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I have drywall in my bathroom that has started to flake and has become damaged over a few decades of use over a shower that didn't have an extractor fan.

I'm currently in the process of planning out the new extractor fan project, but I'm not sure what to do about the drywall. Here is a picture of the situation:

Bathroom Drywall

I've seen videos of drywall failure modes similar to this, and their solution was to use a 6" putty knife to scrape off the hanging drywall until the remainder was totally flat and then coat it with 20-minute joint compound.

I'm not entirely certain if that would work here because (As others pointed out in similar questions) joint compound is water soluble.

What is the best solution to this problem, and what tools would I need to implement it? (I'm kind of new to drywall, although I do have a 6"/12" steel putty knifes and a mud pan)

NOTE: I think that this differs from (repair drywall in the shower) as my drywall is not water damaged in the same way, and thus likely won't have the same answer (To the best of my knowledge), and is also different from (How do I repair drywall around a bathtub?) due to not being crumbly and other types of damage to the drywall being done.

  • Hot mud or 20 minute mud holds up much better to moisture than topping muddy or standard joint compound once sanded and a good coat of paint it will look better, use caution with hot mud and don't put it on two thick because it is much tougher to sand. – Ed Beal Dec 16 '18 at 20:55
  • Isn't 20-minute mud standard joint compound that dries in 20 minutes? – Sarah Szabo Dec 16 '18 at 21:01
  • No 20 minute mud or hot mud is not standard joint mud that takes 8+ hours to dry in most cases unless very thin. – Ed Beal Dec 16 '18 at 23:14
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    Setting-type (dry mix) joint compound is indeed tougher than standard joint compound. However, the 20-minute variety is not for the uninitiated. It begins to set very quickly and can leave a person with a really nasty mess. Use 90-minute instead, which is plenty fast unless the house is burning down and you need the job done before you escape. – isherwood Dec 16 '18 at 23:48
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To my mind the solution isn't dependent on your choice of joint compound (though topping compounds lack the vinyl component which can help with bonding). Even if you use concrete to coat it, what's behind it is still susceptible to water damage. Instead, moisture management and a good primer/paint coating is important. Your walls simply shouldn't be exposed to prolonged moisture.

I'd scrape away all loose material and finish the surface with whatever mud suits your fancy. Prime it with something that seals well, and use a high-quality topcoat that claims to bond well and protect against moisture damage.

An exhaust fan should be on a modern digital timer. Run it for at least two hours after a shower, as the moisture stuck to the tub and your towels takes a while to evaporate.

  • Great idea for using the 2-hour digital timer. I tend to take longer showers, so 2 hours is a lot better than 1 hour for drying the towels. Would homedepot.com/p/… be a good primer for applying the mud to, or is this a sealer? – Sarah Szabo Dec 17 '18 at 0:04
  • Doesn't really matter how long your shower is. It's not so much the vapor in the air as that left on the tub wall and in your towel. If the fan is running during your shower, not much should accumulate on the paint anyway. – isherwood Dec 17 '18 at 0:12
  • I won't be doing any product endorsements. Sorry. Speak to the sales rep and read the label. It usually won't steer you wrong. – isherwood Dec 17 '18 at 0:13
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If you're super-keen, you could rip all the drywall out and replace it with greenboard (regular drywall with a water-resistant facing). It may not be necessary in this case, but I believe it's the ideal solution if you have an unlimited budget and schedule. And it would give you plenty of practice with handling drywall!

I don't believe you really should go to such lengths in this instance, but I'm mentioning it for the sake of completeness.

  • Yeah, I agree and don't think that's necessary, but great answer! I didn't even know about greenboard. – Sarah Szabo Dec 17 '18 at 9:14

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