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Old 02-12-2010, 03:16 PM   #1
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Hardiebacker tub surround


Hello -

As part of my bathroom remodel, we removed the old 1 pc tub/surround and have replace it with a new tub. We are going to tile the walls around the tub, but not all the way up to the ceiling (just to where the old drywall ended to cover the 1pc surround edge).

I have installed the hardiebacker boards....and now have a few questions after reading more info online

1 - Do I NEED to tape ALL seams of hardiebacker before tiling ?? Does this include corners ?? How about where it meets up with the drywall ?? What if there is a 1/2" gap between the drywall and backerboard ??

2 - I assumed the backerboards was all the waterproofing I needed.....I now think that was WAY WRONG !! I did not place any barried behind the backerboard, it is just secured right to the studs. What do I do now ?? Tape seams and put on a topical waterproofer (if they exist) ?? What is Red Guard ??

I am a novice DIY'er....and am learning ALOT as I go thanks to this site and the internet as a whole.....

Any information is GREATLY APPRECIATED

Thanks

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Old 02-12-2010, 05:01 PM   #2
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you do not need any waterproofing or membrane behind the CBU.

you do need to tape and seal all joints and at the corners with mesh tape covering with a thin coat of thinset or durabond 90 compound. Then waterproof everything with Redgard. For the top gap just fill with the thinset. Redgard is a paint of waterproofing that has your job in mind. Find it is small tubs in any tile store or the tile section of box stores. Be sure your CBU (the backer board) is at least 1/4" - 1/2" up from the tub edge or shower floor

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Old 02-12-2010, 05:17 PM   #3
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Ok.....a few more questions now

Do I tape the top gap seams between the drywall and CBU ?? What kind of tape do I get ?? Different from drywall mesh tape I assume ??

My installation directions for my tub told me 1/8 gap between CBU and tub rim...so that is what the installation is currently set to.....do I need to change this ?? Oh YUCK...... :-(

Thanks again
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Old 02-12-2010, 09:51 PM   #4
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Tape ALL seams. CBU tape is available (mesh) at hardware stores. (I don't see the difference between CBU tape and regular drywall mesh tape other than the color, but there could be) I have used both. Thinset the 1/8th inch and flat tape it. Cover it all with Redgard.
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Old 02-12-2010, 11:57 PM   #5
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Quote:
1 - Do I NEED to tape ALL seams of hardiebacker before tiling ?? Does this include corners ?? How about where it meets up with the drywall ?? What if there is a 1/2" gap between the drywall and backerboard ??
YES tape all the seams but tape them as you install the tile to prevent humps and bumps from getting in your way.

Quote:
2 - I assumed the backerboards was all the waterproofing I needed.....I now think that was WAY WRONG !! I did not place any barried behind the backerboard, it is just secured right to the studs. What do I do now ?? Tape seams and put on a topical waterproofer (if they exist) ?? What is Red Guard ??
You are correct - you are wrong! A moisture barrier IS REQUIRED behind the Hardibacker, it's in all the rule books. All is not lost however because RedGard is a topical waterproofing product that will bail you out. Use two or three coats and you'll be fine. In this case however you would tape the seams first but don't use thinset to bed the seams. Use the RedGard over the tape.

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I am a novice DIY'er....and am learning ALOT as I go thanks to this site and the internet as a whole.....
You'll do OK, no real harm done so far.

What else???
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Old 02-13-2010, 12:06 AM   #6
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Quote:
Bob Mariani
you do not need any waterproofing or membrane behind the CBU.

you do need to tape and seal all joints and at the corners with mesh tape covering with a thin coat of thinset or durabond 90 compound.
The Rule Book says that YES you do need a vapor barrier behind cement board. TRUE, if you use a topical waterproofing it is not necessary, you don't want both.

NEVER use DuraBond 90 or any other gypsum product in a shower even if you are using a topical liquid waterproofing. Those waterproofing products are great things but they are also vapor transmissive. I won't go into how a product can be both waterproof AND vapor transmissive but they can be.

When taping and using a topical waterproofing, the tape and waterproofing is all that is necessary in my opinion but plenty of waterproofing must be used to close all the holes in the tape. If thinset is used ahead of time and allowed to dry it will cause a hump in the surface that may be difficult to work with.
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Old 02-13-2010, 09:41 AM   #7
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So if I tape as I tile, using the thinset to adhere the tape, how do i red gard the seams then ?? Wont the seams be "not waterproof" then, or does the thinset do a good enough job that it is not needed ??

Also - A contractor I spoke to said I could use drywall joint compound on all the seams and then red gard over that ?? Is this anything you have ever heard of ?? What is your opinion on this ??

Thanks again for the info
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Old 02-13-2010, 10:13 AM   #8
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Quote:
Originally Posted by shaggyb View Post
Also - A contractor I spoke to said I could use drywall joint compound on all the seams and then red gard over that ??
Quote:
Originally Posted by Bud Cline View Post
NEVER use DuraBond 90 or any other gypsum product in a shower even if you are using a topical liquid waterproofing.
Shaggy - Drywall joint compound is a gypsum product.

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Originally Posted by Bud Cline View Post
If thinset is used ahead of time and allowed to dry it will cause a hump in the surface that may be difficult to work with.
Hey Bud, I don't quite get what you're saying here. What do you mean by ahead of time?
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Old 02-13-2010, 01:28 PM   #9
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By ahead of time.....do you mean doing it before the redgard or tile installation ??

