Mortar for repointing old stone walls?

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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
Is there a "correct" mortar for repointing old stone walls in a house?

The house is late 18th century, so the motar is not modern. Looks like clay to me.

I'm redoing the stove room from the inside. The plaster is down, so I'm ready to go. I plan to keep some stone faces exposed for aesthetic purposes.

The walls are about 18" thick.
 

semipro

Minister of Fire
Jan 12, 2009
4,168
SW Virginia
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gzecc

Minister of Fire
Sep 24, 2008
4,941
NNJ
You need to research this online. There is a specific motor you should use. I did this years ago at a friends house. The information is online.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
You can use modern mortar you just need to try to match the hardness of the rest of the mortar. I would recomend a weak mix of type o mortar. There are lots of people who will say you need to match the origonal mortar. But it really isnt necessary
 

Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
I won't be matching the original mortar. It appears to be mostly clay and has very little structural integrity left, if it had any to start 200+ years ago. I guess mostly I just want to hold what is there, in the wall.

These are indoor sides of the walls, so there won't be freeze-thaw issues. I'll read up on it, but I guess I won't just use that type-s bag I have sitting in the barn straight out of the bag.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
I won't be matching the original mortar. It appears to be mostly clay and has very little structural integrity left, if it had any to start 200+ years ago. I guess mostly I just want to hold what is there, in the wall.

These are indoor sides of the walls, so there won't be freeze-thaw issues. I'll read up on it, but I guess I won't just use that type-s bag I have sitting in the barn straight out of the bag.
No i wouldnt do that
 
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
You might PM @Ashful if you don't get a response. He's got an old stone house and probably knows.
Check this out: https://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm
I guess it depends on whether you're going for authenticity, matching what's there, or using something more durable than what's there now.
Good idea, but I doubt @Ashful would have spent the time required to do his own repointing, based on many of his posts. I don't have kids, so I have more time.
 

Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
You need to research this online. There is a specific motor you should use. I did this years ago at a friends house. The information is online.
Would you recommend Briggs and Stratton or Honda? I'm thinking I could just do it with good old fashioned elbow grease?

Or, were you referring to a specific engine (search) when doing my online research? I'm partial to Netscape, but I keep hearing about this googel thing.
 

Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
Oh yes, I have! Marking for response, later.
 

gzecc

Minister of Fire
Sep 24, 2008
4,941
NNJ
Would you recommend Briggs and Stratton or Honda? I'm thinking I could just do it with good old fashioned elbow grease?

Or, were you referring to a specific engine (search) when doing my online research? I'm partial to Netscape, but I keep hearing about this googel thing.
No good deed goes unpunished.
 
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
No good deed goes unpunished.
I appreciate your response and giving me the opportunity to to flex my feeble wit, but I think telling someone who posts to an online chatroom (which is doing online research) to do research online, might stretch the definition of "good deed". ;-)
 

Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
Somehow forgot to bring my iPad with me tonight, so short and curt typing on a phone.

Portland cement had not yet been invented in the 18th century. Mortars were generally some combination of clay, sand, and lime. Clay and sand could be usually found on site, so lime was usually the main expense. Depending on how rural or urban that place was when built, and I’m guessing it was fairly rural, the cost of transporting lime (by ox cart) could be downright prohibitive.

So, you will often find your bedding mortar is just whatever they could dig up in the back yard, some combination of clay and sand (hence the old slang, ‘mud’). They’d save that precious lime for making up a protective mortar that just provides a protective shell for the purpose of weather proofing, in the form of pointing or stucco, most often the latter. This is what makes 18th century construction so much more frustrating and fragile than 19th century, when they had and used Portland cement in their mortars. Any breach in the pointing or plastering of an 18th century wall should be repaired post-haste, to prevent washing out of the bedding mortar and shifting of the wall.

For repair, there are countless options. Most just use modern mortars, although this can cause damage to soft brick, and even some softer stones. Usually it’s fine on stone, though, as most stone is harder than any mortar. True conservationists use mortars of the time, mixing their own sand and lime, in various proportions that they’ve argued about for decades. Many others do a lime-sand mortar, with just a bit of Portland, to help it cure and stay better.

