Originally Posted By: roconnor This post was automatically imported from our archived forum.
The bldg code generally permits water resistant drywall (greenboard) back-up for tiles in a shower. However I understand that cement board (“Wonderboard”) is generally recommended for this application.
Has anyone observed problems where greenboard (not standard drywall or blueboard) was used for shower tile back-up or know of any good articles that discuss this? 
-- Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong
Where the tile is installed by a good tile guy, I don't usually see problems in the first several years.
Where the tile is installed by a non-professional who really is very good at it, I see problems frequently.
Primarily due to the deterioration of the grout and the subsequent wetting of the greenboard.
It is not a question of IF the greenboard will get wet and swell, its a question of how long will it be before it does.
Concrete backerboard won't suffer like greenboard when it gets wet.
Its a question of do it cheap or do it right.
EXTRACT:
Moisture-resistant drywall, or "greenboard" as it's often called, is made out of the same gypsum core as drywall. The only difference is that it has a moisture-resistant facing.
Greenboard is sometimes used as an underlayment in wet areas such as a bathtub surround or shower. It's installed the same way as standard drywall.
Keep in mind that greenboard is not water-proof. And if your tile is not sealed properly the greenboard may deteriorate from moisture penetration.
Concrete backerboard has a solid concrete core and is faced on both sides with fiberglass. It's an ideal underlayment for wet areas like shower walls and bathtub surrounds
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Originally Posted By: roconnor This post was automatically imported from our archived forum.
The model building codes (e.g. IRC) allow greenboard, so unless there is a local restriction there is nothing an AHJ can do except point out the potential problem to designers. I think it can be agreed that cement board is a better installation, but there has to be clear documentation of a problem to even consider proposing a local restriction.
– Robert O’Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong
Originally Posted By: rking This post was automatically imported from our archived forum.
Robert,
As Erby says "Do it cheap or do it right".
The standard application up here is to use the greenboard period in the bathrooms. Some custom contractors use the concrete backboard but most do not because of the weight and difficulty cutting and screwing.
I have seen some problems with the greenboard due to moisture, I always take the palm of my hand and sort of slap the tub surrounds all the way around searching for weak or soft spots.
To date I have been lucky and I have not had any walls or tiles come falling down on me 
-- Muskoka Home Inspections
"Wisdom is the Anticipation of the Consequences"
Steering Committee Member At Large
