Is MDF Stable?

Cabinetmakers and woodworkers report mixed results with medium density fiberboard in terms of movement in service. December 24, 2012

I own a woodworking shop in New York City. I made some 1 3/4" doors out of MDF. They were paint grade and one reason we used MDF was because there was less possibility of warp. But the door warped after 6 months. Has anyone had a similar situation?

Forum Responses
(Architectural Woodworking Forum)
From contributor M:
I have not had that problem, but it would not surprise me. What brand of MDF did you use, kind of glue, laminated or painted, exposed to high humidity? How many hinges, size of door? We need to know more to help.

From contributor D:
I don't build doors out of MDF, but keep a few sheets around for use as a CNC spoilboard. The whole idea that MDF is stable is absolutely false. It moves on the table, cupping this way or that, depending on humidity. I can tell because my through cuts are deeper in certain areas at different times of the day. A couple sheets left out on the loading dock one night got some light misty rain on one side - they curled up like a potato chip. One got soaked, and looked like big puffy flakes twice its original thickness, like it exploded into mushrooms. I read once that sealing your spoilboard edge with yellow glue was pretty popular. Well, I tried that and my 3/4" spoilboard swelled over 1/8" around the edges and curled up about 1/4" off my grid. So, whenever I read about folks using MDF because it's more stable, I always ask myself, more stable than what? The Trupan ultralight MDF I use is, density-wise, about halfway between normal weight MDF and normal weight LDF - probably most of my problem. Still doesn't give me a warm fuzzy feeling about using it for doors.

From contributor C:
I haven't done any 1 3/4" doors out of MDF, but I've done this size using 6mm triply that's down to a good moisture content. I do construct a lot of 3-4cm doors out of MDF for cabinets. The core structure is the same: a simple ladder of #2 pine, built up where there might be hardware. You want your pine to be straight and before gluing the faces, you want to drill vent holes in the top and bottom and let-in saw kerfs halfway through your sticks to help reduce tension. We use a normal PVA glue. We'll glue up on a flat surface, perhaps pinning, sometimes 4-6 doors at a time, and place weights (I've 1" steel plate 18" square that must weigh 60 lbs each) for 6-8 hours. You want to make sure your faces are balanced with the same MDF, paint, etc. Where I might get into trouble is when the client wants a full-face mirror on the outside. Then I have to be careful of the type of glue I use and how much, as the moisture content of the glue will pull the door out of plumb.

From contributor J:
I am a big fan of using MDF for my paneling and trim. Any areas that need a nice glossy coat of oil based paint, or trim that gets painted or covered.

That said, I would never use MDF for moving parts, especially doors. The exception is cabinet doors, but even then I don't like it. Exterior doors - forget it. I agree, MDF is relatively stable, but under stress it can easily cause problems. Especially for exterior doors, which get different temperatures from both sides of the door.

I had a client insist I put up MDF bead board out under his enclosed porch. I told him it would fail, he didn't care, he wanted it done before a home tour. Well, it held up for the tour! But even pre-primed, it warped like a potato chip all over the place. Even with liquid nails. MDF is just a poor choice for outdoor applications.

You never specified if it was an exterior door, but at 1-3/4" I assume it is. Stick with wood. MDF hates exposure.

From contributor A:
Agreed. If you need paint grade, use poplar. Much lighter too.

From contributor I:
Any material should be balanced. If you unbalance it in any way it will warp, sooner or later. If you machine doors from one side, you should do the same from other, or laminate, or even paint. Based on my experience, MDF is the most stable material that exists. Other good way to avoid warp is to create some sort of engineered core. Let's say alternate materials such as wood and MDF.