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Rain Resistant Masonry Construction Dampproofing Specifications
1) Water Repellent Treatment Recommendations
1. Water Repellent Treatment Recommendations List
In conditions created by prolonged heavy periods of rain, the application of coatings is recommended.
For the through-the-wall system, water repellent treatment is essential to obtain satisfactory rain resistance.
Rain screen walls, on the other hand, theoretically do not require coatings for rain resistance. However, coatings are still recommended to obtain maximum rain shedding and longevity of a clean surface appearance, without stains from pollution and efflorescence.
Coatings can be categorized into two classes: impermeable coatings, which seal off the passage of water or water vapor, and permeable coatings, which are effective in preventing the infiltration of rain, but allow the transpiration of entrapped moisture or moisture vapor to the outside air.
Before selecting a particular coating, the following items should be considered:
- the mechanics of moisture flow through the wall: any exterior barrier designed to prevent rain penetration, should not interfere with the normal movement of moisture to the exterior of the wall. More specifically this means that impermeable coatings should be on the inside of the wall (vapor barriers or air barriers), whereas the exterior face should be treated with a permeable barrier.
- the moisture content of the wall: even though the surface may appear to be dry, water may remain in the interior. The application of a coating may trap the water, which, if it migrates to the coated surface, can cause problems such as damaging the coating. Therefore, masonry walls must be allowed to dry out during several days of drying weather. Because of viscosity, suction rate and absorption variations, products have different requirements for surface dryness and hence the manufacturer's recommendations must be followed.
1.1. The success of the selected coating depends largely on a proper surface preparation.
A careful and thorough inspection of the masonry surface is necessary to determine the the required preparation. Cracks and openings can be of different origin: open cracks between mortar and unit due to loss of bond, units with cracks and voids, incompletely filled joints and possible settlement cracks. Openings wider than 0.5 mm (0.02 in.), in either the joints or units, should be repaired and filled. Wherever required, joints must be caulked properly; the caulking materials must be compatible with the coating.
The masonry surface must be clean and free of dust, dirt, oil, grease, efflorescence or any film left by strong cleaning agents.
Whereas excessive dust and dirt are easily removed, grease and oil may be washed off with solvent or strong alkaline solution such as lye. The residue left over by such operations must then be removed by thorough rinsing with water.
Most efflorescence can be removed by dry brushing or washing with a commercial masonry cleaner, followed by thorough rinsing with water. Adequate removal of all residues of cleaners is necessary before the surface can be coated. After cleaning efflorescence off a wall, the surface should be examined to see whether there will be a recurrence. Further efflorescence indicates either that too much water is still present, or that water is entering the wall at some defect. Precautions are necessary to prevent contact with asphaltic roofing materials, insulations, caulking and other products affected by the solvents. Other surfaces, such as aluminum, glass, etc. should be protected. Further instructions issued by manufacturers of the coating products, regarding surface preparation and precautions, should be strictly followed.
1.2. The standard test method for water permeance of masonry (ASTM E 514) describes a procedure for determining the resistance to leakage of masonry subjected to wind driven rain (ref. 18). The resulting ratings of the test specimens are arbitrary classifications for comparing relative performance. To obtain additional information on time performance of the coating, exposure in a Weather-Ometer to accelerated weathering can be useful. Results from these two tests should make objective comparison data between different coating systems possible.
1.3. The coating should produce a surface which is resistant to rain penetration. The test for water permeance of masonry (ASTM E 514) is a useful method for comparison of coatings.
The coating should maintain a surface resistant to rain penetration after long exposure to weathering. Since outdoor weathering results may take too long, an accelerated test such as exposure in a Weather-Ometer can be useful.
Before application of any coating, all voids and cracks in mortar joints and masonry units should be properly repaired.
The surface on which a coating is to be applied must be clean and dry. Dirt, stains, efflorescence, grease, etc. must be removed from the surface by approved methods.
All adjacent surfaces and materials should be protected during the application against staining or permanent damage and caulking materials must be compatible with the coating.
The type of coating will also depend upon the texture and porosity of the masonry unit used. The specifier should check with both the manufacturers of masonry units and coatings, for their recommendations on the type of coating to be used on specific surfaces.
Coatings have to be permeable to water vapor, to prevent accumulation of moisture within the wall (breathing effect).
Regarding the acceptability of the appearance, a coated test panel can give useful information for the approval of possible filming, glossing or darkening.
Application procedures and quantities must conform to the manufacturer's requirements, as should weather conditions on the day of application.
Application of clear coatings should be part of the masonry contract, in order to make one contractor responsible for the finished wall.
Water repellent treatment is not
recommended for interior brick walls.
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
