Masonry Magazine October 1992 Page. 29
Acrylics
Acrylics form an elastic film over the surface of masonry to provide an effective barrier to water. Acrylics dry quickly and have excellent chalk resistance. Acrylics should be applied to air-dry masonry surfaces. Costs are comparable to silicone resins.
OTHER TREATMENTS
Epoxy, Rubber, and Oil-Based Paints: These paints form impervious moisture barriers on concrete masonry surfaces. This makes for an excellent water barrier, but does not allow the wall to breathe. As such, these paints are generally not considered water repellents. These treatments are better limited to interior walls, since they can blister and peel when used on exterior walls. Oil-based paints adhere well to masonry, but are not particularly resistant to alkalis, abrasion, or chemicals. Rubber and epoxy paints offer high resistance to chemicals and corrosive gases, and are usually used in industrial applications.
APPLICATION OF SURFACE TREATMENT REPELLENTS
This section contains some general guidelines for application of surface treatments. In all cases, refer to manufacturers' literature for final recommendations and procedures. Generally, surface treatments should be applied to clean, dry walls. Wall surfaces should be cleaned in accordance with manufacturers instructions to ensure good adhesion and penetration. The wall should be allowed to dry for 3 to 5 days between cleaning or rain, and application of the repellent. All cracks and large voids should be repaired prior to applying the repellent. If caulk is used in the repair, the caulk should be compatible with the surface treatment repellent and fully cured before treatment application.
Weather can have a significant effect on the application and curing of water repellents. Usually, temperatures should remain above 40°F during the two to four days after application. There should be little or no wind during spray-on applications, to avoid an uneven coating and drift of the treatment onto other materials. Adjacent landscaping should be protected during application, and, depending on the surface treatment, it may also be necessary to protect other building materials, such as aluminum or glass.
Most manufacturers recommend applying clear surface treatments using a saturating flood coat, with a 6-8" rundown below the contact point of the spray. Sometimes it is recommended that a second coat be applied when the first is still wet. Coverage rates vary from 75 to 200 ft²/gallon depending on the surface treatment repellent used and the type and condition of the masonry.
When applying a water repellent over a previously treated wall, ensure that the new treatment is compatible with the old. With some surface treatments, masonry should be uncoated for proper adhesion. In these cases, the old treatment can be allowed to weather off, or, if time does not permit this, a pressurized wash followed by high pressure water rinse can remove previous surface treatments from masonry.
The durability of a coating is a function of the type of coating, the application procedure, the rate of application, the surface preparation, and the exposure conditions. For this reason, it is difficult to predict how the various surface treatment repellents will perform under field conditions.
INTEGRAL WATER REPELLENTS
Integral water repellents are usually polymeric products. Because integral water repellents are evenly distributed throughout the wall, they do not change the finished appearance. In addition, integral water repellents are effective at reducing efflorescence, since water migration throughout the block is reduced. As stated earlier, it is essential that the admixture be incorporated into the mortar at the jobsite, as well as into the block and any other masonry wall components, such as precast lintels. The same water repellent admixture should be used in the mortar as was used in the block, to ensure compatibility and bond.
Questions often arise regarding the effect of integral water repellents on mortar bond strength, due to the decreased water absorption. Research has shown that bond strength is primarily influenced by the mechanical interlock of mortar to the small voids in the block.
When walls containing integral water repellents are grouted, the grout produces a hydrostatic pressure which forces water into the surrounding masonry unit, allowing proper curing of the grout.
Generally, the use of other admixtures in conjunction with integral water repellents is not recommended. Other admixtures, especially accelerators, have been shown to reduce the effectiveness of integral water repellents.
Some integral water repellents are soluble when immersed in water for long periods of time. Conditions which allow standing water on any part of the wall should be avoided. For this reason, mortar joints should be tooled, rather than raked. Walls incorporating integral water repellents should not be cleaned with a high-pressure water wash.
References:
(1) "Cement and Concrete Terminology", ACI 116R-90, American Concrete Institute, 1990.
(2) "Waterproofing Materials for Masonry," Clark, E. J., Campbell, P. G., and Frohnsdorff, G., National Bureau of Standards Technical Note 883. U. S. Department of Commerce, 1975.
(3) "Clear Water Repellents for Above Grade Masonry." Sealant. Waterproofing, and Restoration Institute, 1990.
(4) "Dictionary of Scientific and Technical Terms," McGraw-Hill Publishing Company, 2nd edition.
(5) "Water Repellent Treatment of Masonry," Fornoville, Luc.. Proceedings of the Fourth Canadian Masonry Symposium, University of New Brunswick, Canada, 1986.
(6) "Application Mechanisms of Silane Waterproofers," McGet- tigan, E., Concrete International, October 1990.
(7) "Measurement of Water Absorption Under Low Pressure," RILEM Test Method 11.4, Reunion Internationale des Laboratoires D'Essais et de Recherches sur les Materiaux et les Constructions.