Which Glue: Polyurethane or Epoxy For a Fence Gate

[William Hodge]

I work on restoration projects where epoxy has been used over wood that gets wet, like historic fence restorations.
The wood moves,and the plastic epoxy doesn't. Water gets under the plastic. The wood discolors and rots. The plastic comes off in sheets in some places, in others it sticks.

Build a traditional gate, through mortise and tenon, pegged and wedged. Everything will be flexible enough to handle the normal wood movement of a gate out in the weather. There will be wood movement, the wood will weather. It's a garden gate, not a library cabinet.

[Lee Schierer]

If you decide to use polyurethane glue, don't wet the pieces before assembly. Wetting the wood makes the glue foam a lot. I just apply the glue and clamp things together while it sets. There is enough moisture in the air and in wood even at 7% moisture levels to set the glue. It still foams a bit, but not nearly as bad as when you wet the wood first. I have yet to have a joint that I put together dry fail and they are impossible to get apart without destroying the wood.

[Jimmy Harris]

They're pretty much equal in this situation. Well, polyurethane glue will expand as it cures, and that could cause issues, but not if you use it right. And it could be a benefit in some cases. Either way, the main problem I see is wood expanding and contracting and the adhesive being brittle enough to break free of the wood. Depending on a bunch of factors, it may or may not be an issue.

Personally, I'd be tempted to go with Titebond III if you're not going to use a mechanical connection like a drawbore. I'd be more worried about expansion and contraction than water resistance. The M&T joint itself should shield most of the adhesive from direct water contact, so it would less of an issue than in something like a butt joint.

[Doug Garson]

I honestly can't think of a worse adhesive than silicone for this type of project.

Maybe hide glue?

[Bill Howatt]

I made 2 36" soft wood wagon wheels, on one I used epoxy to fasten the spokes to the hub and rim, on the other Gorilla Polyurethane glue. Both have stood up equally well for about 20 summers.

[Andrew Hughes]

Think of silicon as a gasket to keep water out not so much a adhesive. Outdoors build should have tight joints that gives it strength draw bore or big ugly screws.
Water is the enemy of outdoor projects.
Epoxy is probably the best for gap filling and strength. Not idea with soft woods like Western red cedar.
Too me relying on Titebond 3 as a outdoor adhesive? Not good.

[Jimmy Harris]

Think of silicon as a gasket to keep water out not so much a adhesive. Outdoors build should have tight joints that gives it strength draw bore or big ugly screws.
Water is the enemy of outdoor projects.
Epoxy is probably the best for gap filling and strength. Not idea with soft woods like Western red cedar.
Too me relying on Titebond 3 as a outdoor adhesive? Not good.

Why not Titebond III? I've got some planters that have been sitting outside for 7 years in the intense sun, heavy rain, 80+mph winds and temperatures running from 0° to 115°F and they've held up fine. They're made out of pressure treated SYP so it was pretty green wood to begin with, and they've definitely seen their share of warping and stress as the wood has air dried after assembly. My father used it to build his pergola 15 years ago and it too has held up fine. I've even used it to repair a wooden ladle that's routinely submerged in boiling soup.

That glue was designed for outdoor use. I know I've seen some YouTubers run tests that suggest otherwise, but from my personal experience, it's done exactly what the manufacturer said it would.

[Andrew Hughes]

I’ve not had good results with titebond 3 outdoor with curved lamination glue up.
Are you saying titebond 3 is the only thing holding your planter together? No fasteners or mechanical advantage with the wood?
Epoxy is the only adhesive I’ve seen that soaks into wood and create a strong lasting bond.
Gorilla glue that foams and expands is messy I’ve used it with better success the titebond 3.

[Todd Zucker]

I used West System g-flex epoxy for mortise and tenons on an outdoor table teak table in 2017. It sits in direct sun and gets rained on frequently and has held up fine.

I used System Three T-88 more recently as well on an indoor table.

