It is important to note that clear sealers are not completely waterproof; they merely slow down the rate of water absorption into a substrate, in some situations as much as 98 percent.
However, wind-driven rain and excessive amounts of water will cause eventual leakage through any clear sealer system. This requires flashings, dampproofing, sealants, and other systems to be used in conjunction with sealers, to ensure drainage of water entering through primary envelope barriers.
This situation is similar to wearing a canvas-type raincoat. During light rain, water runs off; but should the canvas become saturated, water passes directly through the coat. Clear sealers as such are defined as water repellents, in that they shed water flow but are not impervious to water saturation or a head of water pressure.
Elastomeric coatings are high-solid-content paints that produce high-millage coatings when applied to substrates. These coatings are waterproof within normal limitations of movement and proper application.
Elastomeric coatings completely cover and eliminate any natural substrate aesthetics. They can, however, add a texture of their own to an envelope system, depending on the amount of sand, if any, in the coating.
To waterproof adequately with an elastomeric coating, details must be addressed, including patching cracks or spalls in substrates, allowing for thermal movement, and installation of flashings where necessary.
Cementitious coatings are available for application to vertical masonry substrates, which also cover substrates completely. The major limitation of cementitious above-grade product use is similar to its below-grade limitation. The products do not allow for any substrate movement or they will crack and allow water infiltration. Therefore, proper attention to details is imperative when using cementitious materials. Installing sealant joints for movement and crack preparation must be completed before cementitious coating application.
With all vertical applications, there are patching materials used to ensure water tightness of the coating applied. These products range from brushable-grade sealants for small cracks, to high-strength, quick-set cementitious patching compounds for repairing spalled substrate areas.