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Old 06-24-2009, 04:51 PM   #1
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Correct Tape where Cement Backerboard meets Greenboard?


OK, I've been searching and lurking around trying to figure this out to no avail.

We have Cement backerboard on 2 sides of the new shower stall. This cement board meets up with Greenboard gypsum on the adjacent walls & ceiling - those walls not immediately at the shower. Which of the mesh tape should we use to join the 2 different materials? Oh, and we're using regular pre-mixed joint compound for the taping steps.

Thanks !!

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Old 06-25-2009, 12:01 AM   #2
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Correct Tape where Cement Backerboard meets Greenboard?


Fiberglass mesh tape will work. Do not mud where it will get wet. Applying Reguard to your CBU is highly recommended.

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Old 06-25-2009, 09:25 AM   #3
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Correct Tape where Cement Backerboard meets Greenboard?


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Originally Posted by Mop in Hand View Post
Fiberglass mesh tape will work. Do not mud where it will get wet. Applying Reguard to your CBU is highly recommended.
Thanks for the advice MOP. We were not planning on "mudding" the Cement board - or are you referring to the Joint Compound? We will be applying ThinSet with adhesive addititive in it and apply Tile & Grout.

What is "Reguard" ??????? First I heard of this. Is this a special Joint Compound or Coat of something you apply to the entire Cement Board?
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Old 06-25-2009, 09:30 AM   #4
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Correct Tape where Cement Backerboard meets Greenboard?


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Originally Posted by cody21 View Post
Thanks for the advice MOP. We were not planning on "mudding" the Cement board - or are you referring to the Joint Compound? We will be applying ThinSet with adhesive addititive in it and apply Tile & Grout.

What is "Reguard" ??????? First I heard of this. Is this a special Joint Compound or Coat of something you apply to the entire Cement Board?
it is a waterproofing layer that you paint on.
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Old 06-25-2009, 09:41 AM   #5
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Correct Tape where Cement Backerboard meets Greenboard?


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Originally Posted by gregdonovan View Post
it is a waterproofing layer that you paint on.
hmm... OK, I see. (My head is now swimming.) My undersanding was that all we needed to do was:

(1) Plumb the wall, done.
(2) put up some water proofing sheets, done - used "Aquabar B - vapor retarder".
(3) Cut and install our cement board, tbd.
(4) mesh tape the joints, tbd.
(5) apply joint compound - which now sounds like we should be using actual thin-set with adhesive, tbd
(6) Apply thinset and Tiles and grout and seal, tbd.

So is REGUARD really needed? Will it negatively affect the thin-set for the tiling?

Thanks
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Old 06-25-2009, 10:44 AM   #6
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Correct Tape where Cement Backerboard meets Greenboard?


Is the cement board going to be in a "wet" area, or outside the shower stall itself?

If it is in a wet area then.....

Check out this thread that talks about Kerdi and Redguard.

Bathroom walls

Here is the link to the Schulter site who makes Kerdi and Ditra.

http://www.schluter.com/143.aspx
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Last edited by drtbk4ever; 06-25-2009 at 10:49 AM.
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Old 06-25-2009, 10:51 AM   #7
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Correct Tape where Cement Backerboard meets Greenboard?


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Is the cement board going to be in a "wet" area, or outside the shower stall itself?

If it is in a wet area then.....

Check out this thread that talks about Kerdi and Redguard.

Bathroom walls

Here is the link to the Schulter site who makes Kerdi and Ditra.

http://www.schluter.com/143.aspx

Yes - these are the 2 shower walls that I am referring to. I'll take a look at those links .. and I see it's called "Redguard", not "Reguard" as the other guy posted... thanks for clarifying.
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Old 06-25-2009, 12:07 PM   #8
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Correct Tape where Cement Backerboard meets Greenboard?


Since they are wet walls, my understanding is the concrete board itself isn't completely "waterproof". Therefore the use of Redguard or Kerdi.

