Tile over sheetrock

[highup]

The guy I am working for is upset because he installed some waterproof sheetrock on the walls in his bathroom. The tile setter says he has to tear it out.
It's on the walls and on the wall area surrounding his large oval tub.
It's not something that will get wet, like a shower. How come they can't just install cement board over it? The tile setter says that won't work because moisture will get trapped behind the cement board.
What moisture? It's just the walls in the master bathroom and the tile will be from the floor up to about the light switch height.
The box area the tub will set on is plywood, so cement board will work over that just fine.
My question is....
Why can't the tile be installed on the wall areas and wall area surrounding the tub over the waterproof sheetrock? What are his options if it won't? Install Kerdi over the sheetrock instead of cement board?

 

[Jaz]

Hi,

Let's first of all clear the air about what you called "waterproof sheetrock".

There is NO SUCH THING!

Sheetrock/drywall is not and never was waterproof. At best it's moisture resistant, not even water resistant.

However, the tile guys is being really tough. You can install tiles over green board in a dry area such as you describe. He gets cudos for wanting to do the job the best way though.

The tile setter says that won't work because moisture will get trapped behind the cement board.

He is correct, but this is usually overlooked. He's talking about vapor, not actual water going through. Vapor can collect on the drywall behind concrete backer and cause problems as it turns back into water. This may not happen or it might take many years, but he's telling you the truth.

So, I don't think you really need the concrete backer, but should not do both. One option is to remove part of the sheetrock and replace with real half inch" concrete backer. Or go with Kerdi. Kerdi would definitely be my choice in the shower areas.

Jaz

 

[Ernesto]

Roll on water proofing like redguard.

 

[highup]

Hi,

Let's first of all clear the air about what you called "waterproof sheetrock".

There is NO SUCH THING!

Sheetrock/drywall is not and never was waterproof. At best it's moisture resistant, not even water resistant.

However, the tile guys is being really tough. You can install tiles over green board in a dry area such as you describe. He gets cudos for wanting to do the job the best way though.



He is correct, but this is usually overlooked. He's talking about vapor, not actual water going through. Vapor can collect on the drywall behind concrete backer and cause problems as it turns back into water. This may not happen or it might take many years, but he's telling you the truth.

So, I don't think you really need the concrete backer, but should not do both. One option is to remove part of the sheetrock and replace with real half inch" concrete backer. Or go with Kerdi. Kerdi would definitely be my choice in the shower areas.

Jaz

When he said waterproof, I was assuming that he had some newer kind of sheetrock or material that is waterproof.
That was my thought also on the buildup of vapor over time.
Thanks for chiming in.

Roll on water proofing like redguard.

He told me that he has a waterproofing stuff similar to that. He figured when he bought the "sheetrock" that this liquid could be rolled on and that the tile could go right over it. Or, that the backer board could be put over the sealer coated sheetrock.
He said that whatever he bought was about $100 a gallon.

 

[TEC_Installation_Systems]

You can install a vaper retarder membrane behind cement backerboard to prevent mold and mildew. Then tape the seams over the cement backerboard with alkali resistant tape. And patch the seams with skimcoat and patch.

 

[highup]

I'm slow in responding. Been a while since I left the project and the tile probably hasn't even been started yet. Homeowner is slower at making progress than I am.
That said, thanks to all responding. Info has been passed on, so no more here that we can do for him.
highup