by William L. Walker, AIA

Sealants are an important part of the building envelope system. I think of them as the third line of defense against water and vapor intrusion. The first line of defense is made up of the building skin, with its coatings, veneers, and sheathings. Membranes and flashings are secondary.

As the third line of defense, sealants are generally used to reduce the sizes of openings exposed to the weather and, particularly, to fill voids between materials that move. They should never be relied on by themselves to stop water intrusion into a wall or roof cavity. (They should not be confused with caulking, which is for thermal or sound isolation between mostly interior surfaces.)

Sealants are temporary. If selected and applied properly, a good sealant can last for five to ten years without significant reduction in performance. They should be inspected annually, and removed and replaced if they are observed to be cracking, or, as a rule of thumb, separating from a surface for more than an inch per ten feet of length (8.3 millimeters per meter).

Trouble-Shooting Sealants

There are several possible explanations for sealants coming loose from a surface. Failure can usually be attributed to incorrect material selection, joint sizing, or installation.   >>>

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Sealants are only one part of the entire building skin system. Photo: William L. Walker A sealant joint has failed prematurely due to pressure washing because the bond strength did not meet up to the forces being applied in tension, and the total width (height, in this case) of the joint exceeds recommendations. Photo: William L. Walker   Click on thumbnail images to view full-size pictures.