Joint Sealants

When joints fail, leaks and damage to buildings follow. this technical review of sealants can help ensure that your buildings stay tight and dry.

Modern commercial structures rely heavily on joint sealants to prevent water damage to buildings and their contents. While residential buildings use water-shedding techniques such as sloped roofs, lap siding, and overlapping flashings, many commercial designs don't; if a joint sealant fails, there is little or no barrier to leakage. Unfortunately, in today's building environment, there are many points in the design and construction process where bad judgment or bad behavior results in sealant failure. Read the following for tips on how best to avoid these situations.

Common Uses

Joint sealers are used to close open joints to keep water and air out (both exterior and interior); for appearance and cleanability (in interior surfaces where water resistance is not an issue); and to reduce sound transmission through cracks (usually interior and internal to composite assemblies). If none of the above considerations is applicable, joint sealers are probably not necessary. Although there are many types of joint sealers, this review covers joint sealants only—pourable or gunnable material of mastic consistency that sticks to each side of a joint.

Exterior. Most modern homogeneous rigid exterior substrates are purposely jointed, to allow movement without damage to the material. The two principal causes of movement are thermal expansion and contraction and seismic movement.

Some substrates, such as traditional shingling, can be overlapped to allow rainwater to run off while also allowing movement—these usually won't need sealing. Others incorporate the seal into the product design, such as metal panels with edge joints designed to prevent water infiltration.

Other combinations of exterior materials are simply different and, as a result, seldom form a watertight joint without the addition of a sealer.

The principal exterior substrates that are sealed are:

·exterior wall joints (masonry, concrete, plaster,stucco, EIFS, for example);

·door and window frames;

·concrete paving joints;

·metal flashings;

·roof joints; and

·seismic movement joints.

Interior. Joints indoors don't usually go through the thermal fluctuations that exteriors do, but they are also often jointed for other reasons. Gypsum board and plaster assemblies, for instance, often require control joints to prevent cracking. Interior joints are usually sealed to keep dirt out and make them look better. The principal interior substrates that are sealed are:

·gypsum board;


·floor control and expansion joints;

·kitchen and bathroom wet joints.