Hope I got the correct area. I've solid (3/4 in) oar floor over 2 layers of 3/8 in subfloor, floated over a concrete slab, total height of 1-1/2 in. I plan on laying 712 sq-ft of stone tile at 7/16 in. I did two small rooms with a mud deck, that and the thin set, I was able to get the 1-1/2 in to match up with the wood. But mud decks arrre tough! Small romms, 30 to 40 sq-ft was tough enough, now I've got 380 sq-ft areas to lay. So I came here hoping for any ideas to overlay the slab level to make up the 1-1/16 in. I thought of backerboard, but read where it's not recommended as a floor underlayment. Any help would be much appreciated - I ain't looking forward to pounding in that much mud!