# 5/8" Fireboard (Paint) meets 1/2" Cement Board (Tile)



## Ininkus (Dec 28, 2008)

I've never done anything with fireboard/cement board, but I can tell you I have seen drywall finishers mud 1/8" surface differences more than a handful of times and make it look perfect.


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## Mop in Hand (Feb 5, 2009)

On point #3, corner bead will do more harm than good if there is any chance for getting it wet. As for the rest your screwed. (not really). This is what I would do. First I would tape the inside corners of the cbu with cbu tape and thinset. It's a special tape, not just the fiberglass stuff. Next, I would take a 1/4" x 1/4" square nothched trowel (doing 1 wall at a time) cover the cbu only with thinset then smooth out the notches. This should give an even coat of 1/8" over your cbu. Next tape over the flats using the same tape and thinset. A thin coat of thinset on your drywall isn't going to hurt a thing. Last, I would Redquard over the thinset with 2 coats.


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## LeviDIY (Apr 16, 2009)

Ininkus - yeah you are right, except I'm no professional 

Mop In Hand - you actually scared me for a second with the screwed comment. What you are describing makes sense.. I'm a bit concerned about getting that initial layer of thinset smoothed out well enough... but just to clarify: once I get the thinset as close to equal with the butting drywall board, tape those again (In other words, the initial tape UNDER the thinset layer, then again above it?)? ALso, not familiar with Reguard... is that available at HD/Lowes or should I try a local building supply?

Thanks both for the responses... even just the initial responses help me breathe a bit easier


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## Mop in Hand (Feb 5, 2009)

No, do not tape them twice, tape the inside corners and flats of the cbu first. After you have added the 1/8" thinset then tape where the drywall and cbu meet. Sorry about the mis-spell. It should read "Redquard", available at Home Depot or Lowes. It's a waterproofing membrane in the tile section. Use a magnesium trowel to smooth out the notches (works better than a regular float). Be sure your thinset is dry before Redquard.


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## LeviDIY (Apr 16, 2009)

OK ok... now I think I'm picturing it... get the 1/8" of thinset along the WHOLE cement board... I was thinking just at the joining of the drywall and cbu. so, thinset across the board... smooth it out... tape with redquard... 2 coats... then the regular thinset layer to lay tile on? 

Sorry to be such a pesky questioner... gotta be sure I get ya on this  And I really appreciate the advice.


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## Mop in Hand (Feb 5, 2009)

Yes, except "tape with Redguard?" Redguard is a membrane that is rolled on. (I use a foam roller) Cbu tape is also available at HD. Good Luck


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## Rory Read (Feb 9, 2010)

If you plan on covering the entire cb and only the cb with tile, could you look around for slightly thicker tile, or create a border, either with some sort of edge tile or wood or pvc trim over the 5/8 rock? 

I think I would be looking for a way to avoid building up the 1/8th difference. No matter how it's done, there is going to be a transition with a reveal. Why not build it into your design, taking advantage of it to create a cleaner and easier install?

Just a thought.

Good luck,

Rory

RDG Read Development LLC
Portland, OR


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## SubSailor (Feb 25, 2008)

I like rory's idea of an accent to hide it, (something dark) For future reference all firerock is 5/8" :thumbsup:


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## Scuba_Dave (Jan 16, 2009)

This thread is from April 2009 & was bumped by a spammer


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