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Epoxy vs. Weldwood


Konrad in Lincoln
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As some of you old-schoolers know, my Vacationer is now 6 years old. I almost exlusively used Weldwood to make the boat.

There are a few areas where it seems epoxy may have been a better choice. Secifically, the rubrails are wanting to separate from the hull. That glue joint has separated in a few places around the perimeter of the boat. And no, it's not from dockside abuse.

My suspicion is that epoxy has a greater modulus of elasticity than Weldwood. Which doesn't matter, unless your boat is going to see wide climate swings like mine has recently. Up until a year ago, the boat lived in a semi-heated shop all winter. But we've moved and now it lives under a tarp in the drive way.

I think the temp changes and humidity swings have played hell with the weldwood bond since it's moved outdoors. I think that stuff is very brittle once it's cured. Keep in mind that here in Nebraska, we regularly experience a temp differential of about 120 degrees in any 12 month period. It was 104 three weeks ago, and in 5 months it'll be 15 below.

It's not like the boat is coming apart at the seams, but this all started this last year. Just some thoughts to pass along.

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My two cents,

I built a wood framed, PVC covered kayak about 15 years ago in Cleveland OH. I then moved to Hell, aka Roll AZ, with huge extremes of hot and cold and humidity, due to flood irrigation (boy was that fun :shock: ) It was always been under cover but exposed to the outside temperatures. I've bashed against rock hard enough to have to splice a stringer but I've never had any of the weldwood come loose.

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Konrad, as an old schooler--i remember many of your posts describing some pretty hellacious sail adventures youve had. that may be why your joints are showing more stress than other sailors who are not insane. :lol:

that being said, i used epoxy on all joints only because my boat would be moored instead of trailered. most trailer-sailors seem to be happy with weldwood.

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Weldwood Plastic Resin is pretty stiff stuff Konrad. You're correct in that epoxy's modulus of elasticity is very good, especially some formulations used in specific applications like CPES. I don't think this is the issue with your bonding failures.

Weldwood has been used extensively for many generations of builders, though has been replaced to a great extent with newer adhesives. It's cured color, grip on raw wood, ease of use and cost contribute to it's steadiness and continued use in the industry. Bonding issues usually can be traced back to insufficient clamping pressure, less then ideal mating surfaces, moisture penetration into the glue line and dirty or contaminated bonding surfaces. Enough clamping pressure is the one I see a lot, usually coupled with less then well fitting joints, both are mandatory for good results. Good coatings (paint, varnish, etc.) will keep the moisture content to reasonable levels. Urea-formaldehyde adhesives (Weldwood) create a bond stronger then the fibers of the wood, so cycling expansion/contraction loads from temperature changes should tear out the wood fiber, not give at the glue line.

Can you see the glue line with a clean (reasonably so) separation from the bonded surfaces? If this is the case it was likely prep not being as good as necessary (clamp pressure, matched joining surfaces, clean bonding area or moisture on the glue line). If you see wood fibers attached to the glue, then it wasn't the glue, but something else. Weldwood is a type II (I think) rated adhesive which is only water resistant and should be well coated if used on the weather side of any boat part.

Personally I use the stuff all the time (I'm old, I guess) though limit it's application to interior uses.

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104473106.jpg

Even with good, tight joinery and high clamping pressure....resin glue requires protection.

It's a bit brittle.....in analyzing failures, I often surmise that the glue was sufficiently waterproof, it was the increased wood movement caused by degraded coatings that did the joint in.

But it remains my glue of choice for interior work.....it's cheap....it colors and sands better than anything else yet...has gobs of open time....and most importantly, it glues over well with epoxy in repairs.

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All good points.

I do like its color and up until this year I was happy with its performance.

The clamping issue.. I didn't own $200 worth of clamps at the time I built the boat (and I still don't) so I relied on glue-and-screw method. It's very possible this was part of the problem.

But I still think that the recent exposure to wide seasonal changes was the catalyst that pushed the joint beyond its limit. Otherwise this would have shown up several years sooner, I think.

I'm not talking about catastrophic failure of any part of the boat, just some annoying age starting to show up. I'll snap a photo in a day or two.

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