Veneer glue problem

[David Kenagy]

This week at a class on veneering projects the instructor said Unibond 800 (a catalytic glue from Vacuum Pressing Systems) was reformulated a couple years ago. He said he never uses it any more, because of a problem with dark blotches. He showed me a panel with dozens of dark blotches. They appeared more than 6 months after it was completed. (Everybody’s worst nightmare)

He’s no amateur. The panel was gorgeous until the blotches appeared. He sent it to a chemist at Franklin (makers of a competitor, Titebond) who confirmed the problem is the glue. But it’s not the bleed-through that everybody gets (rapidly) with open grain veneers.

Is this problem widely seen? Is X-press glue also a problem? I really don’t want to switch to a glue that water or heat will affect.

[Kevin Jenness]

Unibond 800 was reformulated about 10 years ago. There have been some problems reported with chemical staining (blotches) of light colored veneer due to incomplete mixing of the acid catalyst crystals during catalyzation. The cure seems to be to mix the resin and catalyst with a drill paddle, let the mix sit for a few minutes and mix thoroughly again. Using the blocker to prevent bleedthrough may help as well, I have never had this problem but it does make me a bit leary of this product. I have not seen reports of similar problems with powdered plastic resin glue. I usually use a rigid pva except when I need the working time, moisture resistance and extra rigidity of urea formaldehyde or epoxy.

[John TenEyck]

I haven't had that problem with Unibond 800. I don't use a power mixer, but I mix thoroughly, let it sit for 5 - 10 minutes, then remix again. Oh yeah, I only use shop sawn veneer so maybe that greatly reduces any chance of that type of problem. I never get bleed through except though holes, cracks, etc.

Forget Weldwood Plastic Resin Glue; it's no longer available.

John

[Mel Fulks]

The formaldehyde assured glue consistency and thorough even mix. So my guess is that the new stuff needs some formaldehyde.
These days I read the Twinkie label to make sure they haven’t replaced the sugar with some something “more nutritious “.

[Kevin Jenness]

The formaldehyde assured glue consistency and thorough even mix. So my guess is that the new stuff needs some formaldehyde.
These days I read the Twinkie label to make sure they haven’t replaced the sugar with some something “more nutritious “.

Unibond 800 is a urea formaldhyde adhesive.

Powdered plastic resin (ppr, uf) glue is available from various suppliers like Veneer Systems and Veneer Supplies.

[Mel Fulks]

Kevin , thanks. I’m retired now, remember when it was unavailable for a while. The supplier we used then said US gov. wanted it gone.
I’m astounded by the current cost, but might have to use it for something.

Mel

[Jamie Buxton]

I gave up urea-formaldehyde glue at least ten years ago because of the formaldehyde exposure. I've used epoxy ever since -- West Systems 105. It works well.

[John TenEyck]

I gave up urea-formaldehyde glue at least ten years ago because of the formaldehyde exposure. I've used epoxy ever since -- West Systems 105. It works well.

Not without its own risks: https://www.westsystem.com/safety/he...sure-to-epoxy/

John

[Mark Rainey]

The only time I used Unibond 800 I used commercial cherry veneer ( 1/32" ). I think I applied too much. I did have terrible bleed through and had to apply another layer of veneer over that using hot hide glue. What a pain.