I'm just about ready to install tile over a fiberglass whirlpool tub. I've put up the durock, taped the seams with their fiberglass tape and thinset. One of the durock walls butts up to sheetrock and is a bit lower than the sheetrock. Not thinking ahead, I mudded the gap and smoothed the transition but since the durock was lower than the sheet rock the joint compound is now over the durock. Can thinset/tiles be put over the joint compound (it would be at least 3 vertical rows of tiles)? Can tile adhesive be used instead of thinset in the areas with joint compound?

Thanks!

Tile adhesive is not recommended for wet areas so stick with a modified thinset mortar, not plain thinset. Back to the durock question, by lower do you mean it is not as thick as the drywall, it is inset a bit?

Yea, the 1/2" durock isn't quite as thick as the drywall next to it. It looks like they used 5/8" drywall.

OK, I better understand your situation. No, I would not try to mount wall tiles over ordinary joint compound which will never be water proof. Scarp, chip out the joint compound and butter that joint just like you did the seams. Modified thinset will be water proof and much stronger resisting cracking. Use this same thinset to mount your tiles.

Thanks! Better to re-do it now than have tiles falling off the wall later.

Being only one wall, you might consider taking that piece of durock down and furring the wall out to be in plane with the sheetrock. Believe it or not, peel and stick tile make great shims for situations like that. Cut into 1.5" slices and stick them to the stud faces.

Is this a drop in tub being used as a shower as well? If not, and it's just a soaking tub, it's not considered a wet area and you could get away with what's there now. Though thinset is always better, if there is no shower in most cases mastic will be accetable. If it will also be used as a shower, did it have a tub flange?

It is also a shower. I think it's too late to take off the durock and raise it up, it's been taped on all other sides and its attached to the wall with a billion screws. :-) I think I will scrape off the joint compound and build it up slightly with modified thinset... fun. Thanks!

I think you will be OK. How large are your tiles and what size towel were you planning to use? A 1/4" notched trowel will raise your tiles bottom surface over 1/8".

The tiles are 6x6. I was going to use a smaller trowel but using the 1/4" sounds like it would be perfect! Thanks.