# What mortar for tuckpointing old sandstone foundation



## BillBill (May 27, 2014)

Here is some background:
The house has a 100+ year old sandstone foundation. At some point it was covered with some type of mortar and 1 to 2 coats of point. That covering is now falling off or can easily be chipped off in many places. Behind it, the "joints" between the sandstone are just large gaps, holes, and caves filled with sand. I was thinking it might be a good idea to remove the sand and fill it in with mortar.

Questions:
1) Should I remove the sand and fill it in with mortar?

2) What mortar should be used? Everyone I talk to says to just use the Quikrete mortar mix (I believe this uses a masonry cement that is equal parts Portland cement and Lime). But many online advice-givers warn that any cement in the mix will counteract the permeability of the lime, making it not breathable and resulting in horrible damage to sandstone. So I was thinking I might try just mixing up some sand and lime as recommended here, but I have no experience with the mixing and curing process.

3) After tuckpointing, can the wall be painted with a latex paint? Or will any paint make the wall not breathable and cause damage?

Thank you for any ideas!

Bill2


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## Tscarborough (Mar 31, 2006)

If it was originally lime, it needs to be lime to repair it. As you can see, the cementious mortar used to "repair" it in the past has made it worse, if not destroyed it beyond anything but full reconstruction. It might be worth your money to have a professional look at it for recommendations, even if you end up doing the actual repair work yourself. You need a very specific type of professional though, not just a mason or even a structural engineer. You need a masonry restoration contractor.


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## stuart45 (Jun 20, 2009)

For external pointing I normally use a mix of NHL 3.5 lime (one part) with sharp sand and building sand 50/50 (3 parts).
It needs 20 minutes in the mixer, left for 20 to fatten up, and then mixed for a couple more minutes.
Finish with a flush joint, and then hit the joints with a churn brush the next day to expose the aggregate.
Keep the sun and rain off the joints for a while.


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## stonecutter (May 23, 2014)

And whatever you do, don't paint the stone.


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## Tscarborough (Mar 31, 2006)

Right, you CAN however lime wash it.


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## BillBill (May 27, 2014)

Thank you everyone!

I cannot get my hands on any hydraulic lime. The only lime I can find around here is what they call Miracle Lime (hydrated, type S), and the masonry supply stores carrying it recommend it to be used in a mix with cement (even when I asked specifically about old sandstone and breathability).

Also, the GSA "Historic Preservation" guidelines for Preparing Lime Mortar For Repointing Masonry (using type S hydrated lime) advise using cement in all of the mortar mixes that they have listed - the highest lime to cement ratio given is 3:1 for working on historic masonry set in lime mortar:
http COLON //www DOT gsa DOT gov/portal/content/111682

Can the Miracle Lime be used without cement? If I use 3 lime to 1 cement, is that at least better than using a mix with equal parts lime and cement, or is it just as bad?

I did find a website where a guy describes making a mortar with just Miracle Lime and sand (similar to the GSA guidelines, except he lets the lime putty sit longer and adds no cement):
http COLON //faa-engineers DOT com/~mjgundry/blog/index.php?entry=entry070620-195920
Maybe I will give that a try.


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## landfillwizard (Feb 21, 2014)

Contact a farm supply store and ask if they have hydrated lime. We use to get it for changing the pH of soils.


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## stuart45 (Jun 20, 2009)

BillBill said:


> Can the Miracle Lime be used without cement?


It can, but ideally you need a pozzolan such as brick dust,because non hydraulic lime relies totally on carbon dioxide to harden and cure. 
If used internally this is OK, but if used for external pointing the weather often gets to it before it has a chance.That's why NHL is normally used outside.


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## Tscarborough (Mar 31, 2006)

Yes, in the US we do not have a native hydraulic lime, so you have to either pay exorbitant rates for French NH lime, or use Type S hydrated lime and something to give a quick set that will also allow the lime to breathe. You can order some pozzolans online, or use brick dust if you have a saw and some brick. In any case, use less than 10% by volume of cementious material, preferably less than 5% (pozzolans will have their own ratios but still in that range).


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## BillBill (May 27, 2014)

landfillwizard said:


> Contact a farm supply store and ask if they have hydrated lime. We use to get it for changing the pH of soils.


I can get Miracle Lime, which is Type S hydrated lime. Is there any advantage to getting hydrated lime from a farm supply store instead? I have heard that lime from farm supply stores may or may not be usable for masonry, depending on their source.

Thanks again everyone! I now have a slightly better chance of not doing a terrible job, which is all I can hope for.

Bill2


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## Tscarborough (Mar 31, 2006)

Farm lime will have to be slaked, but it will probably be better in the long run. If you want to do it soon, use the bagged lime, if you have a couple weeks to slake the agricultural lime use it.


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