# Mortar for limestone - HELP!



## AverageJo

We have a limestone basement and some of the blocks are loose. We need to find a recipe for the proper mortar to use in limestone. We've been told that a cement mortar will break the limestone blocks as it expands at a different rate and is too 'hard' and will cause more damage. But nobody knows exactly what to use. Anyone out there that can help us?


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## Pelenaka

AverageJo said:


> We have a limestone basement and some of the blocks are loose. We need to find a recipe for the proper mortar to use in limestone. We've been told that a cement mortar will break the limestone blocks as it expands at a different rate and is too 'hard' and will cause more damage. But nobody knows exactly what to use. Anyone out there that can help us?


Contact a preservation group that is geared to the era that your home was built in. They should be able to point you in the right direction. 

Have you searched This Old House website?


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## big rockpile

AverageJo said:


> We have a limestone basement and some of the blocks are loose. We need to find a recipe for the proper mortar to use in limestone. We've been told that a cement mortar will break the limestone blocks as it expands at a different rate and is too 'hard' and will cause more damage. But nobody knows exactly what to use. Anyone out there that can help us?


I've always used Cement Mortar on Brick,Block and Rock,never heard of it being a problem??

big rockpile


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## Bearfootfarm

You may be able to get some answers here:

http://www.quikrete.com/ContactUs/Main.asp


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## T-Bone 369

There are different types of mortar mix depending on the application rated by the strength of the mix. Types S and N are the most common - N is the most common as it is a good mix for almost everything in new construction, S is a little stronger and is used for block foundations. The problem you get into when your doing repairs is the old mortar will be weaker than the new and will not have the same amount of give. As the wall expands and contracts it can create cracks that allow water into the wamm and can cause the face of the brick (or stone in your case) to sluff off. You see this on flues often where the brick faces popping off. There are several other types of mortar designed for repair and tuckpointing - O and K. We have used O several times on repairs but you will have to go to a masonry supplier to get it. Both are weaker strengths and not suitable for load bearing new construction but also have more "give" so they are less prone to cracking in repair work. 

What ever you do I would suggest that once the work is done you get a good waterproofing sealer and apply (skip the Thompson Water Seal - it is pretty poor). Ask the supplier where you get your mortar and see what they suggest. We usually use Thoroseal - it's not cheap but will last for years. We usually apply it with a pump up sprayer starting at the top of the wall and soaking it as we work down. Stone has a lot of places that can catch water and this helps to keep it out. 

Good luck with your project and holler if you have any other problems.


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## dirtman

I have laid up a lot of stone walls with out any problem but  if I were worried about expansion at different rates and you aren't doing a large area of repair I'd mix up a batch of premium thinset. Make it stiff. It will be much more flexible than regular mortar.


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## AverageJo

Thanks for all your help! I didn't realize that there were so many types of mortar/cement. Cool. Now to see just who has what and what I can get without placing an order. I guess if I can't get O or K, I might just try the thinset. Whatever we do, I'll be watching it to see how it fares. Again, thanks.


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## Rootdigger

You may want to look into a lime based mortar, it still holds a lot of roman structures together to this day. Wish I could help for the mortar but all my research has been on lime plaster for my walls, What I do know is that in the multi year curing process is turns back into limestone.


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## Farmerwilly2

Look up lime mortar or lime putty. 

I take that back, first thing would be to figure out what the origonal builder used. Check the site for the bricklayers assoc. 

I suspect if it is an old building it was likely a lime/sand mortar for stone work. This might be out of the skillset for most folks (if the stone is loose) requiring the structure to be braced before removing and cleaning stone for repair.

Most things can be done. Comes down to if it is worth the price to do it or not.


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## dirtman

We add about 2 shovels full of hydrated lime to a wheelbarrow full of the mortar we use for the scratch coat of our stucco. It makes the mix spread more easily but it also makes it less durable so it doesn't go into the finish coat.


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## T-Bone 369

You guys do realize that mortar is a mix of lime, Portland Cement and sand. Many old buildings were layed using what they called "Lime Mortar" - it contained little if any cement. It also did not weather well. The O and K type mortars have a higher amount of lime in the mix but still enough Portland to be durable. Years before premix mortar (not the crud with the sand already in it but the 90lb bags you add the sand to) when you mixed you used seperate sacks of Portland and lime along with your sand. I did this once many years ago - we were working under an architect that just didn't trust premix. It was really hard to keep consistant mixture especially on smaller batches like you would use for tuckpointing.


