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?

Garden Gate.png Garden Gate_joinery.png

[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

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.