new concrete is cracking over old concrete floor

9 Replies

Working on what was an old attach garage that is now part of a kitchen. We needed to raise the concrete floor in some areas. The new concrete is now cracking and lifting form the old concrete. Any ideals as to how to fix this?

I guess I am hoping there is some way I can get around tearing the new concrete and re-pouring it. We have this wooden floor that we are planning to glue over the conrete so it will match the rest of the hardwood floors. We are just concered that the lose concrete might effect the hardwood somehow. The concrete is not crumbling. It just seems like it is no longer sticking to the old concrete. If you tap on it is sounds hallow.

Man 1/2" is not much at all. I always did a minimum of 2" thick. most likely you will have to bust it back up. I would contact a concrete pro before you do that. I have seen floors that were poured over existing concrete crack, or lift up even at 2" thick.

The problem is that there is nothing for the new crete to attach too. And because its not very thick it will be brittle.

Typically in these cases what I do is get a few wire mesh sheets (3 x 5) and nail it to the floor. If you need to you can tapcon screw it down.

Then when you trowl down your new layer the cement will adhere to the wire mesh (and create a miniture rebar reinforcement), and beacuse the mesh is fastened to the original floor you should get a good bond.

I have done this on floors that we had to mud first to level off before putting tile down.

Good luck.

I just read your second reply.... and if you dont want to tear out the concrete, perhaps you could try these:

If you are going to put down laminate flooring over top of it, then you may get away with trowling down some flooring glue, then putting 1/8" luan over it. This should stop the crete from moving around because the adhesive under the luan will hold it.

However if you are using hardwood, then you're probably going to put wood strips down where the flooring will be nailed... in this case I wouldnt worry about it. Just put the strips down with a little PL construction adhesive under them to hold the crete in place where they need to shim the flooring. Then when you put the floor in place it all will be tight as a drum anyway.