How to Repair a Stone Foundation Wall

Stone wall
  • 4-12 hours
  • Advanced
  • $90-150
What You'll Need
Hydraulic cement
Spare stones
Vapor barrier
What You'll Need
Hydraulic cement
Spare stones
Vapor barrier

When discussing foundation, it generally refers to the main part supporting a building. The structural condition of the foundation of a house can easily dictate the overall soundness of the entire structure. Problems originating in the foundation will inevitably travel upward, which can lead to something as simple as cracks in a wall to something as major as an entire wall collapsing.

Modern concrete foundations have helped minimize problems with foundations, but if you live in a home that 100 years old or older, you could have a stone foundation. While concrete is poured in a single batch to create a solid foundation or basement wall, you can see that this is not the case with stone. If you look at your stone foundation, you will see that it is made up of numerous numerous stones held together with mortar. Stone foundations can be a strong and long-lasting, and many older homes supported by stone foundation are in great shape. However, the joints between the stones are often a cause for concern and need repairs.

As long as you have the right tools and accessories available, you shouldn't have any problem repairing the wall yourself. Follow these steps to repair your stone foundation.

Step 1 — Expose the Stones

Before you begin repairs on your stone foundation, you must remove anything that obstructs your view of the stone. Drywall may need to be torn down, but don't worry. It can be replaced once you have finished the project.

Step 2 — Check for Damage

Stone foundations should be inspected yearly in order to maintain the structural integrity of your home. Inspect the wall for signs of damage. Check that the blocks are all intact and that none of them have cracked. Although stone is a strong natural material, there are some stresses that could cause it to crack over time. Pay special attention to the joints between the stones. Inspect the condition of the mortar to determine whether it needs to be repaired.

If you note any of the following during your inspection, you should repair immediately:

  • loose stones
  • missing chunks of mortar
  • crumbling mortar
  • cracks in the stone or mortar

Keep in mind that cracks in the stone or through the mortar usually mean that there is an underlying problem causing the cracks. In this case, you'll have to address the cause before repairing the cracks.

Step 3 — Replace Stones

Determine the type of stone that was used to build your foundation. Three common types of stone used on foundation are limestone, sandstone, and rubble stone. Out of these three types, sandstone is the softest and rubble stone being the hardest. Knowing what rock you have is crucial because the expansion and contraction rate is different from stone to stone. This is also the case with the mortar to be used for the repair. Expansion and contraction will affect the mortar, so it also has to be selected for the job at hand. If a harder mortar is used with a softer stone, during the expansion process, the stone will press on the mortar, which is harder, thus causing the stone to crack.

To replace a stone that has loosened, cracked, broken, or chipped, chisel away the mortar from around the stone until it can be removed from the wall. Clean around the exposed areas in the wall; pick a stone that will fill the void allowing space for mortar on all sides.

Mix the mortar as per instructions from the manufacturer, depending on the amount of mortar needed, mixing can be done by hand in a wheelbarrow or larger amounts you may want to use a mixer.

Using a pointed trowel, lay down a thick bed of mortar on the bottom of the opening for the stone to set on. Slide the stone through the hole and rest it on the bed of mortar. Now use the trowel to force mortar around the stone on the remaining three sides. Make sure that the mortar goes completely through and out the other side.

Clean up the mortar line with a brush to give a clean, professional look.

Step 4 — Fill Cracks

Use hydraulic cement to fill cracks in the walls. The hydraulic cement simply needs to be pushed into each of the cracks to ensure that they are filled sufficiently. If the cracks are filled, the wall will be immediately strengthened. Even tiny cracks pose tremendous risk, especially if they become wet, so it is important that this repair is done as soon as the problem is noticed.

Step 5 — Mortar Joints

If the mortar has shrunk or deteriorated, it will need to be replaced. Chip the failed mortar out about 2 to 3 inches deep. Scrape away the old mortar and replace it with a new mix. Use the appropriate mortar for your stone and, mix according to manufactures instructions. Using your trowel, push the mortar into the joint to fill the void and clean off excess with the brush.

Be sure to clean the stones before you apply the new mortar.

Step 6 — Brace Walls

If any of the walls are bowed, you will steel beams or wall anchors to stop them from moving any further. Talk to a professional if you are not sure how this will work.

Step 7 - Vapor Barriers

If your stone basement wall is suffering from dampness and mold, you can remedy the problem with a vapor barrier. A vapor barrier is a simple sheet of rubber material that is fixed to the inside of the wall. It prevents water from entering your house. Cut the vapor barrier to size and fix it to the wall with nails and use tape or caulk to fully seal the gaps. Once the vapor barrier is in place, install your drywall over it and continue as normal.