Can fiber cement board be used in a ceiling?

Question

My bedroom ceiling is water-damaged from my upstairs neighbor's leaky AC unit. I want to replace the ceiling drywall with fiber cement board. My contractor says I should instead use "water proof drywall" because FCB is only used in bathrooms. Is there any truth to this? Would there be any long term problems with replacing ceiling drywall with FCB? Is water-proof drywall even a thing?

Answer 1

Yes you can use cement board on ceilings. Is it a good idea?? Not sure.

Things to think about...

• The water won't saturate cement board. It will sit on it. So is there a small amount that will evaporate? Or is it too much and will it sit and then travel to other parts of your ceiling which makes this a bigger issue.

• Cement board is thinner than drywall. So you will have to skim coat mud until it meets with other drywall (you have to skim coat it anyways so the paint texture matches). I am guessing you wouldn't do the entire room. Again I don't see an issue doing a whole room but wow skim coating a big ceiling... lots of work.

• Drywall actually handles water really really good. I heard some test that drywall wetted with a cup of water 500 times was almost as strong afterward. I am guessing your water issue is that the water makes the paint on the drywall look bad - and is really hard to fix.

• water resistant drywall (green board) is crap. It is only a slight bit better at providing protection and is not proven to be any better than regular drywall with repeat water exposure. Green board is better at handling super moist air basically - which is why it is used in bathrooms. If you paint drywall with an oil based primer and then oil based paint it far far surpasses green board with latex as far as water future proofing.

• there is nothing to say that green board is any better than regular drywall when the water is coming from the non-face side. I have seen no studies on this and in your situation greenboard equals generic drywall.

• You could cement board your whole house if you wanted to (heavy house). I use cement board above showers sometimes (when bathroom is small or ceiling in shower is low).

• Like I mentioned before there is no waterproof drywall. If you want to waterproof it pretty good you could paint both sides with oil based primer/paint. That is a lot of work. If you wanted to truly waterproof it you could go overboard and paint at least the back with redgard.

• If it were my place I would just stick to drywall. If there is a new leak it is easy to take out a square and replace. I would rather go through replacing a square here or there than taking out an entire ceiling and putting a new one up.

Answer 2

If your goal is to protect the ceiling from leaks from above easies method would be:

Install a strong plastic foil and staple it to the beams.

Then use moisture resistant drywall (green or pink)

You can find the foil in the painting department used to cover during paint job