I'm installing ceramic tile in my kitchen. I am putting 1/2" hardibacker over the 3/4" plywood subfloor to start. Hardibacker recommends "latex or acrylic modified thinset" between the tile and backerboard and, "dry-set mortar" between between the subfloor and backerboard. Forgive my ignorance, but what is the difference between the thinset and dry-set mortar. Aren't they the same? Thanks for your input.