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Drywall and Cracking at Expansion Joints

Drywall Expansion Joint
Drywall, which is made from pressed gypsum particles, is smooth and provides a professional wall surface, but it can’t withstand pressure from foundation settling or structural shifting. Expansion joints, also called control joints, are installed in predetermined areas when constructing long wall expanses or building on soil known for its instability. Expansion joints serve as the weakest points in the wall, and their purpose is to relieve pressure on drywall that otherwise would result in cracks.

Drywall expansion joints are plastic or vinyl strips that feature a V or U shape down the center of the strip. When installed in a wall, the V or U shape expands slightly, allowing the wall to shift imperceptibly without cracking the drywall. Expansion joints are visible and are not covered by drywall joint compound.

The longer a wall or the larger a ceiling, the more it requires the installation of drywall expansion joints to reduce cracking. The joints are not common in standard residential construction unless the soil is known to move. In commercial construction, however, expansion joints are common, and architects and engineers use them to control cracking during future movement of a building.

Drywall expansion joints fit in the seam between two drywall panels. The joints are made in different sizes, and a contractor must leave a gap between the drywall panels when he attaches them to the framing beneath. Depending on the anticipated movement, an expansion joint may require a gap of 1/4 inch up to 1 inch. The expansion joint features fins on each side that attach to the adjacent drywall panels with drywall nails or spray adhesive. After the joints are in place, the contractor applies joint compound only over the fins, not over the joint.

Made of vinyl or other flexible materials, an expansion joint will expand and contract, but it should not crack unless it was taped over during installation. You may brush paint over expansion joints to minimize their appearance in a wall, but do not fill them with joint compound as you would other drywall seams.