Navigation

soft top layer of concrete

by Ken
(Niceville, FL)

Q. Just recently (3-weeks ago)had a slab poured for a 300sf addition. Just noticed that the top layer is soft and comes off easily. Basically, you can sweep the top layer off with a broom. I'm pretty sure this was caused by over-troweling during finishing. My concrete guy placed the concrete one afternoon and then came back the next morning to power trowel because it was a little bit cool (not freezing) that evening and it wasn't drying quick enough to finish that night. The next morning he "sprinkled" water on the top and power troweled it. while doing so he worked up a pretty good lather and I think this is what's now coming loose. Does this sound like a good theory and what's the best fix? I'm assuming he'll need to mechanically remove the top layer and replace with some sort of toping/leveler? Any suggestions? Wood floor will be glued down as finish floor.

A. You're exactly right. That cream that he created is coming off. That's what happens when you overwet the surface to aid in finishing. The concrete is still structurally sound so it's not that big a deal, especially since you're going to cover. I recommend a polymer topping to get the floor back to a semi-smooth finish. Just trowel on a rough grade overlay material and it will be fine.