Both say they are non-brittle. The curing process is a little strange compared to regular West system epoxy, as it hardens slowly. Makes you think you might have mixed it wrong but ends up fully cured overnight. Maybe worth a look for your project.

[mike stenson]

Maybe hide glue?

It'd work as a great lubricant for those draw-bored mortise and tenons.

Then again, so would epoxy...

[George Yetka]

Total boat Thixio They have a few different options. Ive used it a few times now to good results

[Jimmy Harris]

IÂ’ve not had good results with titebond 3 outdoor with curved lamination glue up.
Are you saying titebond 3 is the only thing holding your planter together? No fasteners or mechanical advantage with the wood?
Epoxy is the only adhesive IÂ’ve seen that soaks into wood and create a strong lasting bond.
Gorilla glue that foams and expands is messy IÂ’ve used it with better success the titebond 3.

Yup. Just dowel joints with Titebond III. I wouldn't trust it for a butt joint outside, as the edges would be exposed to too much water. But so long as the joint is somewhat hidden so that water isn't allowed to pool up on it, it seems to do just fine.

The curved lamination could be the source of the problem you experienced, as the edges of the lamination would be exposed to the rain and could allow water to pool up on them, I assume without seeing the project. Also, when gluing up a stressed joint with TB3, I always allow plenty of time to cure before removing the clamps. The recommended time of 24 hours would be on a warm day with dry wood. If it were a cool day or the wood was kind of wet, I'd probably leave them on for up to 72 hours, if the conditions were bad enough. TB3 is a little more picky that most wood glues about drying and curing times, in my experience. I also often thin it with a bit of water, especially if it's been used before, so that it'll soak into the wood. A fresh bottle will show you the proper consistency, and it tends to thicken up over time. So sometimes you have to counteract that. But it's my most used and trusted glue and it hasn't failed me once. Which is how it's become my most trusted glue.

But if it has bit you before, I wouldn't blame you for not liking it. It's hard to trust a product that's failed you before when you've put a month's worth or hard work into the project. And it's certainly not always the best choice.

[Michael Burnside]

I wouldn't say TB III is a "bad" choice, but IMHO it would not be the best choice unless you were trying to save money. In just about every way epoxy is a superior product for most outdoor applications once you learn how to properly work with it. It's actually quite simple and a little goes a long way.

In fact I prefer it many times for indoor projects, particularly for long waterfall miters, tricky glue ups or particular types of wood. My recent project that utilized roasted oak, TB III/II broke apart even after sitting for more than 24 hours with just a little hand force. I just did it as a fun scientific project since I had some scraps. It's not the glue's fault, I understand carbonized wood makes it hard for TB III/II to work properly, but it also demonstrates how good epoxy is in contrast.

[Rod Sheridan]

I’ve not had good results with titebond 3 outdoor with curved lamination glue up.
Are you saying titebond 3 is the only thing holding your planter together? No fasteners or mechanical advantage with the wood?
Epoxy is the only adhesive I’ve seen that soaks into wood and create a strong lasting bond.
Gorilla glue that foams and expands is messy I’ve used it with better success the titebond 3.

Hi Andrew, I have outdoor raised bed planters made out of 24” square patio stones stood on edge, buried2” in the ground.

The top has a cedar frame around it, made with mortise and tenon joints, and Titebond III glue.

7 years of freeze/thaw cycles and they’re still perfect.

IMG_0596.jpg

Regards, Rod.

[Andrew Hughes]

Well that’s great I can see your pics and understand. Could it be the joinery is holding it together?
I’ve made planter boxes too I don’t remember using any glue they held together fine. They held dirt grew plants everyone was happy. I guess I could have used glue ,silicone or even hair gel and been successful.
I think the op was asking about a gate I’ve made lots of gates. Water intrusion is the main problem with outdoor stuff.
I don’t have a pic but I made a gate entry with a arch above. The titebond glue failed it delaminated all the glue line were exposed to elements. It was a brick lay glue up like what’s being discussed in that other thread.
I still stand with my original statement I’m unswayed by your robust looking planters sorry buddy.
Good Luck Always