Q: Is it OK to use MDF moldings in a bathroom? Is the glue resistant to moisture, and what would happen if it got wet where it abuts the shower - would it swell like particleboard?
A: MDF stands for medium density fiberboard, and is a composite material made up of fine wood fibers bonded together with resin and pressed up under heat and pressure to form moldings and other items used in construction and furniture making. While MDF has no structural value, it does make a great trim material for painted applications. In normal usage, MDF is moisture resistant and is used extensively for trim and even cabinets in bathrooms. As to the second part of your question, if it gets wet and stays wet for any length of time - as opposed to just being exposed to high humidity in the bathroom - it definitely can absorb water and swell. Two things you might consider: You can find a number of common molding patterns in both MDF and solid wood, so you might want to install a solid wood piece where it butts up to the shower. Otherwise, seal the back, bottom and ends of the MDF moldings with a good primer prior to installation in any areas that might be subject to water, which will help minimize absorption.
