MDF Crown Moulding in a Bath or Shower

Installers report mixed experiences with MDF mouldings in damp areas. Climate might be a factor. March 26, 2012

I have a crown job coming up that includes two bathrooms with showers. I would like to use MDF crown because I can get it pre-primed (saves money and time for me and customer). Can I use the MDF over the showers without worry? It will be primed, caulked and painted two coats. The bathrooms have exhaust fans.

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor L:
Paints and lacquers are only water resistant, not waterproof. MDF does not do well in wet areas. If you did use it there, I would seal the back with clear and all cut ends with caulk. I would use wood myself.

From contributor B:
Actual experience - 4 years ago I put MDF crown in my bathroom. It was left over from another job. Back side wasn't painted and I didn't caulk it as suggested above. Three years ago I tore it out - it was swelling and failing like crazy - and replaced it with poplar. No issues since then. It is in a downstairs bathroom that has no fan, if this makes a difference.

From contributor R:
I have MDF in both my personal bathrooms and installed in many customer's homes. As long as water doesn't get on it or steam is significant, it should be no problem. In personal home, 10' ceilings, adequate ventilation via fan, caulked and primed both sides (factory primed), latex topcoats 2 coats semi-gloss. Looks as good as day installed.

From contributor M:
I would not want to warranty using MDF in this situation. MDF pre-primed mouldings generally are not back primed. As pointed out, the prime coat is not waterproof. Sealing the back and cut ends and 2 good topcoats may work, but having to replace the mouldings after the homeowners take a steam bath is highly likely. Waterproof/water-resistant MDF would work, but cost is much higher.

From contributor Z:
I would explain to the customer that they would be better off spending a little more for real wood in the bathrooms. Why take a chance just to save a couple of bucks? You know that you will not have problems with solid wood if installed correctly.

From Gary Katz, forum technical advisor:
We've installed miles of it, thousands of feet in bathrooms. Never had a problem. But I live in S. CA and I think the mostly dry warm climate has a lot to do with it - fans or not, bathrooms dry out quickly here. Almost everywhere else I visit in the country that is not the case, fans or not.

From contributor N:
I agree with the comments made concerning ventilation and climate... If the bathroom is accumulating moisture or is poorly ventilated, you're going to have real problems using MDF. But if you must use it, make sure you use a paint with a high acrylic content, which has a far better resistance to water than other paints.

From contributor O:
Paint will fail on wood molding if it gets wet. The proper installation and finishing is more important than what the molding is made of. Back prime and caulk or glue on all cut ends is a must.

From contributor N:
Nonsense - it depends on the type of type of paint you use. A good acrylic paint will repel water and moisture - that's a fact. Ask any paint professional.

From contributor W:
I am the owner of Pacific West Mouldings in San Diego, and I use MDF all the time in small powder rooms, over showers, etc. and have never had a callback from a homeowner. Just seal the back with paint and caulking.

From the original questioner:
Thanks for all the responses. I think I'm just going to stick with the wood crown and play it safe. I'm in South Carolina where it gets pretty humid in the summer though the air conditioning keeps the humidity down indoors. I really think the MDF would be okay because of the exhaust fans, air conditioning, and the size of the bathrooms, but I don't want to chance it.