Should concrete be sealed before tiling?
 

I have a concrete floor that is unsealed and would like to lay tile over it. It looks to have been poured after the walls were built or it was an old porch that was incorperated into the house. When it is wet outside, the concrete smells very musty and seems to draw moisture. I was wondering if I can seal it first and then use one of those membranes between it and the new floor?

Use Drylok masonry waterproofer

if you seal it there is a chance that the thin set won't stick very well.

+1 What DannyT said.

You have to use very specific products that are designed to have flooring installed over them. Bone Dry is probably one of the easier ones to use.