Stone foundations - cause for concern?

William Kibbel III, The Home Inspector

stone foundation
Mortar has fallen out of this neglected stone foundation. Photo: William Kibbel

Stone foundations were standard fare in houses built before World War I. Today, they'rea source of frequent worry to buyers and owners of old homes.

There's good reason for this concern: If an older house suffers from sloping floors andcracked plaster, it's reasonable to suspect foundation failure as the likely cause. Buteven if the floors in your house are level and the walls crack-free, you shouldn't ignorethe foundation down below. Over the long term, neglect invites trouble.

A brief visual inspection will quickly disclose bulging, bowing, shifting or settlementof a stone foundation. If you find any one these conditions, you should call in theservices of an experienced mason.

However, if the stones are exposed, and appear generally to be where the originalbuilder placed them, you can probably handle the repairs and maintenance yourself.Determined do-it-yourselfers can perform much of the routine restoration and maintenancethat will make their home's foundation last for future generations.


Most stone foundations have, or had at some time, a mortar coating on their interior.The purpose of this coating was to help hold the stones in place.

This mortar coating will inevitably flake off from moisture migration, revealing thesurface of the stones. As this coating continues to erode, the soft, sandy mortar inbetween the stones begins to fall out. When this occurs, re-pointing is needed as soon aspossible to refill the voids where the old mortar fell out.

When repointing the exterior face of an old-house foundation, mortar needs tobe softer than the surrounding stones or bricks. For this reason, you should usually avoidpre-packaged mortar mixes -- which contain a heavy dose of "hard" Portlandcement -- for exterior old-house work.

Inside, it's a different story: Pre-packaged mortar mix can be used for the repointingand also the recoating. Simply follow the mixing instructions on the bag of mortar,troweling the mix between the stones and finishing with a complete coating.

To avoid perpetual repointing, you will need to finish with a complete top coating.This top coat does not have to look like a stone artisan's creation: It merely has toserve the purpose of keeping the old mortar in place.

Moisture penetration

Don't simply repoint and recoat without correcting underlying moisture problems.

Moisture not only erodes the mortar, but in excess, can also lead to other seriousconditions like pressure against the foundation and frost heaving in cold winter climates.

To avoid these conditions, you need to maintain proper drainage around the perimeter ofthe house:

  • Soil and surfaces of patios and walkways adjacent to the foundation should have a positive slope away from the structure.
  • Roof run-off should be collected in a well maintained gutter system and extensions should be provided on the downspouts.
  • The discharge from sump pumps, used in basements where water collects, should be directed well away from the house.

What about waterproofing systems?

In my opinion, "water proofing" systems, especially those on the exterior ofa building, should be used only as a last resort. Not only are they very costly, butthey can cause other foundation problems.

Many water proofing systems involve water collection and discharge. Whenused on the exterior of the building, the soil around the foundation is usually excavated. Problems can arise because this well compacted soil has been holding the old soft,sandy mortar firmly between the exterior of the foundation stones. Remove this soil, andit is often necessary to repoint on the exterior. In some cases stones may even beloosened and will have to be reset by a mason.

Interior water collection systems don't involve disturbing the outside soil, but still,their discharge can wash away fine soil and sand particles and eventually undermine thefoundation.

Of all the components of an old home that need either restoration or maintenance, thearea buried deep in the ground is often the most neglected. By taking these steps to keepthe mortar in between the stones, we can return to the projects exposed to daylight.

About the Author
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.

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