Seeking advice on how to fill cracks in shop floor

[Ned Otter]

So far, I'm leaning towards some type of epoxy solution for the narrow cracks, even though they are long and there will be some expense to that. I've contacted the folks at West System for their advice, and have ordered materials that will allow me to test in these low-ish temps.

I cleaned out the cracks with a vacuum cleaner and a very narrow drill bit, which is about 6" long. I probed the length of some parts of the crack, and I could put the entire length of the 6" drill bit in the crack without hitting anything. So this will be a very expensive epoxy repair unless you also use filler and change the consistency of the epoxy. I'm not so concerned about bonding the crack, only weight from above as I move heavy machinery. My first test would be to see if the epoxy/filler combination is thick enough to hold weight, but not fall into the gap, a consistency sort of like peanut butter. The filler will turn the epoxy an off-white, which I'm not crazy about, but could live with. You can use a dye to make it more "concrete-like", but with multiple small batches, I doubt you'd get color consistency between batches.

For the wider area that looks like it was in an earthquake (2nd photo from my original post), I removed most of the loose concrete, only to find that in fact there is a long piece of wood underneath (not sure how thick it is). The total thickness of the concrete is no more than 1/2", and thinner in some parts - you can see stones directly underneath the concrete in some of the photos I've attached. The concrete I removed didn't really match what's on either side of the wood, so I'm guessing is from an older attempt to fill that void.

@Tony Joyce - do you remember what kind of epoxy you used in your shop? I'd like to stay with clear epoxy, but would need a way to prevent it from flowing into the cracks, which look similar to yours.

Thanks again to all who responded - will report back here when I've gone further.

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[Tom M King]

I would get that wood out of there, and just fill it with concrete, slick finishing the top. The narrower gaps, I'd use type S mortar, and add some plain Portland cement to it, so the top can be slick finished. You don't have to add a lot of Portland to it, and if you add too much, it will actually be weaker-just enough so you can float some "fat" to the surface to finish-sorry I don't have a formula.

The only tools you would need would be a 2" margin trowel (for getting it out of the bucket, and in place, a hand float, and a concrete finishing trowel.

Saturate both sides of the crack until it won't take any more water, before you add your mix to the crack.

Epoxy wouldn't be bad for the small cracks, if they have a bottom, but I wouldn't use it for the big one.

[Ron Selzer]

At some point it could be same cost, more/less just to replace the floor
With new concrete. Could do it in sections or all at once.
Another option would be pressure treated sleepers with 3/4 t&g plywood subfloor.
Would definitely look at all options, even ones way out of the box before starting any repairs
Something to consider once you get a handle on what all the epoxy costs.
good luck
Ron

[Tony Joyce]

Although this is labeled as table top it is very versatile and stable for cracks.
http://www.uscomposites.com/kk121.html
You can use sand to fill the bottom of the crack then pour the epoxy on top for the last 1/2" or so of crack.
I do not do multiple pour on cracks like mine.
You can also use cement(small amounts,dry) as a filler in the epoxy to color.
I over filled my cracks and sanded with a belt sander. I know it sounds crazy, but it works well.

Tony