I'm putting tile in the kitchen and removed the old linoleum. The concrete is very smooth and I can't get thinset to stick. Can I use a acid or do I have to grind. I have tried a modified thinset and acrylpro. The acrylpro sucked and I had to pull up all the tile and clean it, that stuff did not dry after 4 days, then I tried the modified and it sticks to the tile but not the slab. We are trying to put down porcelain tile.