Repointing Limestone Foundation

While down in the basement the original foundation is in some dire need of attention. I am not quite sure what the best method is to repoint limestone is, I keep hearing not to use typical mortar mix. I have heard to use Type N, and then heard not to if it has Portland cement in it. Also, is there any bonding agent that needs to be put in the proper mortar mix for limestone? I contacted Quikrete, and here is what they had to say.

"We would not recommend using a Type S mortar for your soft limestone foundation due to its high compressive strength. It is preferable for the mortar being used for repointing or resetting stones back into place to NOT be stronger than the original mortar. If it is stronger, any settling of the structure will potentially cause the stones or the existing mortar, rather than the tuckpointing mortar or new mortar for resetting bricks into place, to crack. We would recommend consulting a local mason or engineer for the typical material used to repair these soft limestone foundations.

It's suggested using a Type O mortar for older restoration work which Quikrete do not offer. If you cannot find a pre-blended Type O mortar, you can mix 1 part Portland, 2 parts hydrated lime, and 7 – 9 parts of masonry sand. It may be possible to get away with using Mortar Mix Type N, but I would prefer the above option as a softer mortar for old restoration work but you will need to consult your local building codes."

I am just sort of confused because there are so many different options and everyone says something different, the fellow that said to just use Type N builds limestone chimneys, steps, foundations, etc, but I would like another opinion about simply using Type N, and if it would be better if I found something that utilized more lime. I have a lot of foundation repair to do outside of the house after I get the inside of this basement repointed and a perimeter drain installed (which I will save for another thread).

Thank you for your input!
I've attached a picture of the cellar walls/original house foundation.

 

I have been slowly repointing a fieldstone/rubblestone foundation that was originally pointed with lime mortar, circa 1890. I have been using Ecologic Mortar from LimeWorks www.limeworks.us and I have been pleased with the results. It is a lime mortar mix with no Portland cement in it. It's on the expensive side, but convenient. Of course, you could also mix your own, as they supply various NHL products. The pre-mixed stuff does achieve Type N compressive strength, but it's probably worth reaching out to them to see if it would still suit your needs, since lime mortar behaves a little differently.

I have been extremely impressed with the information they make available. I haven't had the occasion to actually speak with them, but my understanding is that they are quite knowledgeable. If the pre-mix wouldn't work for you, I'm sure they can steer you in the right direction. Mr. deGruchy does masonry restoration on historic structures in the Philadelphia area, so they see a lot of stonework.

And research as much as you can if you decide to go down the lime mortar route. I took on the project myself because most masons I spoke to said, "nah, Portland cement is fine, type S is fine, type N is fine," and it didn't inspire confidence. The ones who were familiar with lime mortar did major restoration projects and didn't want to be bothered with my humble home. So I learned as much as I can and taught myself.

 

Thanks for the response. Added up the price of what it would cost to ship one bag to me and it was $78. I am going to try contacting them and seeing if they have any more information.

Has anyone repointed using Type N? Or would I be much better off finding and mixing my own Lime mortar?

 

Hi,

I have an 1880s Fieldstone foundation. The previous owner told me he had been using Type N Mortar Mix to patch up loose, crumbling, sandy joints between the stones. Those are still intact and look fine. Over 8 years now.

That's what I'm going to keep using.

Any pre-blend with 1 part Portland, 1 part Lime and 5 or 6 parts sand will work.

Quikrete sells a Type N "Mortar Mix" that is exactly that combination and is perfect for bricks and stone bonding. Just add water and mix it into a doughy clay so it's easy to cram in between the stones.

My wall joints are only deteriorating below the soil grade, and only in patches, so I'm not doing full sections. Just anywhere I see yellow or tan loose sand crumbling.

Just make sure you use a MORTAR mix, not a MASON mix. And make sure it's Type N.

Type S is more for cinder blocks and floor slabs. I would not use that stuff to tuck point bricks or stone.