To glue or not to glue?

[Dan Russ]

I build lots of these barn doors for my customers and lately the larger doors have been cupping on both ends of the door. I use build a frame by using pocket holes and then glue and nail the tongue and groove boards to the back of the frame. I put glue in the grooves as well as where the boards meet the frame. I have been told that I should not be gluing the groove to allow the wood to expand and I am aware of that but I guess my question is, is that whats causing the doors to cup? Also, the doors are pre finished weather it be stained or painted. If the wood expands, then wouldn't the bare wood of the tongue be exposed and need to be painted and or stained? I don't see a good way to build these doors and not have either one of these issues.



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[Dave Zellers]

ixnay on the uglay.

Make the frame side structural, pocket screws (hate them) or M&T. Then screw through one edge on the T&G side. No glue.

This is a fancy board and batten door. You never glue battens on a board and batten door.

[Joe Adams]

The problem with your doors is wood movement due to moisture level changes is being restricted by their construction.

Your design has to allow for movement.

Are you testing moisture levels before you start?

Also, make sure all six sides of the door are finished. The top and bottom of doors are often skipped. Your photo of the ends does not appear to be finished.

[Jerry Miner]

+1 on no glue in the T&G joint. The individual boards need to be able to expand contract individually (That's the advantage of T&G).

To solve the exposed unfinished tongue issue, you can pre-stain and finish the tongues before assembly.

[Sam Murdoch]

+1 on no glue in the T&G joint. The individual boards need to be able to expand contract individually (That's the advantage of T&G).

To solve the exposed unfinished tongue issue, you can pre-stain and finish the tongues before assembly.

^ Here you go. Problems solved.

[Charles Lent]

+1 for the floating panels. Only glue the rails to the stiles with water proof glue. Epoxy is best. All 6 sides of the door need a water resistant finish.

To keep the rails and stiles straight I've learned to use only quarter sawn, or nearly so, wood. If flat sawn, they will cup and twist with any moisture changes. I now do this for interior cabinet doors as well.

Charley

[Dan Russ]

These are for interior use only and I use construction grade lumber. The profit margins would be too small if I had to mill up my own lumber.

[Dan Russ]

I would love to be able to use M&T but the lumber is only 3/4 thick.

[John Blazy]

the rail on top is bowing due to the drying out of the glued T&G boards bonded to it. You say you are installing these in interior only? The lumber you are getting has likely been kiln dried down to 10% ish, but when stored in the lumber yard or big box store where you got it, it absorbed ambient air moisture and hit equilibrium moisture content, which is about 15 to 20 % (or more in the spring). Then you built the doors and installed them or stored them indoors of a house or shop, and they dried out again from higher moisture to a lower moisture content, thus shrinking, and bowing the rails.

Do as everyone else says here and your golden, but I would add that you need to nail or screw (covered with plug) in the MIDDLE of each T&G board so they expand/contract from ONLY ONE bond point. You will never get bowing again, assuming you never glue the tongues in their grooves, like was suggested.

[keith wootton]

if your doors gain moisture from the air, and your tongue and grooves are tight, your doors will bow the other direction. i can imagine the total expansion and contraction in your tongue and groove side being 1/2" in an interior situation.

keith