Spotted Gum Exterior Lamination's

**sleake** · 11th October 2021, 01:52 PM

Hi Everyone.

I'm planning to face laminate 150 x 50 spotted gum boards (of which I have a bountiful supply for free) to build up some ~140 x ~140 posts for a small pergola/arbor. It is a very simple garden structure and although I would be frustrated if it fell apart, it wont be the end of the world, hence my aim to keep the costs down rather than stump up the $80 bucks/m or so for 150 x 150 posts.

They will be very exposed to the weather, and my glue options will obviously be critical to minimize headaches down the track of lamination's separating (disaster!).

Knowing spotty can be a little hit and miss to glue, and the outdoor application, I know I am asking a lot of whatever glue I use.

Ideally I hope to use titebond III - I have plenty of it, and have used it alot in the past, but not in such a long term exterior application. I like the idea of simply squeeze, roll and clamp, but hope that it is waterproof 'enough' and resistance to creep is enough to stop movement while the boards fight the elements for the next few decades.

Polyurethane, epoxy and rescortinol (spelling?) are other options, anybody think that these would be a better option? All have there merits and pitfalls, polyurethane can be a messy headache, epoxy needs mixing and rescortinol would be very hard to find I expect.

Would love to hear anyone's thoughts and opinions.

Thanks, Steve

**riverbuilder** · 11th October 2021, 04:08 PM

Epoxy is the only option worth doing. It will still be there when the timber has rotted away. Rough sand all surfaces to be joined and wipe them clean with acetone then use a notched scraper to get an even surface of glue, don’t over clamp.

**Eggman2** · 4th October 2022, 09:57 PM

Hi Sleake,

How did you go with this? I've got a similar project coming up. The temptation is to reach for the Titebond III. However like you, I've got concerns that it is the right product for a exterior lamination with spotted gum.

**Bushmiller** · 5th October 2022, 09:30 AM

Eggman2

I would go with Riverbuilder's suggestion and use epoxy. Something like this:

Epox-E-Glue the best Epoxy Glue (boatcraft.com.au

Epoxy is gap filling and should not be clamped hard as you would with Titebond 3, which is the main glue I use. Excessive clamping squeezes out the glue and results in poor adhesion.

Regards
Paul

**Mr Brush** · 5th October 2022, 01:24 PM

I'd go with one of the construction-grade polyurethane adhesives. Several outdoor items I assembled with this more than 10 years ago (including laminations) have survived rain and full sun with no degradation at all.

Forget about TBIII - definitely not up to the job for long term outdoor applications IMHO.

**Eggman2** · 6th October 2022, 09:47 AM

Thanks Mr Brush,

What are the advantages of polyurethane over epoxy?

**Mr Brush** · 6th October 2022, 09:59 AM

Apart from knowing first hand that it holds up well in outdoor applications long term, it allows for timber expansion/contraction over a wide temperature range a bit better than epoxy IMHO. I'm sure epoxy would work well too though.

I just found something that works for me, so I'm sticking (groan..) with it.

**Eggman2** · 8th October 2022, 10:00 PM

Thanks Mr Brush. Given that polyurethane foams when it cures. I assume that you would see a pale coloured glue line when doing a lamination.

**Mr Brush** · 9th October 2022, 08:11 AM

Strangely, not so much when it has finish on it. Barely perceptible. The same will apply for epoxy though - if you clamp up an epoxy joint as tight as you would PVA, you'll squeeze all the epoxy out and end up with a weak glue line.

**Eggman2** · 9th October 2022, 07:11 PM

Thanks Me Brush. So what is the general guidelines for clamping pressure with epoxy? Also when you were talking about industrial grade epoxy, do you have any recommendations on brands?

**GraemeCook** · 10th October 2022, 03:39 PM

Boat builders largely switched from resorcinal to epoxy glue about 50 years ago. It is had to imagine a more hostile environment than the marine one and epoxy has stood the test of time.

Riverbuilder's methodology is sound; I would use either acetone or MEK for the initial wipedown, then thicken the epoxy a little with mircrofibres and apply the epoxy while the acetone is still wet - this aids penetration. Clamp evenly but moderately.

Any of the brand names are good. I use WEST System and a local fibreglass shop's generic copy thereof. Avoid the discount brands - especially the "5-minute" ones.

The only glues that I use are PVA and epoxy - they work for me - and, in spite of Mr Brush's enthusiasm, have never felt the need to use polyurethane.

**Eggman2** · 12th October 2022, 09:19 AM

Thanks Graeme. Are you talking about using a normal clear epoxy resin or something like Boatcraft Epoxy-E-Glue?

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