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Insulated Ladder Core Entry Doors for Workshop2/23
I'm building a backyard workshop for a friend, on a strictly as-available basis. As a result, this is not a typical contracted client situation where I might sub out work like this for fear of getting it wrong. He wants me to build the entry double doors, and he and I understand that if it doesn't work out perfectly, oh well. He'll just buy a set of pre-hung doors and we'll install those.
These will not be oversize, just a pair of regular residential-size entry doors.
I know there are a number of threads already on the subject of doors of this type, from which I've learned a great deal. I'm hoping David Sochar and others can fill in some of the details I'm missing.
As I understand it, traditional construction uses solid wood for rails and stiles, with mortise and tenon joinery. I believe I also saw that ply is also acceptable for the core, albeit possibly overkill. If I am misunderstanding those points, please correct me.
The insulation is rigid foam, cut to size to fill the openings in the frame, and sandwiched between the interior and exterior planks. The insulation thickness should match that of the core so as to eliminate any air gap.
3/4" vertical tongue & groove planks form the interior and exterior surfaces. The planks are secured to the frame in such a way to allow for seasonal movement. I have seen reference to gluing and/or nailing as attachment methods. An appropriate gap is provided between adjacent planks to allow for expansion.
If the planks are glued to the frame, how is that done in such a way as to allow expansion? I've built cabinet doors with floating panels, but those are edge supported, unlike this situation. Is there a single vertical bead of adhesive per plank to facilitate expansion?
Given that the tongue & groove mating surfaces are necessarily unsecured to one another, what, if anything, goes into the groove to prevent moisture entry, either as wind-driven rain or simply capillary action? It strikes me that an appropriate caulk might be well suited.
Do these doors typically get a separate edge treatment, or are the separate edges of the core and planks left exposed? If there is typically an edge treatment, is the bottom edge treated any differently? Given the contour of the plank faces, it would seem that you would have to make sure the exterior surface does not terminate at the bottom with a contour that would trap moisture.
Finally, I'm open to any and all suggestions as to a top coat over a solvent based stain. The doors will likely be under an overhang (that's a design detail that's still being hammered out), but they will certainly be exposed to some direct sun and moisture.
Many thanks in advance to any and all who are willing to share their experience.
I think you have a good plan.
I like solid wood for the ladder core so the stile sides are all the same species - looks good and will take hinge screws well, etc. It is a good chance to get rid of the 'wood of less desire'. We will try to make the T&G faces at 5/8" and then the core is 1" just so it feels a bit more stout. But 3/4" all the way through is fine also. Long tenons, please.
We glue the boards on the frame full width. The planks are generally no more than 6" and are often rift. So, I'm betting they don't move. V-joint is the norm, and the small area that almost meets is a good crush zone if/when the boards expand.
25 years ago, slaving myself to the rules, we stood on our heads for this one door, and only glued the center of each board. 1/4 of the width had glue and 3/4 did not. The edges curled up about 1/16" all along every T&G. The planks were cupped, with their centers down at the glue. It was a wine cellar door, so weather was not a problem. The door had been moved, unfinished, moved again, etc. No one complained, and I never looked back.
We may pin a starter plank in place, but the planks are added one at a time, with spacers on a flat bench. Flat bench repeated for effect. Start flat, stay flat, I always say.
Caulking the T&G can be hairy - too much caulk will either make a mess or prevent the boards from going where you want. We gave it up long ago. We make the T fat to the G and they are a tight fit - must be hammer tapped or clamped to pull them together to the spacers.
Insulation can be run thru a wide belt or even a planer. The side to sides should be real snug so as to be air tight.
The vertical edges will be made of the the three layers of wood. The top and bottom should be cut to size and then painted with epoxy to prevent water absorption. This is the one thing you can do to really help the life of your doors. Painters never 'seal' the tops and bottoms, so you might as well do it. Wd like Sikkens for the exterior. Remember, darker finishes age faster and can heat the wood. Heat can even cause a glue like TBIII to loose more than half its strength at 170 degrees. UV is harder on the finish than rain. Overhangs are not only friendly to your doors, they are nice for guests to duck under while you open the door.
My remarks above are suited for a full plank door as in the photos. Any horizontal rail will complicate things on exterior work. You do not want v-joints or panel gaps allowing water into rail plows.
That was extraordinarily helpful! Many thanks for taking the time.