Masonry Magazine May 1972 Page. 25
Tuckpoint defective mortar joints. Remove all efflorescence by scrubbing with clear water and a stiff brush. A wall which has effloresced for a long time may present difficulties. The presence of moisture, the deposition of salts and the probable presence of alkalies are all factors which may contribute to the deterioration of paints.
If moss has accumulated on damp, shaded masonry, apply an ordinary weed killer. Wet the wall with clear water before applying weed killers to prevent them from being drawn into the wall. Chemical weed killers may contain solubles which can contribute to efflorescence or react unfavorably with paint, and should be removed after being used by scrubbing the wall with a stiff brush while rinsing with clear water.
Mildew seldom occurs on unpainted masonry. However, where present, treat it the same as on painted surfaces, discussed in the following paragraphs. Be sure to wet the wall before applying any cleaning solution. Clean small areas and rinse thoroughly. For further discussion on cleaning brick see Technical Notes 20 Revised, "Cleaning Clay Products Masonry".
Painted Surfaces. Previously painted surfaces normally require extensive preparation prior to repainting (refer to Table 2 for typical paint failures). Under humid conditions, mildew may have developed. Mildew may feed on a paint film or on particles trapped by the painted surface. If present, remove it completely before applying paint. Otherwise, growth will continue, damaging new paint. Mildew has been successfully removed by steam cleaning and sand blasting. The following is also effective:
3 oz trisodium phosphate (Soilax, Spic and Span, etc.), plus
1 oz detergent (Tide, All, etc.), plus
1 qt 5 per cent sodium hyperchlorite (Chlorox, Purex, etc.), plus
3 qt warm water, or enough to make 1 gal of solution.
Use this solution to remove mildew and dirt. Scrub with a medium soft brush until the surface is clean; then rinse thoroughly with fresh water. For small areas, use an ordinary household cleanser. Scrub with a medium soft brush and then rinse thoroughly. Use masonry paints containing a mildewcide to help prevent molds from recurring.
Remove all peeled, cracked, flaked or blistered paint by scraping, wire brushing or sand blasting. In some instances, old paint may be burned off, but this should be done only by skilled operators. Like efflorescence, paint blistering is caused by water within the masonry. Search for the water's source and take the necessary corrective measures to keep water out of the wall.
TABLE 2
Types of Paint Failures
| Defect | Description |
|---|---|
| Alligatoring | Wrinkling of the paint surface, caused by paint coats of different hardnesses |
| Bleeding | The working up of a stain into succeeding coats, imparting a discoloration to the newly applied coat |
| Blistering | Bubbles resulting from moisture trapped behind an impermeable paint film |
| Chalking | Powdering at or just beneath a paint surface. Slight chalking may be normal due to weathering |
| Checking | A defect in organic paints, manifested by slight breaks in the film surface |
| Erosion | Wearing away by weathering |
| Excessive Paint Buildup | Result of applying too much paint or coats which are too thick |
| Flaking | Detachment of small pieces |
| Map Cracking | Breaks in a paint surface extending entirely through the paint film, usually caused by shrinkage |
| Mildew | Fungus growth sometimes found feeding on paint or particles adhering to the surface in damp places, generally black or gray in color |
| Peeling | A partial detachment of paint |
| Scaling | An advanced form of flaking |
If alligatoring exists, remove the entire finish. There is no other means of correction.
If slight chalking has occurred, brush the surface thoroughly. However, if chalking is deep, remove by scrubbing with a stiff fiber brush and a solution of trisodium phosphate and water. Rinse the surface thoroughly afterwards. Use a penetrating primer to improve adhesion of the final coat.
Excessive paint buildup results from too many coats or excessively thick coats. Where it occurs, remove all paint and treat as a new surface.
Completely remove cement-based paints before repainting with other types. An exception to this rule is the use of cement-based paints as primers which will be covered by another paint within a relatively short time. If the wall will be repainted with another cement-based paint, wire brushing.