I have a book I can recommend on the subject, depending on how “in” to this you want to get. On my own stone house, I’ve just been using 3-4 parts brown sand with 1 part white Portland, which simulates the color of the original mortars (lime + local mud). In the few areas where I have brick (softer) I step to 4 parts sand + 1 part Portland. I used to be interested in conservation, but that was when I was younger and had more time, now I just want it done.

A lot of people today have put a lot more thought into this, than the half-illiterate masons of the time ever would have had the time for.
 
Last edited:

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Somehow forgot to bring my iPad with me tonight, so short and curt typing on a phone.

Portland cement had not yet been invented in the 18th century. Mortars were generally some combination of clay, sand, and lime. Clay and sand could be usually found on site, so lime was usually the main expense. Depending on how rural or urban that place was when built, and I’m guessing it was fairly rural, the cost of transporting lime (by ox cart) could be downright prohibitive.

So, you will often find your bedding mortar is just whatever they could dig up in the back yard, some combination of clay and sand (hence the old slang, ‘mud’). They’d save that precious lime for making up a protective mortar that just provides a protective shell for the purpose of weather proofing, in the form of pointing or stucco, most often the latter. This is what makes 18th century construction so much more frustrating and fragile than 19th century, when they had and used Portland cement in their mortars. Any breach in the pointing or plastering of an 18th century wall should be repaired post-haste, to prevent washing out of the bedding mortar and shifting of the wall.

For repair, there are countless options. Most just use modern mortars, although this can cause damage to soft brick, and even some softer stones. Usually it’s fine on stone, though, as most stone is harder than any mortar. True conservationists use mortars of the time, mixing their own sand and lime, in various proportions that they’ve argued about for decades. Many others do a lime-sand mortar, with just a bit of Portland, to help it cure and stay better.

I have a book I can recommend on the subject, depending on how “in” to this you want to get. On my own stone house, I’ve just been using 3 parts brown sand with 1 part white Portland, which simulates the color of the original mortars (lime + local mud). In the few areas where I have brick (softer) I step to 4 parts sand + 1 part Portland. I used to be interested in conservation, but that was when I was younger and had more time, now I just want it done.

A lot of people today have put a lot more thought into this, than the half-illiterate masons of the time ever would have had the time for.
Did you use just straight portland or a portland based mortar like type s type n etc?

The mortars have portland lime and a few other things mixed in. This makes it much better for setting or pointing masonry units. Straight portland should really just be used for concrete. Not to mention mortar made with straight Portland will be a real pita to work with compared to regular mortar.
 

Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
Did you use just straight portland or a portland based mortar like type s type n etc?

The mortars have portland lime and a few other things mixed in. This makes it much better for setting or pointing masonry units. Straight portland should really just be used for concrete. Not to mention mortar made with straight Portland will be a real pita to work with compared to regular mortar.

I forgot to say, straight lime mortars are often 1 part lime + 3 parts sand, and you can sometimes buy this as type L. No, I’ve not used it, because I’m doing mostly exterior work. If I were doing interior pointing, I’d like to give it a try. I probably should up my sand and add some lime, but I always seem to have Portland on hand, I’d have to go find lime. I don’t have trouble with tooling it, but yes, lime would make working it easier.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
I forgot to say, straight lime mortars are often 1 part lime + 3 parts sand, and you can sometimes buy this as type L. No, I’ve not used it, because I’m doing mostly exterior work. If I were doing interior pointing, I’d like to give it a try. I probably should up my sand and add some lime, but I always seem to have Portland on hand, I’d have to go find lime. I don’t have trouble with tooling it, but yes, lime would make working it easier.
You should try type n or type o you will find out pretty quickly how much nicer it is to work with. Type s would work and is more available but i like the softer mixes for old work. Modern brick or stone set with modern mortar we use type s.
 

