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Thread: Stone foundation repair question

  1. #1
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    Stone foundation repair question

    I have run into an unpleasant surprise when I started repairing the collapsed foundation wall at the house I am working on, and I'm hoping that someone here may have some advice about what to do now. The wall I am working on is about 12 feet long and 6 feet high, and close to 2 feet thick. In the middle near the bottom of the wall there is a huge stone which has a pretty smooth top set at a slope of about 30 degrees. I dug under the stone and around it and tried to roll it forward so the sloping face would become vertical, but it would not move with a 4-1/2 foot crowbar or an 8 ton jack. I am thinking about several possible ways to repair this wall, but they may all be bad ideas for all I know.
    1. Make a buttress of stone in front of the sloping stone
    2. Drill into the stone (with a hammer drill?) and put some pins in, sticking up.
    3. Lay some rebar across the stone, with the ends buried in the new wall on either side
    4. Make a header over the sloping stone with some heavy steel, supported on either side on the new wall.

    I'll be grateful for any ideas or guidance. I had thought it would just be a matter of removing the rubble from the collapse and cleaning up and re-laying the stone, but I wasn't expecting this extra wrinkle.
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    Last edited by Zachary Hoyt; 05-22-2022 at 2:17 PM.

  2. #2
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    I would try option 2 combined with option 3. Concrete bonding adhesive and type S mortar should allow you to make a flat top on that rock. You could make a small form to pack mortar or concrete against. Your project is quite an undertaking!
    Best Regards, Maurice

  3. #3
    I honestly haven't a clue on how to help, but I had a hard time figuring out what I was looking at, so I added some light to the pics, maybe it'll help others help out?

    r1.jpg r2.jpg r3.jpg
    ========================================
    ELEVEN - rotary cutter tool machines
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    THREE- make that FOUR now - fiber lasers
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  4. #4
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    I would cut a flat spot on top of that stone with a hammer drill, and wedges and shims, and relay the wall. When laying stone, it's best to leave your best flat spot on top so the next layer has a better chance of finding somewhere to rest. The reason is obvious here. Drilling the hole for that pipe took out a good section of that wall just because they put the sloped side up.

  5. #5
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    Thank you all very much for your advice. I have ordered 7 sets of wedges and shims and will give that method a try. If I can knock off the front or make a ledge I will be very pleased, and splitting stone will be a useful skill for later. Can I use a regular masonry drill bit or do I need a special bit to drill stone? I meant to ask that before.

  6. #6
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    An SDS Max type hammer drill should drill through the rock with no problems. Like said above if you drill several holes you should be able to knock the top of the stone off. A horizontal top on the rock with the remainder of the drilled holes should make a very high friction surface to hold what ever is put on top of it.

    I have drilled through several rocks with a hammer drill and it usually goes pretty easily. I have always drilled vertically and the weight of the drill is usually about right to supply the needed down force. I like to use a trickle of water the keep the tip of the drill cool and wet the dust to keep it from blowing up into a rock dust cloud. You should wear a mask while drilling rock! The dust from drilling is quite fine, pretty easy to inhale and the drilling will kick it up into a cloud. The Bosch SDS Max drill bits are of good quality and last quite long as well as cutting quite well. The 4 cutting surface bits (two straight lines of cutting surface across the bit face perpendicular to each other) seem to cut faster and last longer. Cheap HF hammer bits aren't worth the hassle in my experience.

    Regular masonry / concrete bits go through the basalt rocks in my local quite easily.

    I hope you aren't thinking of using a regular hand drill that claims to be a "hammer drill". Rent a SDS Max hammer drill and it will take care of the job quite easily and save you a lot of effort. I picked up an old Bosch spline drive hammer drill from a second hand store for $40. It lasted about 5 minutes before it refused to drill no more. I put in a pair of new motor brushes and have gotten more use out of it than I had ever imagined I would. Cleaving the face off a rock with several holes drilled in it it has been quite easy for me (like I said previously; local basalt rocks) By the time you get to the 4th hole the chunk will usually fall off by itself. You will probably discover pretty quickly that you will need to start drilling perpendicular to the surface of the rock. Once you have a pocket formed you can rotate the drill and bit to a horizontal position.