Remmber I too am a DIY noob, so input from a more experienced DIYer will be coming shortly I am sure.
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Old 06-25-2009, 12:18 PM   #9
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Correct Tape where Cement Backerboard meets Greenboard?


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Since they are wet walls, my understanding is the concrete board itself isn't completely "waterproof". Therefore the use of Redguard or Kerdi.

Remmber I too am a DIY noob, so input from a more experienced DIYer will be coming shortly I am sure.
Yea, I feel the pain as a DIYer with all the info being pasted around. Our contractor - who did the rough-in and electrical specifically told us we ONLy needed the Cement backer board and the Aquabar B sheet between it and the studs. Then Thin set and tile and sanded grout/sealer.

I think the point is that the Aquabar B material acts as a water shield if/when water seeps thru the grout. We had considered an Epoxy grout but he convinced us to stay away from it as DIYers.. gets too messy. Sanded grout works just fine after sealing it from time to time... Thanks
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Old 06-25-2009, 08:23 PM   #10
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Correct Tape where Cement Backerboard meets Greenboard?


OK, let's see if we can put this to bed.


The Aquabar serves as a moisture barrier to keep moisture from getting into the stud cavities. Hence: aqua (water) bar (ban). The cement board is all that is required before the tile. If you wanted to spend more money on Schluter's KERDI a plastic waterproofing membrane - you could, but it isn't necessary. If you wanted to spend more money on Custom's Redgard a paint-on waterproofing membrane - you could but it also isn't necessary. Showers have been built successfully for many decades just like you are proposing.

KERDI and Redgard are state-of-the-art applications and are the best the industry has to offer for now. Use of either would be an improvement but neither is necessary.

No grout is really waterproof but epoxy grout comes closest but is a blitch to work with - stay away from it.

The seams that change from cement board to green board can be filled with thinset. If one side (outside the wet area) is to get painted, then the thinset overrun (if any) can be filled with regular gypsum joint compound and sanded to perfection for the paint.

No cement board is waterproof. They are all simply not damaged by water or moisture but they are not waterproof.

When using thinset, tile will stick to Redgard or KERDI as well as it will stick to cement board, that's what the two products are intended for.
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Old 06-25-2009, 11:24 PM   #11
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Correct Tape where Cement Backerboard meets Greenboard?


OK, REDGARD, sorry about the typo. The reason I recommened it, is because I've had one failure without it, and have not had a failure since. It was a shower remodel 10 years or so back. I used 6 mil plastic behind the cement board, taped the corners and flats with thinset and began setting tile. About a year latter, I get a call. Water had pentrated the cement board, ran down the plastic and ended up on the wood base molding outside the shower just past the door. At the time I built the shower it was being used only once daily, shortly thereafter the owner decides to rent out 3 more rooms (to pay for the shower? who knows) My best quess is that the cement board never got a chance to dry out. I've used REDGARD ever since. Granted, I'm sure that Bud has more experience with tile than I do. However, I can not afford not to use it.
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Old 06-26-2009, 08:52 AM   #12
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Correct Tape where Cement Backerboard meets Greenboard?


Got it .. And thank you Bud for the detailed explanation. I am very clear now on what we'll be doing to finish this off.

PS to MOP : no prob. on the typo ... we got it all figured out. Just wanted to mention that we'll have the Cement BB screwed in place all the way INSIDE the NOBLE polyurethene shower pan liner - to 1/4" from the bottom (so as to not wick, but yet any dampness that it might get would thus 'drain' inside the pan; not outside and down the wall.) The rubber liner actually protrudes about 6" up the walls on all sides.

Thanks again guys. Great site !
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Old 06-26-2009, 12:23 PM   #13
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Correct Tape where Cement Backerboard meets Greenboard?


Continuing:

A vapor barrier on the studs SHOULD NOT BE USED IN CONJUNCTION WITH SURFACE WATERPROOFING.

Use one or the other - NOT BOTH.

For the record...I always use cement board AND either Redgard or HPG also.

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