Dampproofing, according to ACI Committee 515, is the treatment of a surface or structure to resist the passage of liquid water in the absence of hydrostatic pressure. Dampproofing is considered to involve treating concrete to retard not stop the absorption of water or water vapor by concrete or to retard the transmission of water and water vapor through concrete. It has been said that a pressure greater than a 2-inch head of water can cause water to penetrate a surface that has been dampproofed with a water repellant. Dampproofing can be done by treatment of the surface, by use of a treated cement (usually called a waterproof cement) or by incorporation of a suitable admixture. This article is concerned only with the treatment of surfaces.

When it is desirable to keep water from moving through concrete and when the water in contact with the concrete is not under pressure, dampproofing is the method to use. Dampproofing materials minimize the transmission of water vapor through concrete but do not stop it entirely. It is frequently desirable not to totally halt the passage of water vapor, because if liquid water has somehow found its way into the concrete, dampproofing materials can allow it to escape slowly as water vapor.

In applying a coating, the user should carefully follow the recommendations of the manufacturer. The condition of the surface and the ambient conditions are of considerable importance. The surface must be clean and dry and the dampproofing material should not be applied under any ambient conditions that might produce moisture or frost on the concrete surface whether from rain, snow, fog, mist, or conditions of high relative humidity and falling temperatures. The dampproofing material should never be applied if the temperature of the air or the concrete surface is lower than 40 degrees F or if it likely to fall to 32 degrees F before the coating has cured.