NRCA Roofing & Waterproofing Manual
(National Roofing Contractors Association)

Waterproofing is defined as the treatment of a surface or structure to prevent the passage of water under hydrostatic pressure. Water exerts a pressure of 62.4 pounds of force per foot (1000 kg per meter) of depth. Therefore, water lying against a barrier exerts a steadily increasing pressure as the depth increases. The waterproofing treatment must keep the water from penetrating into the building interior.

Waterproofing is used:

• To protect floors and walls below grade of buildings, tunnels, and similar structures from ground water.
• To protect spaces beneath roofs and plaza decks.
• To isolate wet spaces such as kitchens, showers, and mechanical equipment rooms from other areas of buildings.
• On bridge decks to protect against deterioration from de-icing salts and to help minimize the negative effects of thermal expansion of the structural elements and topping materials.
• To keep water from leaking from pools, planters, lagoons, irrigation trenches and dams, or into basements and other underground structures.

An understanding of the different loads and stresses placed upon the waterproofing material is important to the proper design of structures and facilities. Some of these forces are similar to those to which roofing membranes are exposed, but others are quite different.

The following are some of the performance attributes required of waterproofing materials:

• Perform for an extended period of time, preferably for the life of the structure. It is usually quite costly, if not impossible, to excavate around the foundation walls or to remove a reinforced concrete floor slab to repair or replace the waterproofing material. Consequently, unlike a roof membrane, a waterproofing membrane must perform completely trouble- and maintenance-free for an indefinite period of time.
• Perform successfully in a constantly wet environment. While there may be relatively dry periods depending on where the material is employed and the level of ground water, waterproofing is usually in continuous contact with ground water, or is retaining water, such as in a planter or pool.
• Resist environmental contaminants, such as acids or alkalis, and other contaminants. Soil chemistry varies from location to location, and sometimes from foot to foot of excavated depth. The material must be compatible with both the soil and the substrate to which it is applied. Some waterproofing materials are intolerant of certain soil salts, and others are affected by oils that could be spilled onto floors in mechanical equipment rooms. These contaminants are much different from those to which roof membranes are exposed.

This article was excerpted with permission from Residential & Light Commercial Construction Standards, available through RSMeans