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Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Veneered solid-core doors Question
- Laminate core using (2) sheets of 11-ply Baltic birch with West Systems/Unibond 800. Vacuum press.
This seems like it should create a very sealed, stable exterior grade plank-like door, but any feedback is appreciated (i.e. core construction, glue choice, finish). Forum Responses
From the original questioner: I will be veneering both faces the same to create a balanced panel (vacuum press). How about the idea of using a solid core pre-fab door slab as my core and then laminating to it? Any pre-fab cores known to be better then most? I'd go for exterior Douglas fir ply rather than the birch, but it sounds like you're prepared to do a high quality job. From the original questioner: Is the fir more stable? The birch is actually 13 ply, not 11 ply and is pressed using exterior grade glue. I'm also building the jambs - solid 8/4 teak with rabbeted stops and was wondering about the head to leg connection. A rabbet with screws? Or maybe finger joints? Looking for long term durability. We have put thick veneer on solid core exterior door slabs with a vacuum press. Stable but also very heavy. Also have used two pieces BB 9 ply fir exterior plywood with good luck. BB is a balanced construction and a little better than most plywood for warp. Seems like the Baltic birch ply is unstable. From contributor D: We build slab doors like this quite often. Some people call them castle doors. Once you have the method down, they can be arched, with window openings or grates, etc. We do this only as a 3 ply affair, usually 2-1/4" to 3" thick. The center core is a full mortise and tenon empty frame - no panels - with lots of cross rails (every 6"-8" or so, but only 2-3" wide). Long accurate tenons (haunched at either end) and very flat, 3/4 min. to 1-1/4 thick. Then make t&g faces for each side. We fill the empty panels with rigid insulation. Pin or tape the faces on each side (leaving expansion room at the joints), and glue (epoxy if teak) and slide into the bag. No need to edge band if you use the real thing throughout. Regarding the jambs, we rabbet the sides onto a solid canted sill and the head, glue and lag. Then fit the door and swing, then latch. I found this method is what works on lots of 50-75 year old doors here in the Midwest. They are still up and looking good, yet all the plywood and skinned doors, veneered doors, and others all are falling apart rapidly. I would stay away from commercial cores (no ext. glue) and plywoods. I have learned to trust good solid wood and good solid craftsmanship. I think the epoxy finish is overkill unless you are fronting the North Atlantic - what happens if someone has to trim an edge? We see great results with a Sikkens system. And yes, this will be heavy. Eat your Wheaties.
I like the sound of the method above. How thick are the panels? From contributor D: There are no "panels" - as in raised or flat or whatever. The door is a 3 ply affair with 3 plies of 3/4" each. The center is a mortise and tenon frame of stiles and rails that holds things on size and gives a surface to mount the outer plies - t&g skins - onto. The tenons need to be long and deep and accurate to hold the skins in place without sagging. I meant the thickness of the "skins." Of course, I understand the construction method that you have explained. Is there a rule of thumb that you use for determining the skin thickness vs. the core thickness? From contributor D: I may be all thumbs, but the rules are not well established. I think the core should be as thick as possible/practical to carry all the weight, and the skins as thin as possible/practical to give a good t&g and keep each other flat. In practice this amounts to 3/4" to 1-1/2" core and 2 - 3/4" plies of t&g for net of 2-1/4" to 3" on exterior work. Some interior wine cellar doors get down to a 5/8" core and 2 - 9/16" shiplap plies of facing. The interior door can stand the shiplap since the environment is relatively stable. The two elements of the door (t&g and core) have two distinct functions and work differently from each other. Just as in frame and panel where the frame does the work and keeps things on size while the panels just fill holes and keep out the rain and raccoons, the core needs heft to carry all the weight of the faces. This "beef" is accomplished by three strategies: 1. as thick as possible/practical, 2. 40% or so of the height is filled with horizontal rails, and 3. the rails have long tenons (2-1/2" to 3-1/2") to yield lots of surface area for glue as well as racking strength. One thumb rule to keep handy is that the tenon should be approximately 1/3 the thickness of the stile with the mortise. These doors are nice because you can add some vertical rails in the core and make openings for windows or speakeasies by adding rabbetted stops to the opening perimeter. We have even done a couple on radius to fit into curved walls - one with an arched head.
How do you attach the t&g skins to the frame? Did you say you press them on in the bag? How is the edge treated? Do the 3 plies bond to appear solid? Thanks for your descriptions so far; very interesting. From contributor D: The t&g are pinned if needed - just to hold in position, urethane glue everywhere, and the whole shebang into the bag. The stile edges look fine once edge planed, and the top/bottom trim off nicely. Make the assembly 1/2" long and 1/4" wide and it will all trim down cleanly. Screws and plugs can be used on one side or both if the situation warrants, or for decorative effect. This can be done without a press, with cauls and clamps, but is a lot to handle. Must be done on a leveled bench or supports to start/stay flat whether a clamp up or vacuum bag.
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