How to Repair a Stone Foundation

A stone foundation is a traditional architectural element that lends an aura of grace and antiquity to American homes dating from the colonial period to the 19th Century. Even modern homes may have stone foundations because in addition to providing strong structural support for a home, they have a distinct, old world charm to them.

The problem with stone foundations is that large stones are essentially cobbled together with mortar. Over time, the stones can come loose and even fall out of place. The mortar can crumble as well. That leads to a host of problems including sagging, buckling floors, and water leaking into the foundation. Water leaks can cause even more structural damage and mold.

If you’ve noticed any of these problems in your home, the good news is that you can repair a stone foundation yourself, although it is rather labor intensive. Read the steps below to find out how.

Step 1 - Dig Deep

In order to repair your stone foundation, you need to tackle the problem from the both inside and the outside of your home. Start with the exterior. Use your shovel to dig a 1-foot deep trench along the perimeter of the stone foundation.

Step 2 - Assess the Damage

Your problem is most likely that stones have come loose and shifted out of place. Now that you can see down to the bottom of the foundation, inspect the situation and assess the damage.

Step 3 - Clean it Up

Remove loose stones that you find from the wall. Use your wire brush to scrub out dirt and debris so that you’ll have a clean surface on which to apply the mortar; otherwise, you’ll just be asking for problems down the road.

Step 4 - Mix the Mortar

Prepare the mortar according to the manufacturer’s directions. Dump it into a large bucket and mix it with water as specified.

Step 5 - Apply the Mortar

Use your trowel to spread a thick layer of the wet mortar in the areas where you removed the loose stones. Replace the stones and apply mortar to the areas around the stones, smoothing the surface with the trowel. Should any stones be missing, fill the gaps completely with mortar. Take this opportunity to look for any areas of crumbling mortar that you can touch up.

Step 6 - Let it Dry

Let the mortar dry for a minimum of 3 days. Then shovel dirt back into the trench around the house.

Step 7 - Repeat on the Interior

Now that the exterior of the foundation has been corrected, take a look at the interior, and repeat steps 2 through 6. Look for loose stones, clean out the gaps, apply mortar, and let the mortar dry.

Step 8 - Apply Sealant

Once the repair work has been done, wait at least one month so that the mortar can dry completely. Take your specially formulated cement sealant, which is available at your local hardware store, and spray it over the entire foundation to prevent future problems. Take extra care to apply plenty of sealant to the areas that have suffered damage.