Masonry Magazine May 1972 Page. 24
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MASONRY PAINTS
Because all paints have distinct properties and because surfaces vary considerably, even the most experienced painting contractors carefully examine a surface before making recommendations. However, the following will generally indicate the proper use of masonry paints. Scrubbing will suffice, providing treatments for mildew, efflorescence, etc. are not required.
CEMENT-BASED PAINTS
For many years, cement-based paints have been satisfactory coatings for masonry surfaces. They achieved popularity because they have relatively good adherence and tendency to make a wall less permeable to free water. Cement-based paints are permeable, permitting the wall to breathe. Their main components are portland cement, lime and pigments. Additives, binders and sands may be added.
Although cement-based paints are more difficult to apply than other types, good surface protection results when properly applied. While they are not complete waterproofers, cement-based paints help to seal and fill porous areas, excluding large amounts of free water. White and light colors tend to be the most satisfactory. It is difficult to obtain a uniform coating with darker shades. Lighter colors tend to become translucent when wet, and dark colors become darker. Color returns to normal as the wall surface dries. Cement-based paints can provide a good base for other paints applied within a relatively short time.
The following procedure for applying paint on a properly prepared surface generally applies:
1. Cure new masonry walls for approximately one month before applying cement-based paints.
2. Dampen wall surfaces thoroughly by spraying with water.
3. Cement-based paints are packaged in powdered form. Because their cementitious components begin to hydrate upon contact with water, mix immediately prior to application for optimum results.
4. Apply heavy coats with a stiff brush, allowing at least 24 hr to elapse between coats.
5. During this time, keep the wall damp by periodically spraying it with water.
6. Apply additional coats in the same manner.
7. Keep the final coat damp for several days to properly cure.
WATER-THINNED EMULSION PAINTS
General Characteristics. Water-thinned emulsion paints, commonly referred to as latex paints, are relatively easy to apply. Water-thinned emulsions may be brush, roller or spray-applied. However, brush application is preferable, especially on coarse-textured masonry. Emulsion paints dry quickly, have practically no odor and present no fire hazard. They may be applied to damp surfaces, permitting painting shortly after a rain or on walls damp with condensation.
As a group, these paints are alkali-resistant. Hence, neutralizing washes and curing periods are not usually necessary before painting. Water emulsion paints possess high water vapor permeability and are known to have performed well on brick substrates that have been properly prepared.
Emulsion paints will not adhere well to moderately chalky surfaces. If possible, repainting should be done before the previous coat chalks excessively. However, specifically formulated latex paints are available containing emulsified oils or emulsified alkyds which facilitate wetting of chalky surfaces. This property enables the paint to bond the chalk together and to the substrate.
The principal water-thinned emulsion paint types are: butadiene-styrene, vinyl, acrylic, alkyd and multicolored lacquers.
Butadiene-Styrene Paints
These relatively low-cost, rubber-based latex paints develop water resistance more slowly than vinyl or acrylic emulsions. They are most satisfactory in light tints as chalking rate may be excessive in deep colors.
Vinyl Paints
Polyvinyl acetate emulsion paints dry faster, have improved color retention and a more uniform, lower sheen than rubber-based latex paints.
Acrylic Emulsion Paints
Acrylic emulsions have excellent color retention, permit recoating in 30 min or less, and have good alkali resistance. Acrylics have high resistance to water spotting and may be scrubbed easily.
Alkyd Emulsion Paints
Alkyd emulsions are related to solvent-thinned alkyd types, but have all the general characteristics of latex paints. They do have more penetration than most water-thinned emulsions, achieving better adhesion on chalky surfaces. Compared to other emulsion paints, these are rather slow to dry, have more odor, are not as resistant to alkalies, and have poorer color retention. Under normal exposure conditions, alkyd emulsions can serve as a finished coat over a suitable primer.
Multicolored Lacquers
A specialized paint group, multicolored lacquers are applied only by spray gun. The finished film appears as a base color with separate dots or particles of contrasting colors. These paints will cover many surface defects and irregularities. However, they must be applied over a base coat of another type; for example, polyvinyl acetate or acrylic emulsion paints.