Masonry Magazine October 1992 Page. 27
An Information series from National Concrete Masonry Association
WATER REPELLENTS FOR CONCRETE MASONRY WALLS
NCMA-TEK
TEK 10
**Keywords:** acrylic, alkali, alkyd, coating, fill coat, integral water repellent, latex, paint, pigment volume concentration, polymer, sealer, silane, silicone, siloxane, surface treatment, water penetration, water repellent
INTRODUCTION
Water repellents are used on exterior walls to provide resistance to wind-driven rain. In addition, water repellents are used to reduce the potential for efflorescence and staining from environmental pollutants, and to enhance the color or texture of a wall.
When applied in accordance with manufacturer's recommendations, water repellents effectively control water penetration. Water repellents are generally recommended for use on single wythe concrete masonry walls exposed to the weather. The choice of water repellent will depend on the surface to be protected, the exposure conditions, and on aesthetics. A wide variety of water repellents is available, offering many choices of color, surface texture, glossiness, and application procedures.
WATER RESISTANCE
Water penetration resistance of concrete masonry walls is dependent on wall design, design for differential movement, workmanship, wall maintenance, and the application of water repellents. This TEK focuses on water repellent products for above grade walls. The other factors are discussed in NCMA-TEK 3, 85, and 126.
The effectiveness of water repellents can be evaluated in several ways. In the laboratory, ASTM E514, "Test for Water Permeance of Masonry" is currently the only standard test method for water penetration. The test simulates 5-1/2" of rain per hour with a 62.5 mph wind for a duration of 8 hours. This test is often used to evaluate water penetration before and after application of a water repellent, or to judge the relative performance of several water repellent systems.
In the field, a device known as the RILEM tube, which was developed in France, has often been used to gage resistance to water absorption.
TEK 10B © 1992 National Concrete Masonry Association
Concrete Masonry
Unit
Figure 1 RILEM Tube
RILEM
Tube
Putty
The tube, shown in Figure 1, is adhered to the wall using putty, and the graduated cylinder is filled with water. The full tube applies a pressure equivalent to an 88.5 mph wind. The speed at which the water level of the column falls indicates the relative permeability of the wall. The slower the water level falls, the more water repellent the wall is. This procedure has been used successfully to determine whether or not additional water repellent measures are indicated.
TYPES OF WATER REPELLENTS
There are two general types of water repellents: surface treatment repellents and integral water repellents. Surface treatment repellents are applied to the weather-exposed side of the wall after the wall is constructed. In addition to water repellency, surface treatment repellents also improve the stain resistance of the wall, by preventing dirt and soot from penetrating the surface, causing deep stains.
When used on new construction, water repellents should be able to resist the alkalinity of the fresh mortar. As an alternative, an alkali resistant fill coat can be applied to the wall first, or the wall can be allowed to weather for about six months, until the alkalinity is reduced. In general, surface treatment repellents should allow for vapor transmission to ensure that interior humidity within the wall and structure can escape. Treatments which are impermeable to water vapor generally fail by blistering and peeling when moisture builds up behind the exterior surface.