soft bristles should never be used.

On rough textured walls, such as certain types of concrete block, the base coat can with advantage consist of a mixture of portland cement and sand well scrubbed into the maｾｯｮＺＺｹ : ｾｾｾＬＬｾｳ･ＺＺ･ＺｊｯＺ｡ｾｾＺｑ｝ｾＺ｝ｾｅｓＺｦｬｗＮ･ｾｾｾｩＦ･ＭｊＱＭｑＮＭＴｾｓＭ｢ｬｾ

ＱｦｦｩｾｯｩＺ｡ＺＺ｢ｳＭＱ｡ＺＺ］ﾣＴＮＺｬＺ｡Ｚ｢］ＧＱ｡ＭｬｳＭ｡ｾｗ＼Ｆ､ •

The Portland Cement Association has issued a useful

ｾｵｩ､･ to the application of cement-water paints. It is entitled, 'How to Paint Concrete Masonry Walls", and may be obtained on request from the Canada Cement Company, District Sales Offices,

50

King St. West, Toronto, Ontario.

Cement-water paint is particularly useful as a protective treatment for concrete block masonry which generally requires a protective coat because these large units, due to their detail e f

manufacture, cannot always be laid with a full head joint (a vital factor in moisture resistance).

Stucco Coatings

Stucco facings are also effective in preventing ｭｯｩｳｴｵｲｾ

penetration of walls providing they are carefully applied and the tops of the masonry walls are protected by projecting eaves or by flashing to prevent water from penetrating behind the stucco.

Proportions of a typical stucco mix shown to be effective by tests at the U.S. National Bureau of Standards were 100

of portland cement, 0.1 of hydrated lime and 3.0 of dry sand (by weight) with an average water content of

20.5

per cent by weight of dry materials.

Depending on the type and condition of the masonry wall, the stucco may be applied directly to it or over a wire mesh reinforcing that has been fastened securely over the entire surface of the wall. The wall should be thoroughly cleaned before the stucco is applied. Particular care should be exercised in applying a strong stucco coating to a wall built of weak masonry units such as soft brick or of units that show signs of deteri-oration as the forces set up in the drying of the stucco are likely to be sufficient to cause the masonry to spall. Even strong paint coatings have been known to remove part of the wall matertal when they have peeled off.

ｾ Ｍ Ｍ ｾ Ｍ Ｍ Ｍ

ｾ Ｍ ﾭ ｾ Ｍ Ｍ ﾭ

4

-If stucco is to be used as a protective coating for new ｣ｯｮｾｴｲｵ｣ｴｩｯｮ it is preferable to defer application until the masonry has had an opportunity to dry out as there will then be less risk of cracking.

Details of stucco application are well illustrated in another publi'cation of the Port1.and Cement Association

enti tIed, "Plastererst Manual", also obtainable from the Canada

Oement Coo, Districts Sales Offices,

50

King St. West, ｔｏｾｑｮｴｯＬ

Ontario.

Silicone Water Repellents

Where moisture penetration of a wall is due solely to capillary action through highly absorptive masonry units or to minute hair cracks in the wall, improvement may be effected by the use of the new silicone water repellents recently introduced on the market. These colourless materials show promise when used for this purpose but they will not seal large pores or cracks in masonry and therefore they cannot be considered as substitutes for repointing or grouting nor are they alternatives to dense coatings of stucco or cement-water paints. They appear to have the desirable property of adding relatively little vapour resistance to the wall but their durability cannot yet be predicted, and walls treated with these materials may have to be redone at

frequent intervals.

It should also be noted that cement-water paint, grout, plaster or mortar will not bond to a surface that has been treated with a silicone-type paint as these materials destroy the suction

qualities of the wall necessary for the bonding of cement or lime applications. Thus silicones should only be used after the final surface covering has been applied.