Q: What is the best way to prevent water from leaking out of the rebar holes in my basement walls?
—Tom Kujath, Farmington Hills, MIch.

A: Tom Silva replies:

Your problem—the worst of its kind I’ve ever seen—isn’t caused by rebar. What you’re seeing are metal rods called form ties, or snap ties, that held the forms together when the concrete was poured. After the concrete sets up, the forms are stripped off and the ends of the ties are snapped off just below the surface. This leaves a small pockmark at every tie location on both sides of the foundation wall. Each one should be filled with hydraulic cement to protect the ties still in the concrete from rusting. This is an important step, because rusting ties let water seep into the basement, leaving the stains you see on your walls.

You might be able to fix the problem by chiseling around each tie location to create a hole about 1⁄2 inch deep and a couple of ­inches in diameter. Chisel out as much of each tie as you can, then fill the hole with hydraulic cement. If the leaking doesn’t stop, you’ll have to take more drastic action by excavating around the outside of the foundation and patching that side. If that’s what you end up having to do, it would be a good time to see if your foundation needs a thicker waterproofing membrane and a footing drain.
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