How to Repair a Leaking Limestone Foundation

Mark the locations of all of the cracks in the foundation with spray paint. Inspect the foundation. When you see a crack, spray a little paint near it. Even small cracks can lead to problems down the road, so while you're fixing one, it's best to fix them all.

Widen the cracks with a chisel and scrape away any dirt or debris. Although it seems counterintuitive, widening the cracks will help create a better seal with the mortar patch. Stick the chisel into the crack. Scrape away any debris inside the crack and move the chisel back and forth along the edges to widen the gap.

Blend the mortar mix together. Mortar mix is a pre-packaged material that's used to patch foundations and is much easier for beginners to handle. Read the package instructions and add the required amount of water to the mortar mix and stir it.

Apply the mortar mix to the foundation with a trowel. Hold the trowel at a 15-degree angle and smooth the mortar over the crack. Use the edge of the trowel to put the mix into the crack, then smooth the mortar over with the flat part of the trowel. Continue until all of the cracks have been patched. If desired, paint over the patched areas to hide them.