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I have a bunch of 5/4” x 6” x 8’ severe weather pressure treated boards from Lowe’s and was going to wood glue them together and then trim it out with 3/4” x 4” pressure treated wood boards I have. I figured that would also help keeps the boards together. However all the plans I’ve seen online for barn doors seem to be inside the house and not outside and are sliding doors where mine will be hinges as it’s for a shed. Will pressure treated lumber like this work well or is this doomed to fail as the wood glue (titebond ultimate) may not work and the trim isn’t sufficient to hold together. The doors will be approximately 3ft in width and 7ft in height. Hinges will be at the top , bottom, and mid section.

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The fact that the lumber is pressure treated isn't really a problem for you. The problem is likely related to the moisture content of the boards.

I don't know how old the lumber is, etc. but one of the challenges with newly-purchased pressure treated lumber (especially from the Big Box places) is that it's almost always wet. Very wet. Too wet to glue wet. Wet where water (or chemicals maybe?) will drip and run out of the wood fibers when you drive a screw into them.

The glue itself should bond fine as long as you provide dry, clean and flat wood surfaces to glue together. Exterior grade glue will work like a charm under those circumstances, but the right way to do it for doors (since they are subject to the stresses of being moved, etc.) is to use galvanized, stainless or ceramic-coated screws as well to hold the door together.

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The problem is, especially with an outside door, because the wood is out in the elements, it acquires and loses more atmospheric moisture which causes the wood to swell and shrink more than an interior door.

Glue isn't going to really help you here as the moisture-related expansion and contraction isn't going to "play nice" with the glue joints. As the wood moves, it moves across the grain of the wood and the movement can be significant as the moisture level of the wood changes to the point that the door can tear itself apart.

At the center of the boards, the movement is less than from edge to edge. Screws, when attached through the center of the boards (where moisture-related movement is minimized) should work very well.

Tongue and groove profiles are sometimes cut into edges of the battens (vertical boards) so that they lock together and as they expand and contract, any gaps between the batten boards are dealt with. It isn't 100% necessary, but it is a nice feature. You can cut tongue and grooves with a router and appropriate bits.

Here's a tutorial that explains it better than I do.

And another one that's very good (and thorough) too.

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    Also: As mentioned, it seems that the fad for making interior doors that roll on tracks has entirely hijacked the term "barn door" and as a result it's hard to find information on doors for barns. I had a lot more success searching shed doors. J/s.
    – gnicko
    Jan 27, 2022 at 1:04
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    Plenty of actual barns use sliding doors.
    – Ecnerwal
    Jan 27, 2022 at 1:36
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    As with most inexpensive things, they put a designer label on it and it gets expensive.
    – crip659
    Jan 27, 2022 at 2:02
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    If you add screws I would say it would work well. Glue and screw can make a durable product on most wood projects, I have 11 sliding barn doors and even more hinged and Dutch doors without screws I would have piles of board pieces but my barn is a working barn the horses are tough on them.
    – Ed Beal
    Jan 27, 2022 at 2:18
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    @IrishRedneck the amount of drying time depends on how wet the wood is now. It might take a couple of months, it could take significantly more. If you're willing to wait, you could put your old warped door back on and cover it with a tarp for temporary water proofing. If you've got room, you could bring the wood into the house (where it will be warmer and probably drier) for faster drying than in the likely cooler garage (it's up to you to determine how to get this approved by other house residents ;).
    – FreeMan
    Jan 31, 2022 at 18:38
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This answer is highly related and will provide many good tips on building your door correctly the first time. In particular, pay particular attention to the bits on gluing/screwing the bracing to the back. (TL;DR: do not glue the bracing to the back!)

Your Titebond III should be just fine - it's waterproof which is what you want for an outdoor project. However, from the "Limitations" section of their product page:

Because of variances in the surfaces of treated lumber, it is a good idea to test for adhesion.
Emphasis added

I went to look up "Titebond Ultimate" because I've always referred to it as "Titebond III" and wasn't sure if they were the same product or not. They are. Technically, it's "Titebond Ultimate III". Enough product promos for ya'? :)

If you let the PT lumber dry (probably 3 months, depending on your local humidity) and get a good, straight, freshly sawn (or even better, a jointed*) edge, your glue up for your panel should be just fine.

One thing to consider, though, unless you need the door to be absolutely water tight, you may not need to glue your door panel at all. Just be sure your decking (that's what your 5/4" x 6" was sold as, right?) has good straight edges, butt them tightly together as you screw your bracing on the back, then put a waterproof layer on the inside of the door to catch any moisture that makes it through and direct it back out and it should be fine.


*You can get a jointed edge with a jointer, of course. You can also use a jig on a table saw, a powered hand plane, or even a good old-fashioned hand plane. Many will argue that you will get the job done with a hand plane faster than you can set up the work on any of the power tools. Don't forget, though, that there may be sharpening time prior to hand planing and, possibly, during if you're doing enough work - they don't seem to count this into the speed comparison. ;)

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  • It would perhaps be better not to glue the boards together in an exterior environment. If seasonal expansion/contraction goes to work on a large panel, it will compound the movement seen by individual boards. Ship lap or tongue and groove will allow for things to move but keep any gaps, etc. closed.
    – gnicko
    Jan 27, 2022 at 19:32
  • @gnicko that's addressed in the linked answer.
    – FreeMan
    Jan 28, 2022 at 12:02
  • Yep. (That linked answer is fantastic!)... Just restating that gluing the boards into a panel is probably not the best move here. You are absolutely right that the PT lumber should glue up just fine if its jointed (or close to it.)
    – gnicko
    Jan 28, 2022 at 17:20
  • @FreeMan would you glue the tongue and groove joints? Sounds like screwing the back bracing without glue is best but what about the vertical joints?
    – Qiuzman
    Jan 31, 2022 at 18:37
  • If you go T&G, no, there should be no need to glue. Get a decent quality product out of a weather resistant species (like Western Red Cedar, or others) and you don't need to PT the lumber in the first place. Do consider the season you're building in when sizing. If you build now (winter, Northern hemisphere), your wood will be small because it's dryer in the winter - err on the side of expecting the wood to expand.
    – FreeMan
    Jan 31, 2022 at 18:42

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