gzecc

Minister of Fire
Sep 24, 2008
4,941
NNJ
I appreciate your response and giving me the opportunity to to flex my feeble wit, but I think telling someone who posts to an online chatroom (which is doing online research) to do research online, might stretch the definition of "good deed". ;-)
I've been in his exact situation and solved his problem by computer research. If it was that easy he didn't need to come here to ask. This is what we do here. We bounce questions off people who may have experience. A good deed is giving something away and asking for nothing in return. I gave away the way I figured out exactly which mortar to use.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
I've been in his exact situation and solved his problem by computer research. If it was that easy he didn't need to come here to ask. This is what we do here. We bounce questions off people who may have experience. A good deed is giving something away and asking for nothing in return. I gave away the way I figured out exactly which mortar to use.
The problem is there is no one answer. You should try to roughly match the hardness of the setting mortar. And absolutly need to be softer than the stone you are pointing. As long as you do that especially on interior work you can use whatever type of mortar you want with no ill effects. Outside you need to worry more about weathering and water infiltration so some are clearly better there.
 
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Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
The problem is there is no one answer. You should try to roughly match the hardness of the setting mortar. And absolutly need to be softer than the stone you are pointing. As long as you do that especially on interior work you can use whatever type of mortar you want with no ill effects. Outside you need to worry more about weathering and water infiltration so some are clearly better there.
Exactly, ask six masons, and you'll get at least four different answers. Go full traditional, lime and sand, and you'll be redoing it in several years. Go type O if you want something soft, that will actually set up in reasonable time, and hold up a bit better. If you want the color right, mix your own using white portland and brown sand, instead of the premix (which is always gray portland with yellow sand). They're all 3-4 parts sand to 1 part of portland + lime, adjust your portland to lime ratio for workability vs. wear and hardness.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Exactly, ask six masons, and you'll get at least four different answers. Go full traditional, lime and sand, and you'll be redoing it in several years. Go type O if you want something soft, that will actually set up in reasonable time, and hold up a bit better. If you want the color right, mix your own using white portland and brown sand, instead of the premix (which is always gray portland with yellow sand). They're all 3-4 parts sand to 1 part of portland + lime, adjust your portland to lime ratio for workability vs. wear and hardness.
We always mix our own. We just use off the shelf cements which are available in many different strenghts and colors including white. Most common mix used in our area is brown sand and grey mortar. Even back to most of the stuff in the 20s. Before that we use white mortar and mix the sand colors till it matches. I never use the baged stuff with sand in it already. It just doesnt work very nicely.
 
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Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
We always mix our own. We just use off the shelf cements which are available in many different strenghts and colors including white. Most common mix used in our area is brown sand and grey mortar. Even back to most of the stuff in the 20s. Before that we use white mortar and mix the sand colors till it matches. I never use the baged stuff with sand in it already. It just doesnt work very nicely.

Oh, bholler... how I wish you worked in my area. My favorite mason here is unfortunately color blind, if I don’t remind him every darn time he is here, I get a different color mortar every time. Half the time it’s gray, and my house is entirely done in brown. But I use him on big jobs, because he’s flexible, and is able to work around the carpentry and other work I’m always handling myself on such projects.

The reason I tossed out the white Portland comment above is that the OP is 18th century, so the pointing would have not had any cement. It would have been 1 part white lime with 3 - 4 parts whatever color sand they dug up from his back yard, usually brown, unless he was close to a sand mine. So, the white Portland with brown mason’s sand usually gets you in that color ballpark.
 

Dobish

Minister of Fire
Oct 26, 2015
2,038
Golden CO
when you guys are done there, can you come to my house?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,696
central pa
Oh, bholler... how I wish you worked in my area. My favorite mason here is unfortunately color blind, if I don’t remind him every darn time he is here, I get a different color mortar every time. Half the time it’s gray, and my house is entirely done in brown. But I use him on big jobs, because he’s flexible, and is able to work around the carpentry and other work I’m always handling myself on such projects.

The reason I tossed out the white Portland comment above is that the OP is 18th century, so the pointing would have not had any cement. It would have been 1 part white lime with 3 - 4 parts whatever color sand they dug up from his back yard, usually brown, unless he was close to a sand mine. So, the white Portland with brown mason’s sand usually gets you in that color ballpark.
I know that i was just pointing out that you could just get white type n or o and get the same color with more appropriate properties.
 

Ashful

Minister of Fire
Mar 7, 2012
16,552
Philadelphia
Oh... got it. I wasn’t aware you could buy that pre-made.