Which Glue: Polyurethane or Epoxy For a Fence Gate

[Mike Ontko]

Howdy all! I haven't posted for a looong time, for reasons that I won't go into in this ask. But I am still making sawdust and pulling out the occasional splinter, so all is good.

I'm just starting a garden project for my daughter and son-in-law--creating a 600 sq ft space with 5 raised beds and a simple fence created with a 2"x3" wire mesh over a 2x4 panel structure (see the image below). My question pertains to the assembly of the pergola and main gate, which will be built with western cedar and joined using the trusty ol' M&T.

Given that both Polyurethane (Gorilla) and Epoxy would be water resistant if not outright water proof (which is a near-necessity in the PNW), which of the two would give me the best results where A) working time and B) durability are concerned?

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[Michael Burnside]

No question for me. Totalboat (or your favorite brand) epoxy with a slow hardener.

[Mike Ontko]

I've used Total Boat and the slow hardener as a finish coat for a past sign project (pic below), and still have some around. So, this is a definite possibility. But for joinery, would it be potentially brittle and not able to stand up to the flex forces that a gate might be put through?

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[Frank Pratt]

I wouldn't be concerned about the epoxy being too brittle. If it worries you, there are more flexible formulations of epoxy to choose from.

[Brian Holcombe]

Draw-bored mortise and tenon.

[Michael Burnside]

I've used Total Boat and the slow hardener as a finish coat for a past sign project (pic below), and still have some around. So, this is a definite possibility. But for joinery, would it be potentially brittle and not able to stand up to the flex forces that a gate might be put through?



I've used it numerous times on chair/table tenons without any issue. Never built a gate exactly as you're outlining but I personally don't see a measurable difference. If you're worried, do as Brian suggests and drawbore a dowel into your tenon after assembly.

[Mike Ontko]

Draw-bored mortise and tenon.

That's an excellent suggestion!

I usually prefer some type of mechanical connection over just glue, wherever it might be applicable. I used draw-bored tenons on a saw bench that I built just a short while ago but it never occurred to be to use it in this application.

[Rod Sheridan]

Hi, how can you drawbore something after assembly?

Regards, Rod

[Mike Ontko]

Hi, how can you drawbore something after assembly?

Regards, Rod

I imagine it would be fairly difficult, especially if glue had been used in that assembly process :D

Fortunately, I haven't even progressed any further than the planning and material purchase stage of this project, so there's still room for modifying the design.

[Andrew Hughes]

There’s another glue option for outdoor wood projects that’s not often talked about. Silicon caulk and polyurethane caulking. I discovered it from my roofing days doing repairs. Polyurethanes bond on a clean surface is brutal to remove wood, metal ,brick stucco, bricks.
Silicon is pretty tough too.
Good Luck

[Andrew Seemann]

Some of the polyurethanes are very strong and bond well to wood. Silicone not so much, especially when exposed to the weather. It sticks very well to to non-porous surfaces like metal and glass, but frequently can be pulled off of wood after a few years with just your fingers. We found this out the hard way using it to caulk between Lexan and wood & between wood and wood on greenhouses over the decades. I'm not sure if it was the UV light, expansion&contraction of the wood, or some chemical thing between the silicone and the wood, but bond failure was pretty consistent. In defense of the manufactures, they do say not to bed glass with it.

[Kevin Jenness]

Given the complexity of the design I would opt for slow cure marine epoxy for longer working time. Both glues will make a mess but epoxy can be cut with vinegar initially, then alcohol or acetone as it starts to cure. Either way it would be a good idea to prefinish the parts and do a dry run to test the glueup procedure. If you can do the assembly in discrete steps you may be able to use Titebond 3 if desired.

[John TenEyck]

Epoxy, Gorilla glue, or TB III and pin the joints with dowels. Epoxy and GG are more rigid but all work well when there's enough glue area.

John

[Frank Pratt]

There’s another glue option for outdoor wood projects that’s not often talked about. Silicon caulk and polyurethane caulking. I discovered it from my roofing days doing repairs. Polyurethanes bond on a clean surface is brutal to remove wood, metal ,brick stucco, bricks.
Silicon is pretty tough too.
Good Luck

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

[Michael Burnside]

Hi, how can you drawbore something after assembly?

Regards, Rod

Semantics. I meant as a last step of assembly and when driving in the dowel...seems we're splitting hairs a bit no? Technically just using a dowel in this circumstance, after assembly, is arguably sufficient if necessary at all.

[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? :rolleyes:

[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? :rolleyes:

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.

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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

[Rod Sheridan]

If it didn’t have glue the tenons would slide out of the mortise, that’s why doors and gates have glue in the mortise.

The tenons are slip fits in the mortises

Regards, Rod

[Andrew Hughes]

It could also be a testament to your skill to cut accurate tight fitting joinery. Comparing a door to a stationary object it’s a bit of a stretch.:rolleyes:
I thought of something I would like to share. If you ever buy a socket chisel and the handle falls off easily spray some aqua net hair spray on the wooden part and it will hold.
I don’t mind these discussions because there’s a lot of teachings that spill out of content creators that’s crap.
Definitely not taking about you Rod your advice and opinions I do agree with mostly. But still learning myself.
I do try to share my own lived experience almost never point to someone’s article or video.
Good Luck

[Melvin Feng]

I would personally also consider a polyurethane construction adhesive that you would apply with a caulking gun

[Mike Henderson]

I've used TiteBond III outdoors with fine results. But to echo Andrew, make sure you seal the ends of the pieces where you have tenons. If you don't, water gets in that crack and wicks up into the wood, under the finish and makes the final product look bad. That's true for any glue, not just TB III.

Mike

[Mike Ontko]

I feel like I've just been tapping on the proverbial hornet's nest with this one. Thanks all, for your responses. Your experiences, offered insights, and respectful banter are all part of the reason why I keep coming back to the Sawmill Creek community.

Incidentally, I glued up the blanks for the gate frame over the weekend (I want a 2-1/2" thickness for the finished gate), deciding to go with Gorilla. I've got a reasonable supply of Total Boat with the slow hardener, but didn't want to hassle with the potential mess (though polyurethane glue can be messy enough when it foams up). The cedar was freshly face-planed before the glue-up so, I didn't think a wipe down with acetone would be necessary before applying the glue. In following the manufacturer's recommendations (and my own past experience) I did, however, use a fine spray of water on one side then wiped down with a rag before mating and then clamping the pieces together. I'll do the M&T joinery for these four pieces first before creating remaining parts for the lattice.

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