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What to Know About Basement Foundation Cracks

Not every crack in a foundation wall—either concrete block or poured concrete—is cause for concern or needs to be fixed.

basement crack Courtesy Flexomeric

Structural engineer Jim Graham follows these guidelines when assessing which ones need attention and which don’t.

How Wide are the Cracks?

On a poured foundation, a web of hairline cracks or widely spaced vertical cracks less than 1⁄8 inch wide generally mean the concrete shrank a bit too much as it cured. Unless they grow wider or leak water, these can usually be left alone. Cracks 1⁄8 inch wide or wider deserve a closer look.

What’s the Orientation?

Horizontal cracks indicate that the soil is exerting enough pressure on the wall to make it bulge inward. They’re often accompanied by diagonal cracks in poured foundations, or stair-step cracks in block foundations.

Diagonal or stair-step cracks without horizontal fissures may mean that the top of the foundation is bowing inward because it’s not properly connected to the house framing, or that the footings are settling unevenly. Any of these cracks could signal the need for major structural repairs; call in a structural engineer to determine their cause and prescribe a professional fix.

Is Water Getting In?

Graham recommends sealing stable but leaky cracks in poured foundations with epoxy (shown above), then injecting a polyurethane foam along the crack’s entire length. For block walls, he goes outside, excavates the existing soil, adds crushed stone to improve drainage, and slopes the grade away from the foundation for at least 10 feet. Both approaches should be handled by a pro who specializes in basement waterproofing.

Thanks to: Jim Graham, PE, Schaefer