Fieldstone Foundation - Rock Crumbling

I have a problem with my fieldstone foundation. One of the large interior rocks (3’ x 2.5’) in the foundation wall is starting to crumble and the rock is weak. Half of the rock has fallen away and the remainder is not structurally sound. Unfortunately, the rock contains a large amount of metal or minerals and they appear to have oxidized over the years. The house was built in 1895 and is located in Massachusetts.

Is this a common problem with fieldstone foundations?

What solutions are available for this problem?

Picture of rock in wall.


Angled view of wall.

Close up of rock.


Note. The rest of the foundation is in really good condition. The basement doesn’t flood and has low humidity.

Dean if I saw this during an inspection I might call it out as needing repair but overall it is a very small area and not a structural concern. Repair would include removing all loose or degraded rock cutting back the face about two inches to allow for repair material, and undercutting the edges so a repair can lock into the surrounding rock. Fill the space with hand packed hydrolic cement which will expand and lock in when drying.


Thanks for this helpful information. I’m glad the rock isn’t a structural concern. Removing the degraded rock, and cutting back to allow the new cement to lock into the surround rock makes sense.

My biggest concern would be to use hydraulic cement. The foundation is made of old lime mortar. Would the hydraulic cement be too hard and over time cause more problems?

One thought would be to use lime mortar on the rocks/edges around the spaces, let dry and then pack the hydraulic cement inside?

Image of what I’m thinking

Dean, do it as Bruce suggested, but do not use hydrolic cement, use lime mortar to make the repairs

Dean… call a professional Mason in to perform proper repairs based upon an “in-person” evaluation of the situation. It is impossible to give accurate recommendations from photos on the internet!


Your thinking is correct.
You have a problem, which is the rock breaking down.
But what is the issue?

The rock can not be sealed 100% and can not be removed and replaced (easily).

Lime mortar is sacrificial material which protects the foundation material.
Sealing the rock will likely cause more problems (as we seen in the photo). The coating of the wall is not helping.

You need to try to determine the “Problem” (look around, starting at the roof or your neighbors yard). Granite does not break down like limestone does here. Find what is causing it and address it, rather than concerning yourself with the rock repair.

Though your soil is sandy and drains well and the CS is dry, moisture is likely the problem. Being dry, the CS will increase moisture movement through the wall. This leaves mineral deposits behind which increases the moisture movement. These deposits produce a significant pressure and will crack Granite.

More information needed.