I am finished out my summer porch into a 4 season porch, and I am tiling the floor because we have a lot of left over tile from our entry way remodeling. We have 16'x16' porch with 1-inch pine deck floors. underneath is 2x10 supports that will house 12" of matted insulation. The idea that I came up with about what to space the tile from the pine floors is either 1/4" High-density plywood, or 3/4" plywood. Any suggestions for this project? Thanks!!

You don't state the size of tile you will be using, but to do the job the right way, lay at least 5/8" (3/4" is even better) good quality plywood, (with no voids between the plys) and screw to the pine with sheetrock or deck screws in a 8" grid pattern. Leave 1/8" space between the sheets of plywood for expansion. Stagger the plywood like bricks so four corners never meet at one point. Then lay 1/2" Hardibacker brand or similar cement board over the sheetrock set into a base of thinset mortar (3/8" teeth ok). Again, bridge the plywood with the cement backerboard, and never have 4 corners meet at one point. Screw the backerboard down to the plywood with Hardibacker or similar cementboard screws, in a 8" grid pattern. Use fiberglass tape (made for mortar)and thinset mortar to join the sheets together. Let dry, and now you are ready to set the tiles into a thinset mortar mix on the cement boards. Use an acrylic admix to strenghten the grout. If done this way, the floor will last a lifetime.