How to Waterproof a Basement with a Stone Foundation


How to Waterproof a Basement with a Stone Foundation

Most American homes built after World War I sit on foundations made of concrete block or poured concrete.  The refinement and wide availability of these materials, along with the advent of the trucks and highways to get them to building sites allowed the construction of stable foundations that could be built quickly and relatively inexpensively.

Before the era of poured concrete and concrete block, extending back into the earliest days of American history, the material of choice for residential foundations was stone, and with good reason.  Stone is strong, absorbs very little water and doesn’t degrade with time or exposure to soil.

Most importantly, perhaps, is that there was a lot of it, particularly in the eastern part of the country that had been settled first.  Farmers plowed up tons of fieldstone in preparing for planting and it littered the landscape in many areas.  Quarries in New England supplied granite; facilities in the Midwest and elsewhere dug and cut limestone and other materials.

Historically, stone foundations were built in one of three styles:

Rubble – found stones of varying sizes

Fieldstone – found stones of more uniform size

Cut or Dressed Stone – stone cut into blocks or shaped to fit during construction.

Although a few stone foundations were constructed dry, the majority were set in place with mortar, either with stones laid in mortar beds or with mortar used to fill openings after dry construction.  Although the stone itself remains in great condition, it is these joints, mortared or dry, that can admit water and create the need to waterproof the basement.

How to Waterproof a Stone Foundation

A stone foundation is most often waterproofed from the exterior but waterproofing can also be done on the inside for certain problems.

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.

At U.S. Waterproofing we’ve encountered our share of stone foundations during our 57 years in the basement waterproofing business and we know the best and safest ways to waterproof them cost-effectively.  Why not ask for our free advice when your stone foundation is leaking?

If you’d like to know more about the problems of stone foundations (and their solutions), please post your questions in the Comments box below.


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