I am making a standard size slab style door from VG Douglas Fir. It will be hung in a trimless aluminum frame and will incorporate a rabbet detail on sides and top, final thickness will be 2". Located in San Fransisco, it faces north, and is recessed in an alcove.

Having read many of the door posts on this forum, I've settled on the following approach: Ladder frame with 5" stiles and 5 or so rails joined with stub tenons + xl dominoes (could do full M+T if need be. would rather not). Voids filled with rigid insulation, skinned with 1/8" marine ply. 1" rail applied on both long sides, lipping planed flush. 3/32" shop sawn veneer (or 1/16" from certainlywood) applied over that. Marine ply and veneer to be glued using west systems epoxy in a veneer press. Would rather not use resorcinol but could be swayed to a pre catalyzed urea resin glue or polyurethane glue.

Finish has not been decided, though I am leaning toward spraying something like GF Exterior 450.
As has been my experience in the past, client does not love the appearance of freshly milled fir, and is looking for a more amber tone. One thought I had was to leave unfinished door in the sun for an hour or two, another though was to let the sun do its work over time. I will also be supplying a small run of T&G siding to match door for the alcove, ideally sprayed with same finish.

Have made exterior doors, but never a veneered one. Have done plenty veneer work, but not exterior. Does this approach seem sound? If there are any other finishes you can recommend, or any other pointers or admonitions, much appreciated.

-Revel

Your approach to building the slab-style door with VG Douglas Fir is solid: using a ladder frame with 5" stiles and rails joined with stub tenons or Dominoes, filling voids with rigid insulation, and skimming with 1/8" marine ply is a robust choice. Applying a 1" rail and lipping for a clean finish is smart, and using 3/32" or 1/16" veneer with West Systems epoxy will ensure durability. For an amber tone, exposing the unfinished door to sunlight can help, but a controlled stain might offer more consistent results. GF Exterior 450 is a good finish choice for durability, and spraying the matching T&G siding with the same finish will ensure uniformity. Test the finish on scrap wood first, and make sure all edges are sealed well to prevent moisture issues.

thank you 'fir' your response, and the finishing advise is much appreciated.... only thing I'm worried about is the strength of those voids. once that foam is skinned (rigid pink XPS 1.5") it will effectively be a torsion box, but it would seem you could still kick / punch a hole through if so inclined. SO I'm wondering if a true torsion box would ameliorate this potential issue ala the way David Sochar and others have illustrated; egg crate construction with voids filled with foam. the marine ply is hydrotek, and closer to 3/16"... I would use a thicker skin, but was constrained by the foam thickness (either 1" or 1.5") and the overall door finish thickness (2"). Don't want to over think this door, but don't want to deliver a flimsy product. I suppose I could vac bag a prototype panel. Another little wrench in the gears is that now the client does not want a typical aka functional threshold, but rather wants no threshold. Told them how this was silly and we had a chat about water etc, and now we are looking into drop down door bottoms from pemko... but that won't solve the water shedding issue. Going to work on this a bit more

Your approach to building a slab-style door from VG Douglas Fir sounds well-considered, especially with your detailed construction method. The use of marine ply and shop-sawn veneer with West Systems epoxy is solid. For a more amber tone, allowing the sun to naturally age the fir could work, but you might also consider using a UV-stabilized finish to maintain the desired hue over time. GF Exterior 450 is a good choice, but also consider spar urethane for added durability. Given your experience, your plan seems sound, but keep an eye on the moisture resistance of all materials and finishes used.

My apologies for trashing this post.
Management can delete it all, I’ll clean it up and repost.
The edit is a good feature, but I could not edit all of my post, only one paragraph.

Thank you, David. I would be very curious to see the rest of your post. Our vac table is pretty dang flat, my colleague Tim just gave it some tlc. I was going to ask-would you ever consider using polyurethane glue for an exterior door? I think the answer is probably no, but just checking.

Oliver- regarding a UV stabilized finish, do you have any recommendations. I have not had great experiences when trying to stain fir so I assume that is out. The client does not like that fresh milled fleshy fir color, and I imagine the inside surface of the door will retain that hue for some time. However, since I am matching this door to the surrounding siding (which I am also making) am inclined to not use any color as it will ease refinishing down the road

Slab glue up went ok, door has a 1/16" bow (not sure why, I'll double check that table) but no wind. I'll orient the concave side toward the lock jamb. Now for the veneering- Its all cut and thicknessed with the helical planer, somehow it didn't chew any of it up. I don't think I need to scuff sand it, and we don't have a wide belt but I'd run it through a friends if need be. I'm wondering how to veneer both sides of this at once
(I understand that is best practice with epoxy, as it shrinks a bit when curing?). Bottom side is a no brainer, then I have to veneer the top... I'm leaning toward edge glueing it first all first as that will take some variables out of the bag process. Wondering if edge glueing with epoxy is necessary, or if I can take a break from the stuff and use titebond 3 before I epoxy the resulting sheet onto the door core. Any ideas appreciated

No TB3, less you risk a failure. Heat causes failures in TB3, and those edges will hold the door up. TB2 or epoxy. And edges first is the way to do it. Both faces at once, tho that is hard to do.
You are smart to work with the bow. “Crowning” the door will hang the door with the concave side hitting the stops top and bottom first, then a bit more, and the latch snaps in and holds the door tight to the stops, no rattles, secure. If you are using the gawdawful compressible foam, all bets are off., and crowning is useless. Time was, all doors were crowned…….
And that errant photo. What is wrong with the elevation of that house?
Weekend in Branson if you guess correctly.

David- would a core of solid flake board be acceptable? Not perticleboard but basically a large sheet of LVL type material? The local molding and door shop that I cnc parts for uses this method for their interior and exterior doors that they send to the mountains ( Vail high end and harsh environment ) .

It seems a very quick and easy method for slab doors , however they are very heavy , but everything we have machines for them was very flat and true. I have a couple slab doors to make coming up and wondering about the viability of this methodology.

Shutters are backwards?

I opted to epoxy the veneer to the door without edgeglueing; I did both sides of the door at once, and it went very well. Though it adds a step, I would probably edge glue the veneer next time, and not with TB3 -very interesting btw, David, I had heard that before but now I think it's sunk in!

Re: LVL core doors, I looked in to that. I've surmised that if you are very vigilant about MC it can work and is certainly a labor saver albeit heavy as you mentioned. Whereas it will stay flat, LVL is still wood based and thus prone to some swelling / shrinking.

...Maybe those shutters are on some sort of horizontal sliding hardware haha 🤣

This post is in regards to TB3 and my experience.
I have done repairs on my cedar trim with west facing exposure. And after 10 years the glued joint still is fine. Another little project was making a laminated handle for a snow shovel. That was a a lot of time! Butthat was 15 years ago and when not out it is under the barn with a south exposure. Still holding.
So curious about these other failures.
Thanks

Meant to post some photos months ago- the door came out great. Install has been delayed but looking forward to that. I’ve sourced, milled and fillished some matching siding to surround the door in an alcove. I even saved veneer offcuts for the transom area. A fully trimless install, here’s hoping those walls are framed true as there’s nowhere to hide anything.

View higher quality, full size image (5712 X 4284)

View higher quality, full size image (5712 X 4284)

View higher quality, full size image (5712 X 4284)

Tom-I think it wise to err on the very safest side one can find. I also have a few projects around the compound glued with TB3 that have lasted for years.
However, this is no proof that the glue will pass for our commercial customers. Any failure in one of our products can result in thousands of dollars in repairs as well as a damaged reputation in the marketplace. Owning a small business is a gamble of its own. I do not need to add yet another variable to the mix.