How To Replace The Mortar On Old Stone Foundation Walls

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Buying an old home and fixing it up is a great way to get a house with a lot of natural wood and character for a good price. The downside is that old homes generally need a lot of work to get them fixed up. One area that is especially challenging is the basement. Old homes typically have stone foundation walls that are crumbling. A crumbling stone foundation wall can let in a lot of water during periods of heavy rains that regularly occur during the springtime. If you intend to fix up the basement, you need to stabilize the stone wall before you apply a vapor barrier to the wall to help control the moisture coming into your basement. Here is how the average homeowner can stabilize an old stone foundation wall with mortar before other basement waterproofing work can take place.

You Will Need:

  • Mason Hammer
  • Fine Mist Spray Bottle
  • Soft-Bristled Brushes
  • Type-S Masonry Mortar
  • Five-Gallon Plastic Bucket
  • Pointed Trowel
  • Mortar Hawk
  • Pointing Tool

Remove Old Mortar

The first thing you need to do is remove the old crumbling mortar from between the stones on the wall. You do not have to break up the old mortar that is still holding firm and shows no signs of crumbling. Tap along the mortar seams between the stones with a masonry hammer to locate the bad mortar. You will know when you hit bad mortar because it will crumble to the floor when you hit it with a hammer.

You want to remove the first two to three inches of the mortar in the seam between the stones. Do not remove any more than this or you could destabilize the wall even further and make part of it collapse. Remove all the mortar dust in the seams with a soft-bristled brush.

Mix Mortar

You need to use a Type S masonry mortar on the foundation. Type S mortar is specifically designed for load bearing walls like stone foundation walls. All you have to do is add water to the mix. The mortar manufacturer will list on the bag how much water you need to use to properly mix the bag of mortar. Mix the mortar in a five-gallon pail.

Applying Mortar

Scoop the mortar out the pail with a trowel and put it on a mortar hawk. A mortar hawk is a tool with a handle attached to the underside of a square flat-surfaced metal pad. Carry the mortar to the wall and scrape it off the mortar hawk and into the open seams with a pointer tool. Make sure you pack enough mortar into the seam you scraped out to completely fill it up. Repeat this until all the seams you scraped out are filled with mortar.

You need to wait a couple of days before you apply a vapor barrier to the walls to allow the mortar to completely dry.