So lay it out for me in basic terms....step by step....is this right ??

Step 1 - Apply tape to ALL seams around tub [QUOTE - BUD] "In this case however you would tape the seams first but don't use thinset to bed the seams. Use the RedGard over the tape." [QUOTE - BUD]

Step 2 - Apply RedGard over ALL CBU AND SEAMS.....2 or 3 layers over the seams to fill all the holes

Step 3 - Begin tiling...using thinset as tile adhesive.....thinset goes over EVERYTHING ?!?!?

I am WAY confused now...

Last edited by shaggyb; 02-13-2010 at 01:31 PM.
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Old 02-13-2010, 03:06 PM   #10
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STARTING OVER.

The tape is sticky on one side.
The tape is stuck over the seams and in the corners.
Either thinset or RedGard can be used to bed/fill the seams.
If thinset is used, a hump develops.
If RedGard is used not so much of a hump develops.
If only RedGard is used it will take several coats to fill all the pin holes.
Using RedGard will result in less of a hump than using thinset.
The entire surface can then also be waterproofed with RedGard.
If you intend to use RedGard to waterproof the entire surface then you DO NOT want to place a moisture barrier on the studs behind the wallboard.
If you do not intend to 100% waterproof the surface with RedGard then the use of a vapor barrier on the studs behind the wallboard is mandatory.
Thinset is then used over the RedGard to apply the tile.
Thinset sticks to RedGard.
RedGard is formulated so that thinset will stick to it.
RedGard is not the only liquid applied waterproofing product that will work.
I am not partial to RedGard.
RedGard is readily available here when nothing else is.
I choose RedGard for that reason.
Other liquid applied waterproofing products that may be found in your area include but are not limited to:
Mapei HPG
Laticrete Product 9235
Laticrete Wall and Floor Waterproofing
There are others.

Sorry about the confusion.
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Old 02-16-2010, 10:25 AM   #11
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Oh the fun continues......

Seeing how THICK the RedGard is and will be when dried, I have come to a new concern.....

The CBU will be butting up to drywalll on all edges.....the existing drywall was shimmed out from the studs to meet up with the previous fibergalss tub surround. When I installed the CBU, I was forced to shim this out from the studs to line up with the drywall....this varied in depths also from 1/4" in some places to almost 3/4" in others......a real PAIN IN THE @$$ if you know what I mean.....

So my final depth was approx 1/8" shallower than the drywall, with the thought that the compressed thinset would put the tile EVEN with the face of the drywall where it will overlap on the edges and give it a nice tight fit.....

So now if I put the Redgard on the CBU, this will almost eliminate this depth difference and may even put the CBU out further than the drwall depending on how thick the RedGard gets.....

IS this OK ?? Do I need to reinstall my CBU and make a BIGGER depth difference between the CBU and the drywall edges ??

My wife says I should have HIRED this out.....I told her NO WAY...much more FUN to learn and do it my ownself....... :-)
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Old 02-16-2010, 12:22 PM   #12
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I think the common way of finishing the transition from cbu to drywall is to have your tile cover the transition. So the CBU and drywall should be at same level.

Experts is this correct?
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Old 02-16-2010, 01:51 PM   #13
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I have a 3"x13" bullnose tile to cover the transition from CBU to drywall....I just didnt want the tile to stick out away from the drywall or even worse be too far in and not lay level....

Last edited by shaggyb; 02-16-2010 at 02:14 PM.
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Old 02-16-2010, 05:28 PM   #14
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So now if I put the Redgard on the CBU, this will almost eliminate this depth difference and may even put the CBU out further than the drwall depending on how thick the RedGard gets.....
This is getting way out of hand.......

You wouldn't normally be adding no 1/8" of RedGard. You would be adding only (mils) of thickness.

Now I am going to venture waaaaay out there because I can't see what you have and can only imagine how out of control this is going to get. There is one way to do this without wrecking everything and starting over.

The board surface should be "flush" with the surrounding drywall surface. That's the first thing. You don't have that and building-out 1/8" isn't going to be easy at this juncture. The surfaces must flush-up if you don't want the bullnose to teeter.

My only suggestion is for you to use a 1/8" notched trowel to apply the RedGard. (I have done this on floors to create a thick membrane)

Do a neat job and comb the RedGard in a uniform fashion. Once the RedGard has dried, use a flat trowel and fill the low lines with more RedGard. After that, if you aren't built up enough you can do it one more time using the notched trowel to further build out the surface.

I have to tell you that is a Bud Cline method and is a little out in left field but it works. You must keep in mind that neatness counts and you have to be very particular in how you apply and spread the RedGard. No humps, no bumps, no gobs. Once the RedGard has set-hard it is very difficult to remove any buggers without damaging the surrounding RedGard area.
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Last edited by Bud Cline; 02-16-2010 at 05:32 PM.
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Old 02-16-2010, 06:34 PM   #15
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Bud....I Thank You a ton for your information

I get easily confused when I get conflicting info fro
different sources so I try to clarify. I had read that the
RedGard application would end up 40 mil thick so that really concerned me.

If it will only be a few a few mil thick than I can make it work

Thanks again for your info :-)

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