Should I repoint my field stone foundation

We live in a 200+ year old farm house. Part of which sits over a basement with an old field stone foundation. There are a few granite slabs near the top, but most are football sized or smaller rocks. We have a lot of issues with moisture, a lot of issues with bugs, and a lot of issues with rodents (we have caught mice, voles, shrews, and a rat in our house. I know not all of them would tunnel down through the foundation, but I like the idea of a more solid wall. I have also seen a toad and a salamander down there. Also, we are a little worried about the moisture causing mold issues. Part of the wall near the top has been sprayed with spray foam. Some has been mortared with some sort of cement product.

My thought is to remove what I can of the foam and cement, and then fill in all the cracks (this is repointing right?) with a lime based mortar.

Do you think this would cause any structural problems?

Do you think the lime would be the best option to stand up to Maine winters with freezing temps and all that?

Do you think the alkalinity of the lime would reduce the chance for mold

Do you think that the covering of holes would help with moisture and keeping critters out?

Thanks in advance for any thoughts.

From my observed experience, you are on the correct path.
Cement based mortar caused moisture issues, lime mortar is perfect.
Unless you start pulling stones away I see no structural problems.
Mould is most likely caused by the moisture, and steps to reduce moisture may be more effective than anything.
Another matter is the lay of the ground around the house.
200 years is a long time for levels to change, and tip water towards the building.

Unfortunately I don't have the knowledge to comment on most of the features of your repointing plans, but I recently started working for a masonry restoration company and can offer some general repointing tips.

I hope they're useful.

When you're demoing out the old mortar, you want to cut it out twice as deep as the joint is wide. So say you have a 1/2" joint you want to go 1" deep.

You also want the edges where you stop demoing to be square, not feathered. This helps the mortar adhere properly. (Not really a big issue in a 100% repoint)

Ideally your mortar should be softer than the stone, so it wears away more quickly than the stone and can be replaced. You're on the right track by not using a lot of or any cement. You definitely want to avoid "specmix" and other really hard cement based mortar mixes.

Prewet the wall before applying the new mortar, as depending on the stone it may suck all the moisture out of the new mortar and prevent it from properly curing, especially a lime mortar that likely has a long cure time.


Good luck!

I have a rubblestone foundation that was/is in a similar state. Someone filled cracks with expanding foam, other sides have a skim coat of cement. It is a mess.

I have started to methodically start from inside my basement cleaning, removing foreign substances, and restoring the lime mortar where I can. It took a while to get a decent mortar mixture but I had some advise from a local stonemason who worked on similar foundations for my mix. It is interesting to consider how the foundation 'breaths' with the changing of the seasons and expands/contracts as it goes.

It isn't hard work... it is more tedious? I find it relaxing but I only have done maybe 15% so far. It is a bad weather project.

For those that are thinking of doing their own lime-based repointing. Please respect hydrated lime, it has caustic properties that can injury you both on your skin and inhaled. I utilize gloves and a dust mask when I'm mixing and am careful of my hands and arms when applying the mortar.