Sealant Joints And Gaskets

Sealants and gaskets arc clastic materials that can be placed in a joint to block the passage of air and/or water while allowing for relative movement between the two sides of the joint. A gasket is a strip of synthetic rubber that is compressed into the joint. Most sealants are mastic materials that are injected into the joint and then cure to a rubberlike state. A gasket seals against a surface by being compressed tightly against it. A sealant seals by adhering tightly to the surface.

1. The width and depth of a sealant joint must never be left to chance; they should be determined in accordance with the procedure shown on pages 35 and 36. The foam plastic backer rod is a very important part of even,' sealant joint: It limits the depth of the sealant to the predetermined dimension, provides a firm surface against which to tool the sealant, and imparts to the sealant bead the narrow-waisted shape that helps minimize stresses.

2. If the sealant joint is too narrow, normal amounts of movement between the adjoining components can overstretch the sealant and tear it.

3. If the sealant bead is too deep, stresses in the bead will be excessive and tearing is likely.

4. Tooling forces the sealant material to fill the joint, assume the desired profile, and adhere to the adjoining components. [>

Installed

Sealant

Backer rod

1. Correctly Proportioned Sealant Joint

Installed

Stretched

2. Incorrect: Joint Too Narrow

Stretched

Installed

Stretched m

Incorrect: Sealant Bead Untooled

Stretched

6. Incorrect: No Bond Breaker

Compressed

Installed

Summer Average Winter

Temperature Temperature Temperature

Applied

Sealant Applied at Average Temperature

Applied Overstretched

Sealant Applied at Winter Temperature 8. Sealant Application and Temperature

Sealant Applied at Summer Temperature Overcompressed

5, 6. In a three-sided sealant joint, a bond breaker should be inserted against the back of the joint to allow for full extension of the sealant bead when the joint opens.

7. If a sealant joint is too narrow, the sealant may become overcompressed, squeezing it out of the joint and tearing it.

8. Sealant should be applied at an air temperature that is neither too hot nor too cold. If application at very hot or very cold temperatures is anticipated, the initial joint width should be adjusted to compensate for the seasonal overstressing that might otherwise occur.

7. Incorrect: Joint Too Narrow

Installed Stretched

5. Correct: Bond Breaker in Three-Sided Joint

Installed Stretched

6. Incorrect: No Bond Breaker

Compressed

Installed

Controlling Water Leakage: Sealant Joints and Gaskets

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