MDF Panel Door Warping Issues
How to anticipate and minimize warping in a large MDF frame-and-panel door. July 12, 2008
I am doing a job in which the architect is requiring a frame and flat (MDF) panel door be approximately 25" wide and 100" tall. I want to let him know ahead of time the warp tolerances to expect and have him accept this as not an execution problem. I checked with Conestoga to see what its tolerances are for this size door and looked in an old AWI book to see what they had listed. I was not able to find anything in AWI. Is there an "official" source that I can refer to on this question?
(Architectural Woodworking Forum)
Can't help you with the warp sources, but you might be able to minimize some of the panel warp by making a thin torsion box. 1/8" MDF skins over honeycomb core and you could make a strong, light, flat panel fairly quickly.
From Professor Gene Wengert, forum technical advisor:
If you are making the door, consider putting a stiff piece of metal rod in the door frame (or two) to help prevent warp. You are indeed correct that warp is to be expected with such a large item when the MC changes. It would be more severe for an exterior door which will have perhaps 12% MC or higher on the outside, but 7% MC or lower on the inside.
From contributor A:
If I understand correctly, your door is a shaker type. We make lots of doors in MDF between 80 and 96 inches tall, and don't have any problems with warping. Use moisture resistant MDF for all components, make sure your boards are flat before you cut them up. 22mm or 25 for framing, 9mm for panels. Glue it up flat, store it flat, use enough hinges and there shouldn't be a problem. We spray prime them all round, and spray white pre-cat on the backs, leaving the fronts for hand finishing on site. The panels are usually set out of centre in the door thickness. These factors would, I think, make the doors more likely to warp, but still no problems.