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Duppy · Feb 21, 2007, 10:07 AM

What do you use for the joint where Cement board ends and Green board starts? Thinset still?

Tile is only going halfway up the green board wall. Thinset would make sense on the lower tiled half. What about the upper?

dclynch · Feb 21, 2007, 11:09 AM

As long as the tile is covering it, use thinset and alkali resistant fiberglass tape.

Duppy · Feb 21, 2007, 12:13 PM

And what about the top half where tile is not going to cover?

dclynch · Feb 21, 2007, 12:56 PM

Joint compound!

Duppy · Feb 21, 2007, 01:09 PM

Thanks! Is the fiberglass tape harder to mudd a butt joint with than regular tape?

dclynch · Feb 21, 2007, 01:12 PM

No, but the thinset is harder to keep flat. Try to have a minimal "speed bump" and feather the thinset out a bit. Many pros do the taping at the same time as tile setting to avoid this problem.

Jamie88 · Mar 3, 2007, 02:25 PM

I'm not sure if you are setting your tile with thinset or not. Personally I would use a product called wall mastic. You can find it at the local home improvement store in 3.5 gallon buckets. I would use this product to set the tile, and some mesh joint tape to cover the joint between the durock and the green board. You can find this mesh tape at the home improvement store as well. Hope this helps

Duppy · Mar 3, 2007, 07:48 PM

Thanks. Here is a rough drawing for clarification.

The brown is where the tile is going on the back wall. The left side, where the tile is floor to ceiling, is Durock. The right side, where the tile only goes up half way, is green board.

I'm just trying to figure out how to get a smooth butt joint on the top half where the durock meets the green board and tile won't cover the seam.

I could always run the tile out past the joint a little and not worry about it. Or just use joint compound like dclynch said.

Also, Isn't Mastic water soluble? So using it in a shower is not good?

Thanks again for the replies.

nmwirez · Mar 4, 2007, 12:56 AM

Most tile mastics clean up with water but cure up waterproof. Trowel on the mastic coat to the wall over the butt seam so the top tile coarse (bullnosed) is buttered and adhered to overlap the joint by at least half the tile if its 4x4 and that will be adequate to create levelness and seal before grouting. If you are using a mortar scratch coat then you have a challenge to use a raised grout buildup over the top edge mortar base. This is a difficult method to attempt, which I have done and do not advise.