[Nivk]

I'm looking for some advice on how to best repair the old stone foundation of my house. The place was built in 1870 and the mortar between the stones has turned to dust in places. A previous owner tried to "repair' this problem using insulating spray foam for some reason :furious:, though I kinda doubt that's helping to support the house...

Anyway, i've been vacuuming out the dust and repointing with new mortar. So far I've only completed a portion of one wall. I was recently told by an acquaintance that I should be adding lime to the mortar, but so far I haven't done so. At this point I'm using quickcrete mortar mix No.1102 type N (which says on the bag it is appropriate for tuck pointing stone). I chose this because it should not be as unforgiving as a type S mortar which could damage the natural stone and because of what I read here, http://www.oldhouseweb.com/how-to-advice/stone-foundations-cause-for-concern.shtml, which said it should be ok for interior walls even though it is cement based:

"Inside, it's a different story: Pre-packaged mortar mix can be used for the repointing and also the recoating. Simply follow the mixing instructions on the bag of mortar,troweling the mix between the stones and finishing with a complete coating."

Is is necessary to add lime to the mix? Can I add it to the mix I am using or do I need to mix something from scratch? If so how much lime should I add and where do I get it? Also what is the reason for adding lime anyway?

The image below shows the problem (the gaps in the mortar go much deeper than can been seen in this photo), and my attempt at repairing it (top left). Thanks in advance for any advice.

 

[Daniel Holzman]

The original mixture for mortar was worked out by Vituvius of Rome, and consisted of one part lime, one part sand, and one part water. This mixture worked very well for about two thousand years, and still works today. However, around 1900 masons began using portland cement based mortar, which is stronger, but is more brittle than lime based mortar. Many masons who specialize in old houses will tell you that modern portland cement based mortar is too strong and inflexible, and damages brick or stone.

If you are planning to use portland cement based mortar, there is no reason to add lime. If you are using lime based mortar, there is no reason to add portland cement. In either case, you need to follow the mixture directions on the bag. And the mortar adds little strength to the stone foundation, it is really there just to keep the stones together. This is quite different from concrete, where a substantial part of the strength is derived from the cement.

 

[Tscarborough]

Actually, if you do a search here for "lime mortar" and "foundation", you will find complete instructions for what you need to do. What you are currently doing is just about as bad as the spray foam, if not worse.

 

[Nivk]

Well fortunately I haven't gotten too far, and there is already plenty of cement patches from even earlier repairs. I had been having a hard time finding a straight recipe for lime mortar mix online, but I just came across this from the www.gsa.gov page on historic preservation:

For Limestone (ASTM C270 Type "N"):

1 part portland cement
1 parts lime
4-6 parts aggregate
Enough water to form a workable consistency

I will switch to this using sand as an aggregate, once I find a source for hydrated lime around here.

 

[CplDevilDog]

Just returned from Ireland and got to look at a few stone walls done in lime mortar. Some as old 800 AD. Amazing.

So the Portland Cement is hard and brittle, while the stone is soft and flexible? Leading to cracking of the joint quickly, correct? Assuming Lime Mortar is hard to come by, would Type S or Type K Portland Mortar be more appropriate to this application?

I believe they have lower Portland concentrations and therefore, a higher tensile strength.

 

[Tscarborough]

I would limit the portland to less than 20% by volume of cementious materials (lime and portland), and 10% would be even better. You only need the portland to allow for an initial set, as the lime mortar requires some time. The mix above is NOT a lime mortar, it is Type N portland cement mortar, and is not suitable for this application.

 

[jomama45]

As usual, Tscar is right on the money on this scenario. Lime mortar allows moisture/vapor to pass through the wall as it enters from the exterior. Patching the inside with a less permeable mortar will only trap that moisture in the wall, further eroding the remaining lime mortar in the wall.

 

[Nivk]

Ok, so this is starting to make sense to me. At first I thought it wasn't a big deal for stones since they are harder than brick and wont be damaged by the mortar, but it sounds like its less an issue of face damage and more of an issue of moisture permeability.

From what I had read in the gov't restoration guides the softer (high lime) mortars are critical for brickwork that is exposed to the elements, but for a stone wall that is on the interior side of a basement it seems like the harder mortars would be less of a problem. But this does not address the moisture issue.

Anyhow, what you are describing sounds more like a type K mix, or 1 part cement to 3 parts lime to 10 parts sand. But even softer since the type K is still 25% cement. So would it be ok to adjust this recipe to: 1 part cement to 6 parts lime to 10 parts sand, so it is less than 20% cement, or do I need to adjust the aggregate content as well?

