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Unread 05-08-2012, 01:43 PM   #1
Join Date: Jul 2011
Location: Canada
Posts: 5
Green board? Cement board? Kerdi board?

Hi Everyone,

My friend and I are going to attempt to update his old shower with new tile.
Right now everything is ripped out down to the studs.

What should go on the walls? green board? cement board? Kerdi board? Cement board with Kerdi over it? Green board with Kerdi over it? Or Green board with Redguard (or similar product) Cement board with red guard?

So many options, I don't know what is acceptable, recommended, or preferred out of any of the above?

According to the Kerdi book, you can install it right over drywall... That seems stupid to me, but what are the other options?

Thanks for any help.
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Unread 05-08-2012, 01:49 PM   #2
Join Date: Jan 2008
Location: Grand Rapids, MI
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You're going to get a mixed back of answers here.. so I'll start by throwing mine out there first.

I PERSONALLY prefer a traditional shower installation. Traditional in the aspect of, PVC/CPE pan liner installed properly and cement board with a proper vapor barrier behind it. When properly installed it will last decades. And then some more decades. Personally, I don't trust anything else. Just my own take.

Now sit back and wait for all the other opinions.
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Unread 05-08-2012, 01:53 PM   #3
Join Date: Jul 2011
Location: Canada
Posts: 5

I forgot to mention that the bottom is a tub, but there is also a shower head so the walls obviously need waterproofing.

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Unread 05-08-2012, 01:59 PM   #4
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Depends on your budget and what you prefer to work with. I went concrete board with Kerdi on my shower, it's overkill...but that's my life!
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Unread 05-08-2012, 02:15 PM   #5
Join Date: Jul 2011
Location: Canada
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I guess if I don't NEED cement board, then why not just use green board, with a red guard layer over that?

Is that acceptable in the tile world?
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Unread 05-08-2012, 04:49 PM   #6
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Join Date: Jul 2004
Location: Nashua, NH
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Green board (note, there is one board that is green that is not 'greenboard') has fallen from favor and is no longer allowed by code in a wet area...it is designed as moisture resistant, and that was a stretch - it never really worked well.

On a tub surround with a shower, you definately don't want to use anything with paper or gypsum in it (the exception being Kerdi, but you must follow the instructions carefully and to the letter!). Any of the approved materials can be used over cbu if you choose to use them, or just install a moisture barrier behind the cbu and tile to it. Lots of discussions here and in the 'Liberry'.

There is some advantage to a surface waterproofing scheme - less to get wet. A properly constructed shower is waterproof without the decorative tile layer installed.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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Unread 03-21-2014, 09:05 AM   #7
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Location: Van Nuys - work valley around Sherman Oaks / up to Mulholland / down into Beverly Hills
Posts: 9
tub/shower Kerdi

replaced a tub on second floor that gave hell to the house downstairs/ window in wall was wood, now vinyl/ new tub Acrylic (economy project)/ green board on walls that flags out into room / Kerdi on tub/shower walls / Kerdi-fix caulk at kerdi to window connection and kerdi to tub / schluter seals at tub copper spout stub/ seal around valve and shower head
way too simple and I will never worry about this installation
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Unread 03-21-2014, 11:44 AM   #8
HooKooDoo Ku
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Location: Birmingham, AL
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I believe that the RedGard is NOT approved for use directly on drywall (green board or otherwise). So if you want to use RedGard (a good option, one I like over plastic behind CBU) you'll need to install CBU to apply the RedGard to.

You can still use drywall if you use the Kerdi system. Basically, it is a waterproof material with hairs on both sides. The hairs give the mortar something to hold onto. So you attach Kerdi to drywall with thinset, then tile to Kerdi with thinset, and water is unable to penetrate the Kerdi membrane. So your drywall stays dry.

As others have stated, green board has fallen out of favor. People wrongly used it in showers, thinking the green board surface was waterproof. It is not, and the water would get thru the tile and grout and into the drywall eventually destroying the drywall. The lesson here is that people were using incorrectly in showers.

The other issue with green board is that if it is used on a ceiling, something about moisture can get trapped behind the water resistant paper. Gravity with then hold it against the paper and never going anywhere. Once again, the drywall behind the green paper gets wet over time and the drywall fails.

Because of the two items above, modern building codes usually do not allow green board in showers or on ceilings.

That leaves the only place you can use green board is in "dry" areas of your bathroom. While that can be done, most people seem to say that it's use is unnecessary as a good layer of paint with protect these "dry" walls just find.

So that pretty much leaves you with three choices:

#1. CBU walls with a waterproof material behind it (plastic sheets or other waterproof material).

#2. CBU walls with a surface-applied waterproof membrane (such as RedGard)

#3. Drywall walls with Kerdi waterproof membrane.

You could argue that a 4th option would be Kerdi over CBU, but most consider that overkill.

Of the three systems listed above, the higher the number, the better the waterproofing is generally considered (assuming it has been installed correctly). But the higher the number, the higher the cost as well.

As a DIYer, I consider option #2 to be a minimum. One of the pluses is that the CBU will never get wet, and therefore it is said your shower will dry faster.
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