Exterior Door Core Material and Moisture

      Which will handle moisture changes better, LVL or solid wood door cores? February 8, 2008

I had some bad luck doing two-piece stile glue-ups. Short of throwing them away, I'd like to re-saw to make 1/4 veneer and use an engineered core. What is the difference between stave core and LVL, and which will hold up better for exterior doors? I'm having tons of trouble with wood movement due to moisture in the air.

Forum Responses
(Architectural Woodworking Forum)
From contributor D:
If you are having moisture trouble with solids, the LVL or stave core will not be immune from moisture trouble, nor solve your problems. You should look to control the moisture problems first. Insure that your lumber is proper MC, and your shop has stable humidity. Dissimilar materials, with dissimilar moisture content, will multiply your problems. And if you are having problems now, wait until that door gets out in the weather. What is the MC of your solids? What is the relative humidity min and max in your shop?

From the original questioner:
Yes, you're absolutely right. I jumped the gun using lumber that came from a dryer area without letting it get a proper EMC. My area is much wetter this time of year. Being that my shop is in a wetter area and my products generally go to a dryer area, I would like to go to a more stable core, but still am unsure of the pros/cons between stave and LVL core.

From contributor T:
If it matters to you, LVL - or structural composite lumber - cores are not recommended for exterior use by AWI Quality Standards. Lumber cores have been around a lot longer and have a good reputation for success. LVL cores may very well be a superior product, yet there is insufficient data to support that at this time.

From contributor G:
Contributor D, do you build doors? If so, what standards do you apply to the lumber cores that you use? I have had problems with LVL cupping with extra wide stiles but no one seems to be able to offer much criteria on lumber (stave) cores. Should the core material be the same species as the face veneers, what size should the lumber be, etc.

From contributor C:
We build doors this size all the time, and the problems aren't so much MC in the wood or relative humidity in the shop as what happens once the things are installed in the field. You can say the doors need protection from the weather and need to be finished within 7 days until you are blue in the face. It does no good. I have found that a linden (basswood) core with at least a 1/4" veneer is the most stable. We often use stave construction, but have used solid linden quite often with no callbacks. LVL is easier, but one warped door and the customer goes elsewhere.

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