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## Farmerwilly2

Yep, the portland mortar is stronger, but lacks the flexibility of the old lime mortars which, while less durable, allowed for more flexing. It also takes a lot longer to cure, up to a month or more. This is why it's beneficial to find out what you're working with. As for durability, I'm betting there are still buildings in the 13 first colonies that still have lime/brick walls standing.


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## AverageJo

So, if I'm understanding this, can I get a premix bag of portland cement and just add more lime to it? This is sounding like I might be able to do it if I can't find anyone else. We're not among big populations of old houses so finding an expert is few and far between, and they aren't telling either!


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## Dry Bridge

AverageJo said:


> So, if I'm understanding this, can I get a premix bag of portland cement and just add more lime to it? This is sounding like I might be able to do it if I can't find anyone else. We're not among big populations of old houses so finding an expert is few and far between, and they aren't telling either!


I suppose you could do that...but as others have indicated, that's putting a bandaid on the situation. NOTHING last forever, but if you try to stick to a particular method what you do may outlast you...trying to combine methods will probably yield unfavorable results.

Paul B.


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## Dry Bridge

Just to follow-up, the following link provides additional details/information when about the challenges when using improper mortar mixes: 

http://www.oldhouseonline.com/a-short-course-on-historic-mortar/

Paul B.


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## Wanderer0101

AverageJo said:


> So, if I'm understanding this, can I get a premix bag of portland cement and just add more lime to it? This is sounding like I might be able to do it if I can't find anyone else. We're not among big populations of old houses so finding an expert is few and far between, and they aren't telling either!


Yes, you can. I've mixed it one bag of lime with one bag of portland plus sand and that worked pretty well. It seems to be a little harder on your hands than a regular masonry mix.


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## Pigeon Lady

Average Jo, This guy was very helpful to us when we were researching this subject. We are about to begin repointing our 100 year old chimney with lime mortar.

LimeWorks.us - Ecologic Mortar

We have a friend in England who is a builder in the restoration trade. He was telling us there has been a huge swing back to the use of lime mortars as many ancient buildings have suffered untold damage from the use of modern materiels in their past restorations.

Good luck with your project.

Pauline


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## Evons hubby

AverageJo said:


> We have a limestone basement and some of the blocks are loose. We need to find a recipe for the proper mortar to use in limestone. We've been told that a cement mortar will break the limestone blocks as it expands at a different rate and is too 'hard' and will cause more damage. But nobody knows exactly what to use. Anyone out there that can help us?


I have laid up quite a bit of limestone over the years... I have always used regular old brick and block mortar. (cosmortar) Never had any trouble with it.


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## pipedreamer

Out here in texas we use a combination 1/2 Portland cement and 1/2 mortar mix ,very sticky very strong bonding ,make sure to wet the rock first.for a 100% bond


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## o&itw

Don't expect the lime mortar to be "waterproof" but if you have a "soft" limestone basement it is the way to go. This type of masonry has to move a bit with temperature and moisture. Regular brick mortar is too hard and will crack away from the edge of softer limestone. 

There are multiple books written that explain this and why 400 year old stone buildings are still in good shape while 60 year old stone walls built with straight Portland-style cement are falling apart.


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## AverageJo

Thanks again for everyone's input. I've really appreciated it. Hope it might help someone else, too, that might be looking at fixer-uppers.


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## mlzeigler

Average Jo,

I know exactly what you're talking about when repairing or restoring limestone as I had this same issue with our barn foundation. You are correct in that there is a special mortar to use for limestone. Cement will dry out the limestone. Typically, it's a particular mixture of portland, lime and sand. I utilized an expert in this field who has over 50 + years of experience with limestone work. Last summer (2011), we restored the entire inside limestone foundation of our barn. It looks immaculate. We're completing the outside this summer. I would highly recommend using this individual for your project unless you really want to do it yourself. I worked with him on the project. I also live in northwestern Illinois so you could see our barn. If interested, please contact me. Good luck. Thanks Mark. 815.713.1390


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