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My stone slab stair started rocking back and forth this spring. How can I properly fix it? Obviously it's very heavy, so lifting/moving it is a challenge. I'm in Ontario, Canada (in case it matters because the issue might have been caused by water freezing).

Here's the photo, the top stair is rocking:

enter image description here

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    Which bit is rocking? Longterm repair varies with that. A short term fix would be slamming a plastic shim into whatever gap you find when it moves. – Aloysius Defenestrate Apr 5 '17 at 18:47
  • Is there any existing mortar between the stone slabs? – Ed Beal Apr 5 '17 at 18:48
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    My other question is, how much water is coming through that downpipe? Half a roof? Only a little? Water saturation impacts soil heaving. You might consider moving the pipe away. – Aloysius Defenestrate Apr 5 '17 at 18:48
  • @AloysiusDefenestrate: Top stair is rocking back and forth (parallel to the house), about 1/16" of an inch or so. The downpipe drains away from house (via that white pipe, underground), about 10 feet away from the stairs, and down the slope, so I don't think it has any effect. – haimg Apr 5 '17 at 18:52
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    I am thinking when it froze there may have been enough space between the blocks for some dirt or small pebbles to get in causing the top to rock on the pivot point. Heavy stone like these keeps its shape and since it Did not wobble before it is probably something small between them. I would try using a flat crow bar like a wonder bar to slip between the stones and step on it to lift the top stone while spraying a water hose or compressed air to blow the debris out then remove the bar and see if that helped or moved the pivot point. – Ed Beal Apr 5 '17 at 21:42
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One approach is to pry up one of the tottering edges up slightly and inject exterior construction adhesive (some are rated for stone/masonry) a few inches in and staying well away from the outside edges. Then lower the stone and let it dry undisturbed.

When dry, this creates an adhesive wedge. Its sticking power is less important than its shape.

Obviously, if rearrangement or removal of the stone is someday needed, this makes it a bit more difficult, but not impossible.

However, if you think the problem is progressing, you need to address the underlying erosion problem before taking this step.

  • To "pry up" as with a pry bar, or did you mean something else? I'm afraid to chip the stone while wedging or prying it up... – haimg Apr 5 '17 at 19:41
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    Yes to a small pry bar. Stone is usually fairly resistant to chipping if done carefully. If it makes you nervous, you could tap in a wooden shim(s) until the gap is big enough to get the tip of your adhesive tube well into the gap. – bib Apr 5 '17 at 19:51

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