View Full Version : Cement board on ceiling inside shower
05-02-2007, 12:58 PM
I am a year-and-a-half into a project to rebuild my bathroom. Being totally new to this, I pretty much just read instructions, talked to people, and researched the web to figure out how to do things.
Here's my question: inside my shower stall, I ripped down the tiles and drywall, hung a moisture barrier, and then hung cement board on the walls and ceiling. The walls have been tiled and grouted.
Now, back to the ceiling. The beams are about 24" inches apart. Is this going to be a problem? Do I really need to rip down my newly-hung cement board?
Also, I'd rather not tile the ceiling. Any other solutions?
By the way, I started rebuilding my bathroom the same time that Comcast started building the tallest skyscraper in Philadelphia. Looks like the skyscraper will be finished first.
05-02-2007, 02:13 PM
you are asking whether it is good enough to have supports 24" apart, if I read you right.
AFAIK bathroom ceilings need supports 12" apart. You can unscrew the cement board and throw it away; then double the number of ceiling joists and screw drywall to it; then mud it; and then paint it with kitchen or bath paint. You can also mud the cement board and paint it; the seams even with fiberglass tape may telegraph through.
05-02-2007, 04:27 PM
Greenboard (which is no longer national code in wet areas) is spec'ed for 12" on a ceiling. Above a standard shower head is considered dry area, and regular drywall will work at 16", but I think you'd be pushing it for 24" on center. But, the cbu will be fine Tape the seam, though. You can cover it with drywall compound (a setting type might be better than the bucket stuff), a good primer, then paint and you should be fine.
05-03-2007, 08:37 AM
I really don't want to remove the cement board. Here's a thought: what if I affix supports, 12" apart, perpendicular to the beams, which are 24" apart? According to my thinking, the new supports will prevent the cement board from sagging. And then greenboard can be affixed to the new supports.
05-03-2007, 09:08 AM
sounds good to me.
05-03-2007, 10:48 AM
Just use regular drywall, forget the greenboard unless you already have it and the local inspector insists - it really isn't buying you much of anything. If moisture gets to the backing through the paint, you didn't do a good job of painting, and even the greenboard will have problems. Good ventilation is much more of an issue, regardless of what you use. I still think the cbu would probably be okay since you aren't going to be leaning on it, although adding cross braces is probably not a bad idea if you have access. On a wall or floor, definately not at 24" centers, though.
05-03-2007, 02:12 PM
normally i am eager to criticize greenboard, for many reasons. Here in this weird application it is a good thing to use instead of regular drywall, since it will remain rigid if you don't do a good job of painting. Given a choice between a straight ceiling or a sagging one, I'd go for a non-sagging ceiling. Greenboard has only one advantage over regular frywall, only one: it stays rigid longer when wet, instead of sagging first before it turns to mush.
Some kitchen bath paints claim to retard mold growth; that means slow down the progression, the geometric progression that mold cells multiply by, to become "colonies". So if steam moisture and humidity get into that paper facing on the gypsym product, which it will, you'll be fighting a rearguard action against mold. You won't see it for a long time even when it is present under the paint. But you can smell it as a musty odor, and if you chip off a bit of paint you'll smell it stronger there. That'll be years from now. Now you know why I don't like either regular drywall or greenboard. The latter is a rigid sponge encouraging mold to grow in it. The former is a soggy sponge...
The idea of adding new supports under the CBU to support it and the next layer of whatever you put, this is the interesting new idea that you had, that will work, and that I like.
05-03-2007, 06:32 PM
Rob, it seems to me the original objective was to tile the ceiling, and if that's the case you can remove the cement board and install regular drywall instead. You will have to add nailers between the ones that are there, but that's easy. No matter what you do, I would remove the cement board. :
05-04-2007, 07:24 AM
Thank you to everyone for all of your advice.
Right now, on the ceiling of the shower stall, the cement board is affixed to beams, which are 24" inches apart. The cement board is also taped and thinset has been applied. The walls are already tiled and grouted. To that end, I really don't want to remove the cement board on the ceiling. (Good thing I found this forum, or I just would've been living like that.)
So, if it sounds reasonable to everyone, I think I'll add perpendicular cross-beams under the cement board, 12" apart. This will support the cement board, prevent it from falling. And then I'll affix greenboard to the newly-installed cross-beams. After that, I'll paint the hell out of the greenboard.
I've never painted greenboard before. What should I use?
rob / total novice
05-06-2007, 07:31 PM
Like I said before, just use regular drywall over the cbu, and us a good primer and paint...you should be fine. The reinforcement is very good insurance. Not sure if the covering on greenboard can be treated the same as normal drywall...the best place to get that would be from the manufacturer. Check their website if you decide to use it instead. Greenboard is not as stiff as drywall, thus the need for shorter nailing spacing.
05-07-2007, 07:29 AM
i've never ever heard that regular is better than greenboard for any reason. Personally I have worked with both, and I haven't found either one to be stiffer or bendier than the other. I think the 12" spacing is because it's a humid environment.
i have heard from someone who worked in a drywall factory that the only difference was the additive in the gypsum that made it stay hard longer when soaked, instead of turning to mush. The big criticism over the years is that greenboard was often referred to as if it were somehow great stuff, but it isn't any better than regular. It's basically the same stuff. There were never any printed claims about greenboard, but a lot of people thought it was practically waterproof. It only "resists" falling apart if it absorbs a lot of water. That is all. It's nothgin special.
Rob, this means the way you finish it is the same for both. Mud and paint. They both have the same paper facing. You definitely can use regular drywall too. I'm not against it. Rob, since you have mentioned greenboard, I agree with that too. The two products are so close it's not funny.
05-15-2007, 07:11 AM
Can someone please advise me on the primer and paint that should be used on the greenboard on the ceiling of this shower stall?
05-15-2007, 09:03 AM
Any raw drywall should be painted with the PVA primer specially formulated for that application. Two coats of primer, then one or two coats of best quality gloss latex enamel.
Back to the cement board....it seems the reason not to put it on the ceiling is the weight....you probably don't have enough screws in it to properly support that weight.
05-15-2007, 10:37 AM
The moisture resistant paper covering of greenboard is not as strong as that on normal drywall. Also, both of them have a grain, similar to plywood (caused by the paper) that make it stronger along the long axis than the short one, so ideally, it should be installed like plywood with the long side across the supports.
24" o.c. is almost a de facto measurement for ceilings, (if there is a second floor above them then it bcomes 16", but never 12"), and I have never seen anyone insert stringers or other supports between them.