you dont need wonderboard (or any backerboard) you said you have a cement slab, all you need to do is fill the cracks and lay the tile,an anti-crack treatment,like"red guard" would also be a good idea.....good luck

Ok Thanks. Everytime that I've pulled up carpet I have seen tac boards so I thought that I needed to "nail" tac boards back down thats one reason that I thought of a sub-floor. Another reason is because when I lay the ceramic I'm afraid that the basement floor might eventually crack and the floor movement will shift the ceramic tile.
Also I was thinking about using padding underneath the carpet for softness.

[This message has been edited by torint (edited January 10, 2004).]

you can nail "concrete" tac-strip directly to your slab floor,use an 8lb 7/16" pad under your carpet....before you put the tile down ,you should put an anti-crack layer,"red guard"available from home depot is a good one.but most places that sell tile will have something for this,,,,good luck