Masonry Magazine May 1972 Page. 21
Technical Notes on Brick&Tile on B Construction
STRUCTURAL CLAY PRODUCTS INSTITUTE 1750 OLD MEADOW ROAD, MCLEAN, VIRGINIA 22101 PHONE 703 893-4010
INTRODUCTION
PAINTING BRICK MASONRY
Although some masonry walls require protective coatings to impart color and help in resisting rain penetration, clay masonry requires no painting or surface treatment. Brick are generally selected because, among other characteristics, they have integral and durable color and, when properly constructed, are resistant to rain penetration.
Clay masonry walls may be painted to increase light reflection or for decorative purposes. Most paint authorities agree that, once painted, exterior masonry will require repainting every three to five years.
This issue of Technical Notes discusses general applications of paint to interior and exterior brick walls, and a brief discussion on specific paints suitable for brick masonry.
GENERAL
It is often erroneously assumed that brick masonry walls that are to be painted can be built with less durable materials and, in some instances, with less than extreme care in workmanship than would normally be used for unpainted brick walls. This is not the case. When a brick wall is to be painted, the selection of materials, both brick units and mortar, and the workmanship used in constructing the wall should all be of the highest quality; at least as good in quality as when the walls are to be left exposed. Every care should be taken to see that joints are properly filled with mortar to avoid the entrance of moisture into the wall, since it may become trapped behind the paint and cause problems. Every care should be taken to see that there are no efflorescing materials in the wall, either in the mortar, brick units or in the backup, since efflorescence beneath the paint film can also cause problems. See Technical Notes 23 Series.
Brick. Brick units to be used for walls that are to be painted should conform to the applicable requirements of the ASTM Specifications for Building Brick or Facing Brick, C 62 or C 216, respectively. The grade of units (which designates their durability) should not be lower than would be used if the wall were not to be painted. Grade SW is recommended. It may be acceptable to use brick units which are durable but differ in color in a wall to be painted. However, care should be taken that the units have similar absorption and suction characteristics so that the paint applied will adhere to all of the surfaces and have a uniform acceptable appearance.
Mortar. Mortar for brick masonry walls to be painted should conform to the Specifications for Mortar for Unit Masonry, ASTM C 270, Proportion Specifications. It is suggested that the mortar consist of portland cement and lime, and that the mortar type be selected on the basis of the structural requirements of the wall. See Technical Notes 8.
Paint. Paint for application to brick masonry walls should be durable, easy to apply and have good adhesive characteristics. It should be porous if applied on exterior masonry, thereby permitting the wall to breathe and preventing the trapping of free moisture behind the paint film.
CONSIDERATIONS FOR PAINTING CLAY MASONRY
In selecting a paint system for a brick masonry wall, the primary concern should be the characteristics of the surface and the exposure conditions of the wall. A primer coat may be of particular importance, especially where unusual or severe conditions exist.
Alkalinity. The chemical property of masonry which may have a significant effect on paint durability and performance is the alkalinity of the wall. Brick are normally neutral, but are set in mortars which are chemically basic. Paint products, which are based on drying oils, may be attacked by free alkali and the oils can become saponified. To prevent this occurrence, an alkaline-resistant primer is recommended.
Efflorescence. The deposit of water-soluble salts on the surface of masonry, efflorescence, is another factor that can hamper the performance of painted masonry. Efflorescence, which is present on the surface, should be removed and, once removed, the surface should be observed for reoccurrence prior to being painted. Methods of preventing and removing efflorescence are discussed in Technical Notes, 23 Series, "Efflorescence-Causes, Prevention and Control".