Stone foundation repair question

[Brian Elfert]

My grandparent's house had a stone foundation. They had an issue with a section of the wall and they just had it replaced with a concrete block wall. The basement was constantly wet and pretty much unusable besides the furnace and water heater. In their case they just wanted a basement that wasn't going to collapse for the least amount of cost. They didn't want to keep the stone for the looks.

[Thomas McCurnin]

As the owner of a wilderness cabin with a rustic stone foundation, I agree with Jim that trying to fix that single stone is probably a fool's errand. A better approach is to try to stabilize the foundation with Type M Mortar, chicken wire, No. 4 rebar above and below the miscreant stone. I do like the idea of a header of sorts which could be as easy as Number 4 rebar covered with Mortar.

[Zachary Hoyt]

I figure it must be time for a followup on this thread, since I finally completed the work on the foundation yesterday. I drilled 4 holes in the sloping rock and tried to break it with wedges and shims. I hit the wedges with a 40 oz hammer for a while, and then a 16 pound sledge (not that I could get a good swing, but still, I hit them pretty hard) and nothing happened. It took about an hour to drill each 3/4" hole to 4" depth with my little hammer drill.

I finally got the wedges back out of the holes and put in rebar in the holes, and also laying across the top of the sloped part and built the wall on that. I'm not proud of the result, but it's not much worse looking than the other walls of the basement, and they have held up the house for over 100 years and through being flooded, so I hope it will be okay for a while. Eventually the rebar will rust through and it will probably collapse again, but I hope that won't happen for 30 or 50 years. There were two of the biggest stones that fell from the wall that I was not able to break with the sledgehammer, though I did make one of them smaller by chipping off bits. Some of the other big stones broke into nice chunks after only 4 or 5 hits. These rocks seemed to have a grain along which they would break, and the ones that wouldn't break seemed to be going all over the place, at least the bits I broke off seemed quite random.

Thank you all for your advice. I wish I had been able to do a better job, but time was running short. I put more than 3/4 of a dry ton of mortar into the wall, and tried to follow the rules of putting rocks where they would stay without the mortar and leaving a flat surface on top of each rock.

[Frank Pratt]

It took about an hour to drill each 3/4" hole to 4" depth with my little hammer drill.

If you'd have rented a rotary hammer, it would have taken only a few minutes per hole. The little 'hammer drills' are not the real deal. They are more of a noise maker than a hammer drill.

[Zachary Hoyt]

Yes, I know, but I would have had to drive 30 miles each way to rent and return the drill, plus paying for the rental, so it didn't seem worth it. I also wondered if the more aggressive hammering would shake more stones loose from overhead, and if I squashed their expensive drill I would have to pay, besides any ensuing medical expenses.

[Tom M King]

I'm surprised that stone was that hard. With softer stone, you have to drill deeper holes, or the wedges just spall the hole bigger. Some need more holes in the row too. Granite is the only stone I know of that you might get by with a 4" deep hole. There is no hard and fast general rule. I use the largest size SDS-Max drill, and for holes no bigger than 5/8", it's not much different than drilling wood.

[Zachary Hoyt]

I only got the wedges about 2" into the holes, so they weren't bottoming out. They did spall chips out around the tops of the holes, but even so they wouldn't go down far. I probably could have broken it with more holes, but I gave up and took the easy way out.

[Maurice Mcmurry]

Dressing stone in a wall made of undressed stone just seems silly to me. I admire your fortitude.