Also, how do you mix these mortars? Can I just combine volumes of portland cement, hydrated lime, and sand with water, or do I really have to soak the lime and make a putty first?

 

[Tscarborough]

It is acceptable to mix 1 part lime and 3-5 parts sand (by volume, always by volume).

For a blended mortar, you can use Type S lime straight from the bag, for lime mortar, the lime needs to be hydrated. Gently cover with water and keep covered with water for at least 2 days, then pour off (and save) excess water and the lime is ready to be used. As long as you keep it covered with water it will remain in a usable condition. It is extremely caustic when wet, so wear protection.

 

[Vincer]

Home Depot and Lowes here (in the San Francisco Bay Area) carries 50lb bags of lime in the cement mix section.

 

[Nivk]

Alright... I'll look for some lime and give it a shot this weekend. Unfortunately they don't even know what it is at the local Lowe's/HD. I'll call around to some masonry supply places and see what I can find. It must be sold somewhere in central PA. There's a factory that produces the stuff right down the road.

 

[Tscarborough]

Make sure it is Type S lime, not ag lime or the lime known technically as $hit-house lime.

 

[Vincer]

Alright... I'll look for some lime and give it a shot this weekend. Unfortunately they don't even know what it is at the local Lowe's/HD. I'll call around to some masonry supply places and see what I can find. It must be sold somewhere in central PA. There's a factory that produces the stuff right down the road.

http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

Home depot, type s lime

 

[Nivk]

I found the lime at the local true value, and mixed up a test batch of mortar as suggested above with portland cement composing 20% by volume of cementious materials. It was like a type K mortar with less cement. (0.75 cement : 3 lime : 10 sand). It looks like it did the trick, but I have 2 concerns about it:

1) it took quite a bit more water to get to a workable consistency - as compared to the quickcrete type N mortar

2) it is taking quite a bit longer to dry and is noticeably less hard than the quickcrete stuff.

I assume softness is to be expected because it is a softer mortar, and since more water went into the mix it makes sense that it is taking longer to dry, but I was just hoping to confirm that this is normal and I didn't screw something up. Thanks.

 

[fieldstone]

Nivk, how did you make out with your lime mortar? I've got a lot of pointing on my to do list...

 

[Nivk]

Oh yeah... I meant to come back and give a final update. The lime mortar took a bit longer to dry (it was also pouring rain that week so the basement walls were damp). But once it dried it was nice and hard. It is a bit softer than the quickcrete mortar, but I guess that's the point. Good luck with your pointing.

 

[tarzanbites]

Mr. Scarborough,
I have a quick question for you. You said: "For a blended mortar, you can use Type S lime straight from the bag, for lime mortar, the lime needs to be hydrated. Gently cover with water and keep covered with water for at least 2 days, then pour off (and save) excess water and the lime is ready to be used. As long as you keep it covered with water it will remain in a usable condition."
I plan to use as you recommend up to 10% portland to help with an initial set. Is this considered a "blended mortar" ? The lime at the Home Depot in my area is Type S hydrated. Is this different than placing lime in a bucket for several days with water?
I've got a big project and am completely new to this. Thanks for you advice.

 

[SimonFromKansas]

Is that all it takes to get hydrated lime? I've been working for years in France (where i learned the masonry trade), and I got back to the states expecting to be able to find NHL-3,5 but it's damn near impossible.

It is acceptable to mix 1 part lime and 3-5 parts sand (by volume, always by volume).

For a blended mortar, you can use Type S lime straight from the bag, for lime mortar, the lime needs to be hydrated. Gently cover with water and keep covered with water for at least 2 days, then pour off (and save) excess water and the lime is ready to be used. As long as you keep it covered with water it will remain in a usable condition. It is extremely caustic when wet, so wear protection.

 

[NHughes]

old stone building

I too need to find out what type of cement to use to repair my old stone home I purchase last year. The stones in the basement/foundation is turning to powder. I need something that does not absorb water. Can I order this type of cement/mortar?

 

[elwoodzulu]

so what is the bottom line ...I have a 1850 cape in Mass very wet most of the old lime mix is gone with large gaps in a 6 foot high field stone foundation still working on gutters and french drains to help with the water problem ....over the years the stone has been moving a bit ...house is on side of hill facing down.
the old restore guys seem to say lime mix "This OldHouse" says S mix with Bonding additive
is there a common agreement here ....help I want to start soon
GREAT CHAT !!!