Sandstone Foundation

[Kashka-Kat]

My house is built of concrete block sitting on top of sandstone rock foundation - which Ive ignored for a long time but now I see is obvious need of repointing at least in some areas that are exposed (above ground). On one side of my house, theres a sidewalk that butts right up to it, so I'm just going to caulk that seam between the walkway and house....and assume all is well underneath the sidewalk.

As far as the rest of it goes, theres maybe 15-20 ft that has missing mortar , rest looks ok/intact. I assume I proceed by digging down to see if mortar is OK below ground level. Any ideas on what to expect? I dread the possibility that it might be in bad shape all the way down.

Havent found much about sandstone - except for this: https://www.gsa.gov/portal/content/112998

It says Type O for sandstone not exposed to elements, Type N if it is. If its exterior, but underground, do I assume its NOT exposed? or is it?

Any tips or pitfalls to be aware of - its kind of scary doing something new - esp if it involves taking apart something and possibly opening a can of worms.!

[Seabornman]

I think you'll find the actual repointing fairly easy. After you've cleaned out the joints (try to scrape out any loose mortar), mix a small batch of mortar, pull up a little on a trowel, and push the mortar off of the trowel with a long narrow pointing trowel (or make your own by modifying a cheap trowel). Get the joint how you want it by tooling, let it set a little, then brush off the stuff that gets on the stone. Finding the right mortar might be harder. See https://www.nps.gov/tps/how-to-preserve ... joints.htm When I repointed a limestone barn wall I just took masonry mix and added sand to make it weaker. You may need to buy a lime-based mortar for your project.

[Gothichome]

Kashka-Kat, this is what I use for the pointing of Gothichome. Works great. A bit expensive though, the 22kilo (50lbs) bag cost me $50 Canuck bucks. It can also be used to fill lager voids in the mortar with the addition of play sand or any sharp sand. The bricklayer fellow who suggested it even uses it as bedding mortar for soft brick restoration. But for pointing, mix it right out of the bag. Only down fall for you might be finding it, it is made in Quebec. I get it at the local brick yard.

[Kashka-Kat]

Gothic, what is it that you use - I could not see link? Is your house sandstone as well? Since sandstone is softer (I think?) than regular old rocks from the back 40 (eg limestone, granite, etc) I want to be sure that Im using the right mortar for it. thx

[Olson185]

We went to an estate sale a few weeks ago and I noted the sloppy re-pointing job done to the porch skirt. At first, I thought someone had tried painting the mortar, with a too-wide brush, in that the bright white of the new mortar overlapped the bricks. Also, the mortar was flush and level with the bricks. Just sayin', there are ways to not do it.

As for the type of mortar, the ratio of sand to lime to cement seems to be one of those things every professional has a different formula. Some say omit the lime altogether. The only thing everyone (incl. me) agrees is that the mortar should be weaker than the material around it. How to get that is easy; what to use is the confusing part.

[Sow's Ear Mal]

Never omit the lime. Most preservation mortars omit the portland. Portand cement in a mortar creates a vapor-impermeable material, and is harder than most natural stone. The result is that moisture will have to escape through the stone or brick itself, and will cause spalling, especially in a freeze/ thaw climate. I am not an expert but I have been researching this for my own limestone house. Check out these guys, they know about mortar and sandstone-- http://www.limeworks.us/home.php

[Gothichome]

Kashka, sorry, here is the link.
http://www.daubois.com/en/restomix.php#.php
The link to its material data sheet on the right side of the page

[DRJR]

As for the type of mortar, the ratio of sand to lime to cement seems to be one of those things every professional has a different formula. Some say omit the lime altogether. The only thing everyone (incl. me) agrees is that the mortar should be weaker than the material around it. How to get that is easy; what to use is the confusing part.

This is very true. We had a different formula for most jobs depending on the requirements.

The only time we would omit lime is in sea walls. Those were done with a very strong mix of portland cement.

[Kashka-Kat]

Sorry to vent, but heres one more thing I'm totally stalled on. Either I'm finding "how to" advice that says slap on any old thing regardless of portland content, vs. ones that say "have your mason get the mortar tested."

"My" mason - LOL.

I just cant understand why to test it. How do we know the old mortar was the correct one? Just because its old doesnt necessarily make it right. There were probably a bunch of geezers all with different opinions arguing about it then, just like now. Only difference is they had no internet so they had to do it face to face.

Why cant I just identify my rocks (sandstone) and just get a good answer re: what mortar should be used on it?

Oh btw all this repointing will be totally below grade - not visible. So while I tend to be neat and obsessive, Im sure it wont be the neatest job in the world.... but it wont be seen so should be ok no?

PS Thx Gothic, I will contact the Limeworks guys - if its below grade though is it going to matter since there wont be same freeze/thaw thing going on....?

[Kashka-Kat]

Wait a minute! Just went back and read my orginal post & the link to gsa/ university of Vermont - they say Type O if not exposed to weather. So depending on what the Limeworks guys say, I think I'll just go with that.

Now here's an interesting discussion on type o including how to mix it and proportions:

"But, to get to the problem at hand, the basic principle, repeated over and over again in industry literature, is that the mortar should not be harder than the bricks. You have a nineteenth century house. If the bricks seem light and porous and the mortar is soft and easy to rake out, I would recommend Type O portland cement/lime mortar. Get a bag of portland cement and a bag of hydrated lime. Collect 12 equal-sized containers (16 oz. drink cups would work). Fill nine with masonry sand, two with lime and one with portland. Mix these together with water and you'll have enough mortar to keep a couple of masons busy tuckpointing for two hours--the recommended board life of masonry mortar. The mix, by the way, will be as smooth as butter and very easy to work with."http://forums.finehomebuilding.com/breaktime/construction-techniques/why-do-masons-hate-type-o

What is masonry sand?