Masonry Magazine June 1989 Page. 19
NCMA-TEK
An Information series from National Concrete Masonry Association
55
Waterproof Coatings
For Concrete Masonry
Introduction
Techniques for waterproofing concrete masonry range from treating walls above grade for resistance to rain penetration, to protecting walls below grade against leakage from water under pressure. Waterproofing may be required during or after construction of new facilities, or for repair of existing structures.
The requirement to waterproof concrete masonry may be reduced to some extent by the design of the structure and the quality of the workmanship. Concrete masonry walls should be designed with the intention of keeping them as dry as practicable, consistent with economic and engineering factors.
Flashings, roof drains, gutters, and downspouts should be provided to divert water away from concrete masonry walls. Parapet walls should be designed with sealed copings to prevent leakage. The use of overhangs may be of great value, especially where walls face the prevailing wind. The best means of assuring dry walls below grade is to utilize waterproofing techniques on the exteriors while exposed before backfilling. Subdrainage systems should be constructed for masonry walls which may be exposed to water under hydrostatic pressure. Footings should be designed and built with adequate strength to prevent walls from cracking under structural load.
The workmanship in construction of mortar joints is a key factor in waterproofing masonry walls. Properly built mortar joints help prevent cracks from forming, and contribute to the watertightness of the finished work. Concave or "V" shaped mortar joints are the most efficient shapes, from the standpoint of impeding infiltration of rain. Compressing the mortar during joint tooling not only forms it into a shape designed to shed water, but also reduces leakage by forcing it into holes, voids, and other imperfections.
Moisture Barriers
Waterproofing masonry walls involves the application of some form of barrier to the movement of water and water vapor. The barrier may take any of several forms. Selection of the type of barrier which will produce the most successful results should be based on the mechanics of moisture flow
INTERIOR
Impermeable barrier
ABOVE GRADE
BELOW GRADE
permeable barrier
MOISTURE
EXTERIOR
permeable barrier
MOISTURE
impermeable barrier
FIGURE 1. MOISTURE FLOW THROUGH MASONRY WALLS.
TEK 55 © 1973 National Concrete Masonry Association
Concrete Units