Exterior Waterproofing – To waterproof a stone foundation from the exterior, an excavation is dug outside the seeping wall down to the wall’s base. (Stone foundations typically do not have footings but use a wider base to spread the building’s weight.)
The exterior of the foundation wall is cleaned of soil and cracked or deteriorated mortar is removed. Once the wall has been prepped a parge coat of fresh mortar is applied to the entire wall to create a smoother surface. After the parge coat has cured, an exterior waterproofing membrane made of asphalt-modified polyurethane is applied with a trowel in a thick coat to form a permanent water barrier.
In situations with an extremely high water table, an exterior drain tile system can also be installed to carry off ground water.
Interior Waterproofing -- A stone foundation can experience seepage through cracks in the basement floor or at the point where the floor meets the wall, either leak caused by hydrostatic pressure beneath the foundation. Installing interior drain tile, a system of perforated pipe buried in washed gravel under the basement floor, will alleviate this pressure and transport the water to a sump pump for disposal.
When doing exterior waterproofing on a stone foundation, it is critical that the homeowner select a basement waterproofing contractor with experience in working on stone foundations. Excavating around a stone foundation, when not done knowledgeably and carefully, can result in structural damage to the foundation and lead to an expensive and inconvenient repair.