how to repair holes left by expanding anchor bolts in concrete

Question

I have a large workbench which I inherited with my current home, and I'd like to replace it with one I'm currently building, mainly since the current one is pretty small, and the top of the bench has a massive crack, so it wouldn't be safe to bolt down my heavier tools to it.

I've removed the bench, but there are four large floor expanding anchor bolts stuck in the concrete, and they won't budge. What is the best way to deal with them?

I've read some blog entries on other sites recommending I just pound them down into the hole if there is extra space (there is), and just patch it with some quick-set cement. My concern with this is:

1. There will be gaps between the hole radius and the anchor, and if water gets in there, floor damage in the future.
2. The anchor is still there, and I just cover it up, I don't want someone else in the future (new owner if I sell, contractor, etc) drilling straight down into it and facing a potential injury from hitting the anchor.

I could chisel around them and patch up a much larger, cone shaped hole I'd be creating, but I'm trying to see if there are better alternatives.

Answer 1

This is a pet peeve of mine, I use lag shields and anchors for this kind of thing because those expansion bolts are such a pain if you want to move things, and eventually you move everything.

I see you got the big-hammer solution, people love giving that advice. ("Just pound it in! BFH (big hammer) solves everything! What could possibly go wrong?") I'd be worried what that's doing to the concrete, and if you miss, you're going to mess up your floor.

First thing to try: loosen the nut and put a prybar under there, or a claw hammer, whatever, and see if it pulls out. Sometimes if the hole is overdrilled and / or the concrete isn't that hard, they are easier than you'd think to pull out.

At the risk of giving a big-hammer solution, if you whack the nut horizontally in all directions, regular sized hammer is adequate, it may crumble the concrete enough that the thing pulls out with a claw hammer or prybar.

Another one that might work: tighten the nut with a wrench until something gives. Of course you'll need something sturdy that won't spin between the nut and the floor. The bench's hold-down bracket may work. If it snaps off it will probably snap off well below the surface, epoxy it and forget it ever happened.

I normally just cut them off flush with a hacksaw, but there are other ways to go ... same ideas as in this answer.

I wouldn't worry about the next person; it's going to be very visible there's something there, and people always need to be cognizant they may hit metal when drilling in concrete.

You could drill around it with a core bit and snap off a core that would just lift out, but that's way way more trouble than I'd go to unless you happen to have a core drill and a small bit lying around.

EDIT: I thought of one other thing. You could get a hammer drill and a bit a little bigger than the bolt, and drill down right next to it. That will weaken it's hold enough that you can get it out with a little persuasion. Then you can fill the hole with the epoxy. A hammer drill and bit that size is much easier to get a hold of than a core drill.

Answer 2

just smash it into the slab with a hammer or cut it off with a cutting wheel on a grinder. its a tool room. if you worried about water (don't know why as concrete is porous already, and unless you are planning an indoor pool, this is no concern of any import), just smash it in subgrade and then pour epoxy or polyester resin over the hole. its thin enough it will wick in everywhere and if you use a thin enough resin, it will essentially self level. Just A Work Room.