We just finished installing an engineered (plywood) hardwood floor. The sub floor was a combination of clay tile, tongue and grove 1 x 6 and OSB (2 additions). We were advised the warranty on the floor would not be honored unless we floated the entire floor.

I don't usually like the float application because they tend to make the floor a little springy when you walk on them. But on the OSB and T & G section the floor is very solid. The clay tile section was only 4ft x 8ft but had a slight slope and one large crack that created a bump across the 4 ft width. I used and underlayment skim coat to smooth that area and did the best I could to get it level.

However, I have a spot near the bump about 2ft wide that has a void between the floor and the tile, I would guess maybe 1/8" inch in the middle of the spot. It is in the highest traffic area of the floor so I want to fix that spot. The plan is to drill a small hole in the floor, inject something that will fill the void and then plug the hole.

I was thinking some type of epoxy that will flow into the cavity. My helper is suggesting the low expansion Great Stuff spray foam but I am afraid that could still expand too much.

Ya'll got any bright ideas?