Caring For a Stone Foundation

The remodeling experts at Blog Cabin 2012 share tips on repairing, waterproofing and maintaining the structural integrity of a stone foundation.

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Like the house above it, the foundation of Blog Cabin 2012 represents a material medley chosen during initial construction and subsequent repairs and alterations. "There are giant cubes of granite cut from a local quarry, irregular fieldstones collected on site and even some poured concrete," says construction manager Marcus Golding of Knickerbocker Group.

That poured concrete — the stuff of cement mixer trucks — was added long after the house was built. And it remains the standard foundation-building material for its ease of application and, when applied properly, its durability.

Stone foundations aren't so maintenance free. They can last for centuries, but they require some upkeep along the way. "Anytime you're buying a house with a stone foundation, or planning a construction project above one, you need to take a close look at its condition," says Marcus.

Structural Issues

The only way to confirm the structural soundness of a stone foundation — or any portion of a home — is to bring in an inspection engineer. Still, there are telltale signs of trouble that a homeowner can spot, says Marcus, including missing or shifted stones, crumbling mortar (where applicable), cracks that run through multiple stones and areas of "subsidence" (spots where the foundation is sinking).

Every 100 years or so a stone foundation must be repointed, a process that involves chiseling old mortar away from accessible stone and replacing it with fresh material. For bigger structural concerns — none of which were discovered at Blog Cabin 2012 — repairing old stonework may require jacking up the house, disassembling the problem area, shoring up the substrate underneath it and re-laying the stones, a costly, time-consuming approach. Bolting a wood or steel beam to sound portions of the old masonry or setting it on new steel posts over new concrete piers and footings dug into the floor is a safer and simpler fix.

Water Intrusion

To waterproof an older stone foundation, curtain drains may be installed. To do so, earth surrounding the foundation is removed, a spray sealer applied to the masonry and the area refilled with gravel. A perforated plastic pipe, wrapped with filter fabric to prevent clogging, is buried in that gravel and connected to underground piping that directs any water it collects to a nearby gully or an underground collection basin. Exterior curtain drains are extremely effective, but cost $5,000 to $10,000 or more for a single wall. A homeowner should also factor in re-landscaping, necessary if trees, mature shrubs, a deck or a patio has been displaced during the process.

Rather than directing water away from the basement, it may be more affordable to collect water once it has seeped inside the basement. To install a sump pump, a hole about 18 to 36 inches in diameter and 24 to 30 inches deep is cut in the basement floor. The pump inserted in the pit features an electric motor that automatically kicks on when water in the pit rises to a certain level. The pump sucks the water up into pipes that carry it outside and away from the house. This fairly simple project costs less than $1,000, though adding a battery backup pump to work during power outages brings the price closer to $1,500.

If leaks occur in several basement locations, an interior drain system may be installed outside to gather water and channel it to the pump. This is done by cutting a trench around the perimeter of the basement floor and inserting gravel and filter fabric-wrapped, perforated piping. If water is entering through the basement walls, a plastic membrane is installed over them and tucked down into the trench. Finally, the trench is covered with concrete or a metal cap. Cost of trench installation runs from $6,000 to $7,000, depending on basement size.

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