Bathroom floor - Do I need to seal?

[pushkins]

There are "glue removers" but again these are chemical based and sometimes they can be nasty. They are available at most big box stores.

If you have an angle grinder you could always get a wire wheel and brush them away with the wire wheel. A small old chisel always works well.

I often use the wire wheel just because I like to get a "scour" on the floor especially if it's been previously covered with a glue, it helps with the thinset bonding.

There is no real panic on removing "all" the glue, but you must remove most of it.

[mjdonovan]

You don't have to seal around the toilet. Just make sure you use an appropriate size wax ring when you re-install the toilet. Make sure you push down hard on the toilet bowl so that you create a good seal. Then tighen the flange bolts snuggly, but do not overtighten.

[SlowCoder]

Ok, I think you guys can tell I'm trying to do this the right way. I don't want to have to come back to it in a couple of years because I half-arsed it the first time.

From answers I've gotten from you guys, it sounds like I need to properly clean the floor using a glue remover, and I can lay the tile directly on the floor using thinset. A guy at Lowes told me the correct method is to glue 1/4" backerboard, or at least some felt paper, on the floor, then my tiles on top. This would protect against expansion cracks in my grout. Another guy agreed, but said that's only true for houses that are less than 5 years old, and has to do with the foundation settling.

What are your feelings on this?

[pushkins]

The second guy is correct. If you are trying to adhere ceramic tiles directly to concrete then you need nothing else other than the thinset. (unless the concrete is green, which in your case isn't the situation).
On large areas of ceramic tile on concrete floors then yes it is prudent to use expansion joints every 30' or so. You can often see these in shopping malls they mostly use brass and laid in with the tile.

You absolutely cannot glue felt paper down to the concrete with thinset then glue down your tiles to the felt.
The use of backerboard on the floor is to stabilize the subfloor and allow expansion differences between wood and tile, useing it on a concrete floor would be a double waste of money.