Polyester resin for bent lamination?

[Jamie Buxton]

For many years I used urea formaldehyde (Unibond 800) for bent lamination. I became concerned about formaldehyde exposure, and switched to epoxy. It does a good job, but is a lot more expensive than the Unibond -- $100/gallon vs $40/gallon. I've been wondering about using polyester resin instead. Polyester is the dominant resin used in autobody work. For instance, Bondo is polyester. 3M's polyester resin is sold with fiberglass cloth in many car repair stores, and even at Home Depot. An attractive aspect is that it costs $40 per gallon. Does anybody have experience with it for woodwork?

[Howard Acheson]

Polyester's adhesive qualities are somewhat less than epoxy or UF. However, they may be more than satisfactory for what you want to do.

[Frank Drew]

Jamie,

I've never used polyester resin glue, just Weldwood Plastic Resin Glue, which is a ureaformaldehyde similar to Unibond, I guess.

What are the working characteristics of polyester resin? Open working time, etc.? What I like about Weldwood's glue is the longish open time, thin glue line and hard set when cured (no cold creep).

[Alan Schwabacher]

Polyester resin used to be standard for woodstrip/fiberglass canoe construction before the price of the wood went up enough that the greater cost of epoxy became inconsequential. The problem with polyester was that it did not stick to the wood as well, and delamination of the glass from the wood was much more common than with epoxy. That could be a concern if you wanted it to glue wood.

You can adjust the rate of cure of the polyester resin by varying the amount of initiator you add. (This is VERY different from epoxy where varying the amount of hardener will either prevent cure, or severely diminish the properties of the cured epoxy.) Breathing the styrene fumes from polyester resin is worse than epoxy.

[Tom McMahon]

In the 70's and 80's I use lots of polyester resin to build sculpture, We bought it in 55 gallon drums. In the process I would glue plywood into armatures with the resin. I don't think most people could tell the difference between it and epoxy. You need to be careful when catalyzing it too much catalyst and it will get really hot with lots of smoke. Guess how I know.

[Thomas S Stockton]

These guys make a low formaldehyde glue that is similar to plastic resin www.pro-glue.com/ I know people who use it for veneering and like it. I use their veneer softner and it is good stuff.
Tom

[John TenEyck]

The smell from polyester resin is way more offensive to me than that for Weldwood Plastic Resin glue, and hangs around for hours and hours. The only time I really notice any smell coming off Weldwood is during mixing with water, so I mix it outside. When I bring it in after mixing I can't notice much of any smell. It could be that I'm just fooling myself, but for what little I use (maybe one 5 lb pail/year) this seems safe enough to me.

[Larry Edgerton]

Not sure if it work for you but I did a lot of large exterior laminations for round Gazebos using redwood and Resorcinal [spelling?] glue. There have been no failures in about 25 year, but these are victorian so they are painted. Resorcinal leaves a dark line. Its non-toxic once it is mixed, the dust in the dry part is walnut and an irritant, it cleans up with water, and it works well when cured. But there are those dark lines......

[Jamie Buxton]

Thank you all. Alan and Howard have the answer for me: epoxy sticks to wood better than polyester. So I'll stick to epoxy.