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The Best Material for Trimwork

I’ve used MDF (medium-density fiberboard) trims and moldings for many different applications and learned from them. The small wood particles used to make MDF are pressed and glued together much like particle board, only denser and stronger.
 
I like MDF trims cause they’re sleek, easy to paint and cheap. So here’s where the rub is with MDF. I used to think MDF, once sealed with good paint would stay dimensionally stable. It comes pre-primed after all, right? Wrong! Use these trims and boards in any dry environment like bedrooms, living rooms and such but keep MDF away from bathrooms, window sills and anywhere you might have high humidity.
 
I used MDF boards milled down to fit window jamb extensions for the interior of aluminum storefront windows. Years later the condensation from the windows when the shades were closed on long winter nights has made a swelled and blistered mess. The same goes for the MDF baseboard I used in my own kids’ bathroom. Yeah, I know they take long showers and aren’t always good about getting the shower curtain closed, but still. These locations are only intermittently wet and have plenty of ventilation. No matter, the MDF can’t recover.
 
When using trims like baseboard, window casings and crown mold in wet or humid areas a better alternative is to use finger-jointed pine. The cost is comparable to MDF, and if a good primer is used, the pine will paint up nicely and be a lot more resistant to the moisture. The architect I work with most often always specs hardwood sills in commercial settings painted with oil-base paint. It kills me to take a piece of birch or maple and paint it, but his reasoning is sound. Window sills take a lot of abuse both in moisture and use. Hardwoods just hold up better. When the budget is tight and the environment is dry go ahead with the MDF. In wet areas use wood or even vinyl trims or be prepared to replace it.
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About Doug Martin

Doug Martin has always had a love for building things with wood. In high school Doug received the Outstanding Achievement Award from the Stanley Tool Corporation and then apprenticed for three years in southeast Pennsylvania, working with a custom homebuilder. Doug owns and operates a general contracting company in southeast Montana. His company, which has been in business for 15 years, contracts residential and light commercial new and remodel construction projects.

Doug has served as interim building trades instructor at Miles Community College. He enjoyed teaching students about his passion. Whether building a new dental office, remodeling a kitchen or creating a client’s home theater room dream, Doug loves working with clients to bring their visions to life.

Building in the Mountain West can be a challenge. The temperatures vary 140 degrees F, hurricane force winds occur every year, major hail damage occurs one out of ten years and rain, while infrequent, can come at an almost sideways slant. Through this experience he has learned tried-and-true practices above what a code book requires.