Hello, I poured a patch two years ago in my hall to level a dip. I then laid a floating floor which worked perfect. Well, now the wife wants me to pull it up and replace it with 3/4 hickory. I have searched but have found limited information. The patch is maybe 3/8 inch at deepest point and covers area about 3 by 4 feet. Will the cleats penetrate without busting the material? Can I glue it in that area, or should I try and tear it out which will be a pain? Thanks for any help, especially from anyone who has done it.
Tim

Sure the patch will break up. Fasteners will penetrate through the patch and hold.
The problem would be if you need to remove flooring that has been laid over the patch, later. You will need to do the patch over because pulling the flooring will break the patch into lots of little pieces.
Cover the patched area with either 15 pound felt or kraft paper the keep pieces in place so none gets in between newly laid flooring.
Gluing will not be necessary since the fasteners will penetrate into the sub-floor and hold.

You could install new 3/4 in plywood over it - float method then nail to it.

Thanks Guys
Here is what I did. My sub floor, under the patch, consisted of two layers. One 5/8 plywood, and one 7/17 osb screwed together. I pried the top layer, with the patch, off. It worked well as I did not have to grind on it avoiding much dust. I then used 15 lb. felt to fill the dip, and placed a new piece of 7/17 on top which I screwed to the bottom 5/8. So the felt is sandwiched between the two which has created a smooth surface. At first I was afraid it would be spongy, but it does not seem to be. I think I will have to use extra long connectors on the hardwood directly over the thickest part of the 15 lb felt in order to penetrate the bottom 5/8 plywood. That area of the subfloor is about 1 9/16" thick. What do you think?
Tim

Asphalt saturated felt will not be spongy. 2 inch staples or cleats will hold the floor in place. Fasten your top layer to the sub-floor every 6 inches around the perimeter and every 8 inches in the field.