Leaking Shower Pan or Base
in Seattle, WA

Traditional mortar-bed shower pans common in Seattle homes built before 1980 rely on a sloped mortar layer over a lead or PVC liner. Seattle's expansive clay soils cause subtle seasonal foundation movement that stresses the rigid mortar, eventually cracking it and breaking the watertight bond between the liner and the drain assembly. Water then migrates beneath the mortar bed and saturates the subfloor.

In Seattle homes where the shower drain collar or clamping ring has corroded — accelerated by the region's soft, slightly acidic municipal water supply — the mechanical seal between the drain body and the shower liner fails. Water bypasses the drain collar entirely and seeps into the subfloor assembly with every shower, going undetected until significant damage has accumulated.

The joint where the shower floor tile meets the wall tile or surround must be filled with flexible silicone caulk, not rigid grout, because the floor and wall planes move independently. In Seattle's wet climate this joint is under near-constant moisture stress, and if it was originally grouted or the silicone has hardened and cracked, water channels directly down through the joint onto the pan liner and eventually through any gap to the subfloor.