CBU vs Greenboard in bathrooms [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-05-2001, 09:52 PM
Hello to all,

I first want to thank all of the forum participants for their advice. The site has been a wealth of information.

I was recently in a home where there was a separate "pool bath". This area had a shower, toliet, sink....the usual.

The walls were all greenboard but there had been evidence of the room being flooded. My guess is the toliet backed up.

In any case, the greenboard was trashed from the water. Could CBUs be used on the walls ( non-tiled), then painted, textured, etc?

I was considering using 1/2" Hardibacker down low, then match it with the greenboard about 3 feet up.

Pls advise....


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Bud Cline
08-05-2001, 10:18 PM

Beauty is in the eye of the beholder you know. How would you treat the joints of the CBU. To tape them with thinset, which is the norm, would certainly be telltale. What would you texture with? I have, (ok everyone plug your ears this is for Jason only) I have blown thinset thru a texture gun/hopper to dress some edges of broken concrete on a stacked retaining wall. Do you know what Gunite is and how it is applied? Basically the same thing only the poor mans version. This worked pretty good actually but was slow going. I don't suppose thinset is designed to be slung, but I did.

Then theres the paint or final finish, but Sonnie can come up with a workable solution in that area I'm sure.

Jason, do you expect a repeat of the flood or what?

So to answer your original question I would say "certainly", provided everyone is aware of the appearance of the end look. Using a cement based texture may just do the trick though.

Rob Z
08-06-2001, 05:51 AM
Hi Jason

Cement board can be finished just like drywall and with products like US Gypsum's EZ Sand or USG's Durabond. Go to USG's website and read about it. You could put up the cement board in the affected area and skim the surface with EZ Sand. Sand, and then paint.


John Bridge
08-06-2001, 06:00 AM
Shootin' thin set through a hopper, huh? I'm tellin' Dave G., and you're gonna get busted, fella.

On second thought, maybe I'll just tell Art.

08-06-2001, 06:09 AM
Gunite Huh....

Never thought about that....

Considering the location of this room, the number of kids that use it during the summer, and the kinds of things kids try to put down toilets......YES, I AM EXPECTING ANOTHER FLOOD.

I'll try the USG products for surfacing. Will the EZ-sand also work for the joints? I'll check out the website.


Rob Z
08-06-2001, 06:12 AM

EZ Sand is a product that can be used completely as a substitute for the ready mix mud in the bucket. It comes with numbers on the bag...5,20,45,90, 120 etc. These indicate relative drying times, affected by temperature.

Inspite of its name, it's not as easy to sand as regular drywall mud.

Bud Cline
08-06-2001, 07:18 AM
Why would you go to the trouble and expense to do this with CBU's then use gypsum products (Durabond/EZ Sand) to finish the walls. The gypsum products are the major problem now.

If it happens again you won't lose the CBU's obviously but the joints, skimcoat and finish will explode into never never land once again.

John Bridge
08-06-2001, 03:07 PM
Well, I'll see if I can put a fly in the ointment. The reason they pull the lower sheetrock off the walls after a flood is not only because the sheetrock got wet -- it would dry out. It's because of the smell and the mold inside the wall that you can't get rid of otherwise. The water will still get inside the wall using backer board. ;)

Bud Cline
08-06-2001, 03:22 PM
I don't know about there John but in the north there are companies (water restoration) that can treat all that, inside the walls and out. Insurance companies love these guys.

Seems to work OK.

Rob Z
08-06-2001, 05:26 PM
We're not talking about 2 feet of water in here. A toilet overflowing might put an inch of water on the floor. Hold whatever is on the walls up an inch or so, with the gap below covered by base.

08-06-2001, 05:27 PM
Hi Guys,

Thanks for the suggestions.

Based on the info so far, It seems the best remedy is to stick with the greenboard but leave it off the floor several inches to prevent wicking. Creative baseboard work can offset the difference.

Would applying a waterproofing agent to the sides and edges help in this case? If so, what product would you recommend?
Remember this will eventually be painted / textured

Whada ya think??????????????


Bud Cline
08-06-2001, 06:10 PM
I'd be tempted to run 3-1/2" of cement board at the bottom of the wall, silicon it at the floor, then install 4" vinyl cove base with silicon (except the out corners hot glue will be needed)and wa-la done. Semi water resistant, nothing can be damaged by just a couple inches of water, nothing will have to be replaced when it happens again. Silicon all junctures and seams to keep water away from studs (temporarily).