Plain drywall used as tile backer at shower enclosures

IRC 702.4.2 states that, “Gypsum board utilized as the base or or backer board for adhesive application of ceramic tile or other nonabsorbent finish material shall conform with ASTM C630 or C1178.”

Anyone know what is in those ASTM standards?

I inspected a home with 4.5 baths and moisture resistant backer board was not used at the tub/shower enclosures.

Do the ASTM standards call for moisture resistant backer in this application?

I understand what common sense dictates but I’m trying to leave common sense out of this for now.:slight_smile:

Hi to all,


ASTM C630 relates to the standard of moisture resistant drywall.

ASTM C1178 relates to fiberglass reinforced moisture resistant dry wall.

So yes, the quick answer is that the drywall should be moisture resistant.



If it’s important you can buy & immediately download the ASTM standards at . It looks like C630 has been superceded by C1396 but, in any case, all of those standards are available for about $30 ea.

Thanks guys.

i don’t use anything but M.R. board (or “green board”) for tub walls. i alway thought that the moisture in the mastic alone would be step one in the down fall of the plain drywall. never tried it, but then again you said to leave common sence out for now so…

Another reason this board is so useful. I did a search for something not directly related to this topic and come across this 9 yrs old posting that included Gerry Beaumont. May he rest in peace.

If cement board or mud set is not used…along with proper membrane application…the area will ultimately leak. Just my opinion.
Code is not the issue.

Anybody that doesn’t use, at minimum, tile backer board, is courting disaster.

Agreed, nobody uses MR board anymore behind shower/tub tile. Well, almost nobody…

Flippers might.

cement board and membrane.

Fiber-cement, fiber-mat reinforced cement, glass mat gypsum backers and fiber-reinforced gypsum backers in compliance with ASTM C 1288, C 1325, C1178 or C 1278.

ASTM C1325

This specification covers non-asbestos fiber-mat reinforced cementitious backer units manufactured to be dimensionally stable and suitable as either an unfinished substrate or as a substrate for decoration such as natural stone or tile on walls, floors, or decks in wet and dry areas.