Installing tile over concrete (basement 225sq.ft.)

Please advise:
When laying porcelain tile over concrete floor, do you spread the THIN SET on both the tile and the floor or just the floor.

We are first time "do ityourself" installers.

You need to first make sure the floor is free from dust by using clean water and sponge.

When spreading thinset on the floor use flat side of your trowell first then use the notch side. This will give you a better bond.

And yes you need to skim the back side of tile also with flat side.

What size tile and trowell are you using?

Is the concrete sealed? The adhesive will not bond properly if it is. You can tell if it is by pouring a little bit of water on it and then rub it around a little. If it soaks in, it is not sealed or not very well. Are there any cracks in the concrete? Do you have any type of water problem?

Size of tile can be of issue but the most important is what kind of thinset and condition of subsurface and age of. Thinsets are most commonly overlooked 3 different properties to a thinset are bond strength, movement properties and body to hold up large format tiles.