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My garage floor is probably 50 years old and is severely pitted, and decidedly not level. I don't mind it being un-level, but it's so not smooth that sweeping is much harder than it should be. Can I put a thin layer of self-leveling concrete on it to just smooth it out, or would it all pool in the lowest spots? I'm open to other ideas on how to get it smoother as well.

  • Skim coating the concrete may not work if the surface slab is in rough shape. If it is severely cracked and heaved, you may need to replace the entire slab. – Jason Hutchinson Nov 12 '15 at 21:22
  • it's rough all right, but there are only a few cracks. If replacing the entire thing is my only option then I'll most likely just do nothing. – DrewJordan Nov 12 '15 at 21:38
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Why bother with self-leveling cement? Just use regular cement and a long straightedge to make it flat. Note that most of the smoothness of regular cement mix comes from working it with a "cement float" to work out the bubbles and help bring the "cream" to the surface.

  • How thin is OK for regular concrete? I would be OK with this approach but I don't want to add several inches to the entire floor if I can help it... I'd rather stay pretty close to the highest spot and I can add to the lower spots if need be. – DrewJordan Nov 12 '15 at 21:37
  • @DrewJordan: Mortar mixes can be spread as thinly as 2 mm (3/32 inch). See this. Mortar is mostly cement mix and if it has no gravel, it can be worked pretty thin if it is (a little) wetter than recommended. – wallyk Nov 12 '15 at 21:44
  • But wallyk, this is a garage floor probably with vehicles. You don't want to be skim coating with cement. – ojait Nov 13 '15 at 1:08
  • @ojait: I didn't mean to suggest it should all be skim coated. Just that it could with a solid surface on it (like tile). Presumably the roughness to smooth out would require much more than a skim coat. But, point taken: The thicker the better, but certainly it won't need 4 inches of thickness. Perhaps 3/4 inch would do? – wallyk Nov 13 '15 at 1:27
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    @DMoore: Crumbling occurs from flexing whether by weight loading or freezing, etc. In this case, the concrete underneath should provide plenty of rigid support to prevent flexing. If the underlying slab is broken so that it teeters as weight moves around, then sure, the "topcoast" will crack at the seams. But a topcoat which conforms perfectly to the slab should not have any movement relative to it and so can't crumble. – wallyk Nov 13 '15 at 3:20
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If the slab is a matrix of cracks and divots it may be best to take a weekend to repair the damaged section. Depending on the size to be repaired and the extent of the damage pouring fresh concrete into an excavated slab will ensure you never have to repair it again. Here's how: Chalk the outline of what area on the slab is to be repaired (go back to sound undamaged concrete). With an abrasive blade for concrete in a circular saw plunge cut the blade into the chalk line (have several blades on hand). Cutting depth should be 1 1/2 - 2 inches. With a heavy sledge start in the middle breaking out the concrete. Stop and remove chunks occasionally. When you approach the cut line switch to a smaller sledge and cold chisel. *****Should I continue?*******

  • Uh, no, thanks... This is definitely good advice, but I'm trying to avoid breaking it up and pouring again, which is why I mentioned the self-leveling stuff: I'm looking for m=something to make the top smooth, I don't really care it it's actually level or not. – DrewJordan Nov 13 '15 at 11:42
  • Not the nicest thing to do on a weekend, I agree. You can float it smooth with a cement slurry (as been mentioned) and it will look beautiful, too. The problems start shortly after when vehicles are driven on it and it will look like it does now. The concrete needs thickness to maintain its' composition. – ojait Nov 14 '15 at 1:19
  • I hear ya. Its a workshop garage though, no vehicles go in there. I guess if I have problems with the top coat I'll end up doing this anyhow, but I'm going to try the easy first. Worst case I'll have some more loose stuff to break up. – DrewJordan Nov 14 '15 at 1:23
  • No your good to go. I was assuming that it was a vehicle-type garage. This changes the whole scenario! wallyk has the correct answer about using a slurry to float it smooth. DMoore also had a good suggestion about using an admixture or primer for concrete for a stronger bond to the old floor. Also, they are selling a floor patch with fiberglass strands which is supposed to increase it's strength immensely. – ojait Nov 14 '15 at 1:31

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