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I have some issues with the slab that was poured for a garage, and I need to frame an interior wall over a bad area.

The slab was poured with a bit too much water (5.5 slump) on a hot day in July. I think this caused some water to get trapped, which caused a top layer of concrete, about 1/4" to 1/2" thick to peel off and sound hollow under some spots. Also, the floor isn't perfectly level, as the troweling machines were put on it too soon.

What products(*) and process should be used to correct these surface defects prior to framing walls over them?

Here are some photos:

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* By "product", I mean self-leveling, patch, hydraulic, ready-mix, etc, or a combination thereof, not necessarily a brand recommendation.

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First off you mentioned hollow underneath, was the base compacted prior to the pour, if not the whole slab is in question as the base has settled underneath the poured concrete so putting paint on a pig is a waste of money.

But to answer your question directly - clean everything you can then use "ProBond" or another Concrete bonding promoter. If you do not use a bonding promoter it has a higher chance of separating from the base.

Then use self-leveling floor resurfacer to finish the floor. If you are doing the whole floor and it is a large area you may want to consider talking to your local ready-mix company as they do provide mixes for self leveling of floors. It is used in apartment buildings and other large multi storied structures it is called "gypcrete" and may be your best best dollar for dollar. Oh, the results will be great.

  • It's not an under-slab compaction issue, if I pull off the top layer in a problem area, it's solid underneath. There's a whole lot of unlevelness throughout but it's only the couple spots where it's peeling up. So if I clean the bad spots and remove the top layer and put the bonding primer on, then how long between the bonding primer and the surface smoother? Is there a time-limit? And the bonding primer will act as a filler, or the self-leveling concrete will be the filler? – Nick Nov 29 '19 at 15:22
  • The bonding agent goes on right before the leveling mix, give it about a half hour to dry. Bonding agents only help the leveling mix adhere to the already hardened concrete they do not act as a filler. – user1946891 Nov 30 '19 at 16:20

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