    I would be concerned about the vibrations from a hammer drill dislodging the rocks above the one you are drilling... please be careful!

    https://www.ebay.com/itm/29499777597...IAAOSwc8BigZWw
    Last edited by Michael Schuch; 05-23-2022 at 5:08 AM.

  7. #7
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    Here's a video from my favorite stone tool manufacturer on wedges and shims. I'm sure there are many youtube videos too. You can buy Chinese wedges and shims off Amazon much cheaper than Trow and Holden. I spray paint them with flourescent colors to make it easy to find them after a stone splits.

    https://www.youtube.com/watch?v=NueQ2Lx6eKo

    The stone in that foundation looks like river rocks. They drill pretty easily, so you may not even need a hammer drill.

  8. #8
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    Lots of walls are built with stones that are not flat/level, including angled as you show. If that stone is stable, leave it be. With or without reinforcement by pins, etc., when you mortar in new stones and rubble, the cement will make things strong. Working some rebar into the repair isn't a horrible idea, IMHO.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  9. #9
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    Stone masons around here work just as Jim has described. Even using wire to hold wonky rocks in place until the mortar sets. The concrete bonding adhesive painted on clean stone prior to type S mortar is very strong and very sticky. It is also rated for thick mortar joints. I have packed type S into joints up to 4 inches thick with good results.
    Best Regards, Maurice

  10. #10
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    FYI My Hilti hammer drill is rated for a 1/2" diameter hole at 18 inches a minute in hard concrete. So much faster then a home store version.. Stone will have silica so wear a dust mask. Use a hose to flush out the hole from time to time or you waste time recutting the dust. A drinking straw and a mouth full of water can be enough to get a face full of muck.
    Bill D

  11. #11
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    ...years ago Dow Chemical had a product called Sarabond and could be used to lay an 8' jackarch w/o a steel lintel for support. ifn the stones are cleaned well I would mix a gallon of bonding agent from home depot with every batch of type S and forgo all the rebar and hole drilling.

    ....opinions



    bonding agent is a polymer (Elmers glue)
    Last edited by Lawrence Duckworth; 05-23-2022 at 11:00 AM. Reason: bonding agent note

  12. #12
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    I've built a number of new stone fireplaces in houses I've sold mainly because we have an abandoned Granite quarry on our land. Since working on old houses, the goal is to match existing work, ideally so no one can tell the difference.

    Here is a link to a few pictures on my website: http://historic-house-restoration.com/Masonry.html That one was done with Lime Mortar as close as we could match the original.

    And here's a 1798 house that we need to rebuild the whole dry stacked basement walls on in the attachments below.

    If the goal is just to make that foundation last, the work is inside where it won't be seen, and it doesn't really matter what it looks like, the easiest fix would be to remove enough stones until you get to something flat, and fill in with bricks and mortar. Between that, and building it back like it was, only so it will last, there are endless possibilities.

    So much modern stonework makes me cringe. A third of the stone above should be across a head joint. Don't stack head joints high, whether dry stacked, or with mortar. When you lay any stone, the most important consideration is what it will hold above it, not that a place is found for it to sit. Those basic things are forgotten in a lot of modern stonework.
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  13. #13
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    Thank you all for the ongoing advice. It's given me a lot to think about. I have used Type N mortar so far on the little I have done, as I was advised that using Type S on old stonework could create further problems in the future, but maybe I should be using S instead. I only bought two bags of N and can save the second one for decorative above ground stonework later on if S is the right way to go.

  14. #14
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    Zacharys project looks like what we call rubble stack. It is indeed a method that makes Traditional Stone Masons cringe. A lot of residential foundations are surprisingly minimal. In January I did an "abandon in place" repair of a crumbling old wall that had no footing whatsoever. I made this Video so the owners could see what I did.

    Last edited by Maurice Mcmurry; 05-24-2022 at 7:19 AM.
    Best Regards, Maurice

  15. #15
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    Type N will be plenty strong enough for that wall. Even with mortar, it should be laid so that any stone would stay in place if no mortar was there. If that wall had been laid correctly to start with, drilling that hole through it would not have compromised it.

    None of the old houses here have any kind of footings. Even 43 foot tall chimneys are built right on top of the ground. The form in the pictures in the link I posted was so we could pour a footing.
    Last edited by Tom M King; 05-23-2022 at 2:09 PM.

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