Cupping Door Stile

A moisture-related wood movement problem leads to a discussion of LVL versus solid wood core material for veneered exterior doors. August 6, 2008

I just came from a job site where one of my door stiles is cupping and cracking. It is 6" wide and 2" thick, LVL core edgebanded with 3/4" VG Fir and face veneered with 1/4" VG Fir. It is an exterior door with perhaps 2-3 hrs of sun. Would lumber core be a better choice and if so why? This is the second time this has happened and both times it was an exterior door. Any feedback would be appreciated.

Forum Responses
(Architectural Woodworking Forum)
From contributor A:
Balance the face veneer with the same on the backside.

From the original questioner:
Both sides of the stile are veneered with VG Fir if that is what you are referring to.

From contributor B:
I imagine the issues are all moisture related. LVL is not very dry or stable for that matter. VG Fir commercially purchased also has high moisture content which could be contributing to the problem unless you have dried it or at least checked it prior to working. We have ripped and flipped LVL in the past so it is 90 degrees to the face for what I believe is a more stable product but the compressed plies can expand upon the first increase in moisture. We do not mess with LVL anymore but stick to all wood stave core. Check out an old topic: Knowledge Base Article

From contributor C:
I have done both types of core, and the face veneers have varied from 1/8" to 1/4" per job with no real effect. LVL is great for construction, but the compressed state that makes it strong also makes it weak as a core. To paraphrase the points made in the database thread, it is just a compressed sponge waiting to spring back, just add water. Shop laminated lumber core of cull grade SPF that is MC compatible with the face stock is the safest core I've used. If MC changes or thermal expansion occurs, these materials move in relative harmony.

There is one other related factor in door stability that I have seen with chronic repetition. Doors are installed unfinished or have the finished edges shaved to install. Whatever the reason, the finish person never removes the door to seal the bottom edge, leaving it raw and open to moisture wicking right at the floor where most moisture is encountered.