Author Topic: Repoint fieldstone foundation?  (Read 730 times)

littlebird

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Repoint fieldstone foundation?
« on: January 29, 2018, 11:40:27 AM »
Last year we bought a circa 1900 house in metro-Boston with a fieldstone foundation and cement basement floor. The home inspectors were pretty thorough and didn't mention any problems with the foundation (we used these same inspectors on another house and there were foundation problems on that one). The foundation is about two feet thick, mostly big stones of 1 ft in diameter and larger and there's no standing water though there is some dampness in heavy rains along one wall.

Ok, so my question is the mortar in the basement seems crumbly and we have a lot of sand falling off of the walls. We can't have anything touching the walls or there's even more sand. No rocks are coming loose. Internet sleuthing leads me to believe this is the original lime-based mortar which is now almost 120 years old. The exterior foundation mortar seems solid still. Is that normal/expected for a fieldstone foundation? Or do we need to get it repointed? I did not grow up with fieldstone and I'm afraid if I get a mason out here they'll tell me to do it just because obviously that's in their best interest.

velocistar237

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Re: Repoint fieldstone foundation?
« Reply #1 on: April 04, 2018, 02:20:24 PM »
We live in a condo with a different fieldstone foundation issue. The downhill side has large cracks. The masonry company came today, and talking to the guy and seeing their work didn't give me any confidence that they knew what they were doing. It took our condo members forever to decide on a plan of action, so I don't want to put a halt to the work, but I wish I could just have done it myself. Sorry for the venting.

It looks like some fieldstone foundations do use sand below grade.

Quote
The typical fieldstone foundation wall was laid up dry.  Large supporting stones at the bottom, smaller stones at the top, stone wedges to stabilize. Lime mortar was only used above grade where there was no backfill to keep stones in place.... Gravel or sand backfill was used below grade.

We do have some material coming off of our interior foundation wall, but I always assumed it was just the coating someone had applied.

It could also be that the interior side of your foundation is old mortar while the exterior side has already been repointed, which would account for the difference in condition.

Opinions on repointing and mortar vary widely, and even though I'm not sure what's correct, I'm convinced that many masons don't do repairs correctly. Here is some more internet sleuthing for you.

Recoating crumbling basement walls - Chicago Tribune
Stone foundations - cause for concern? - Old House Web
Repointing Mortar Joints in Historic Masonry Buildings - National Park Service
LimeWorksUS Youtube channel

Let me know if you learn anything else or decide on a course of action.

littlebird

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Re: Repoint fieldstone foundation?
« Reply #2 on: April 05, 2018, 05:53:44 AM »
Thanks for the links, I'll check them out. I've been frozen with indecision on this and haven't made any moves. Some websites say to only replace with the original lime mortar, while others say more modern mortar is fine. Just thinking about it it seems like the type of stones would matter for that question. Like, ours are big chunks of granite and other hard stones, I think in the midwest they might be using softer stone. Man, old houses are so annoying!

Do you know what the cost will be for you? I think I'm afraid to get quotes for fear that it will be like 10k+. I'll let you know if I ever do anything about it, lol.

Fishindude

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Re: Repoint fieldstone foundation?
« Reply #3 on: April 05, 2018, 07:26:55 AM »
Sounds pretty normal to me.
If you don't have large gaps between stones, loose stones, or water seepage, I wouldn't worry about it.
These rock basements don't make very good finished living spaces if that's what you're after.  If you want to seal things up tight so the dusting stops it will probably require that you apply some type of a coating or sealer such as "Thoroseal" over everything.

velocistar237

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Re: Repoint fieldstone foundation?
« Reply #4 on: April 05, 2018, 09:06:23 AM »
Thanks for the links, I'll check them out. I've been frozen with indecision on this and haven't made any moves. Some websites say to only replace with the original lime mortar, while others say more modern mortar is fine. Just thinking about it it seems like the type of stones would matter for that question. Like, ours are big chunks of granite and other hard stones, I think in the midwest they might be using softer stone. Man, old houses are so annoying!

The hardness of the stones probably does mean Type S mortar won't hurt the stones, but it might hurt the old mortar. Hard mortar will probably hurt the brick on our chimney.

Do you know what the cost will be for you? I think I'm afraid to get quotes for fear that it will be like 10k+. I'll let you know if I ever do anything about it, lol.

It was $3,800 to repair two areas of the foundation, seal some open holes under a porch, and repair a chimney. If the cracks open up again, it will be another $10k to shore up the outside of the foundation. Even if we aren't doing the absolute best thing, at least it will be obvious if it starts moving again, and this bill was split among the condo owners.

Sounds pretty normal to me.
If you don't have large gaps between stones, loose stones, or water seepage, I wouldn't worry about it.
These rock basements don't make very good finished living spaces if that's what you're after.  If you want to seal things up tight so the dusting stops it will probably require that you apply some type of a coating or sealer such as "Thoroseal" over everything.

In my case, I use my basement for storage and as a shop area, so thankfully it doesn't have to look good.

I've seen mixed recommendations about sealers on old foundations as well.

littlebird

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Re: Repoint fieldstone foundation?
« Reply #5 on: April 06, 2018, 07:18:57 AM »
Fishindude, thanks for chiming in, that's reassuring! We have a tiny amount of seepage when it rains hard, more like damp spots than rivulets. Makes the basement humid in the summer though and we store stuff down there. We run a dehumidifier but there's only so much you can do. People in our neighborhood do finish their basements, but I think you'd have to be crazy to do it based on what I see in our basement. They must be full of mold. Mostly just don't want piles of sand and dust all around tracking up into the living space.

velocistar237, ok, $3,800 is less than I feared. I should just bite the bullet and get some quotes.



Sibley

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Re: Repoint fieldstone foundation?
« Reply #6 on: April 06, 2018, 12:42:56 PM »
Re the dampness - make sure your exterior drainage is addressed. You want water to drain away from the house, not sit next to the foundation.

robartsd

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Re: Repoint fieldstone foundation?
« Reply #7 on: April 06, 2018, 01:25:59 PM »
It doesn't sound like there is any immediate problem, so take your time finding someone you trust to do it right. I agree that looking at drainage issues around your foundation would be wise.

velocistar237

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Re: Repoint fieldstone foundation?
« Reply #8 on: April 16, 2018, 06:01:33 AM »
Here are some more links.

Stone Foundations - Good, quick summary about New England stone foundation issues and maintenance.

Capillarity—Small Sacrifices by Joe Lstiburek - Well-known building science expert on how damage to porous masonry units in historic structures can be prevented. This might not apply to fieldstone foundations, which are mostly composed of impermeable rock, but it's good to understand. It does apply to our brick chimney.

diychatroom thread - Decent discussion about someone actually getting the materials and DIY repointing their foundation using lime mortar. Tscarborough seems to be pretty knowledgeable.

velocistar237, ok, $3,800 is less than I feared. I should just bite the bullet and get some quotes.

They did less than we expected, and it's a pain trying to sort it out. I wish I had done it myself.

littlebird

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Re: Repoint fieldstone foundation?
« Reply #9 on: April 16, 2018, 08:07:29 AM »
Ugggghhhh, diy seems like such a huge project. Why is it so hard to find good contractors?