Masonry Magazine May 1972 Page. 22
Water and Moisture
Water or moisture in a masonry system will generally hamper the satisfactory performance of the painted surface. Moisture may enter masonry walls in any of several ways; through the pores of the material, through incompletely bonded or only partially filled mortar joints, copings, sills and projections, through incomplete caulked joints and improperly installed flashing or where flashing is omitted. In general, brick wall surfaces should be dry for painting. Acceptable moisture conditions for masonry walls to receive paint are listed in Table 1. The use of an electrical moisture meter may be used to measure the moisture content of a wall.
SURFACE PREPARATION
General. Proper surface preparation is as important as paint selection. Because each coat is the foundation for all future coats, success or failure depends largely upon surface preparation. Thoroughly examine all surfaces to determine the required preparation. Previously painted surfaces often require the greatest effort. Before painting, remove all loose matter. Take special care when cleaning surfaces for emulsion paints and primers. They are nonpenetrating and require cleaner surfaces than solvent-based paints. Some paints can or should be applied to damp surfaces. Others must not. Be sure to follow directions accompanying proprietary brands.
New Masonry. As a general rule, new clay masonry is seldom painted. It is difficult to justify the extra expenditure for initial and future painting. However, if for any reason painting new masonry is desired, there are a few precautions necessary for reasonable success.
Do not wash new clay masonry walls with acid cleaning solutions. Acid reactions can result in paint failures. Use alkali-resistant paints. If low-alkali portland cement is not used in the mortar, it may be necessary to neutralize the wall to reduce the possibility of alkali-caused failures. Zinc chloride or zinc sulfate solution, 2 to 3½ lb per gal of water, is often used for this purpose.
Existing Masonry. Examine older unpainted masonry for evidence of efflorescence, mildew, mold and moss. While these conditions are not common, they all indicate the presence of moisture. Examine all possible entry points for water. Where necessary, repair flashing and caulking.
TABLE 1
Dampness of Walls and Choice of Paint
| Relative Humidity in Equilibrium With Surface, Per Cent | Wall Condition | Electrical or Hygrometric Meter Indicator (not microwave meter) | Recommendation |
|---|---|---|---|
| 100 | Wet (with obvious moisture at wall surface) | Red Zone | Chances of failure high. Postpone painting if possible. If postponement is not feasible, wipe dry and use special types of paint¹ suitable under adverse conditions. |
| 100 | Wet (no obvious water at wall surface) | Usually Red Zone | Painting is best postponed. If essential, use: (1) White cement paint (2) Special types of paint¹ |
| 90-75 | Drying | Usually Amber Zone | As above. Other porous paints give reasonable chances of success. As surface becomes drier, range may be progressively increased to include: (1) Most emulsion paints (2) Special types of permeable flat oil paints |
| Less than 75 | Dry | Usually Green Zone | No restrictions |
¹Some manufacturers offer special porous, highly pigmented emulsion paints which may give somewhat better results in very adverse conditions where delay is not acceptable.