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So I got myself some gloss top coat and some epoxy from solarez to try. With both products I encountered a strange thing. If left on as a thick coat, it cured normally no problem. But whenever I tried to make it a very thin coat, it would not cure. I tried to use it as a normal epoxy pore-fill (excess squeegied off) but it wouldn't cure, evenafter 2 1/2 hrs in the sun. A dime thickness glob placed beside it cured in one minute like it's supposed to. Same thing with the gloss polyester.
Could someone with a bit of leftovers try to repeat this phenomenon?
Thanks
Also, done on MH, RW, and MDF...

Here's my theory, and it's nothing more than that. Any resin that soaks into the fibers of the wood may be obscured from sunlight, and thus unable to cure properly. Same may hold true for resin in the pores if light is unable to fully reach them. That may affect the cure for the entire coat if it is thin enough. The thicker the coat, the more likely the upper layer of the resin will cure completely, although the resin down in the pores and wood fibers may still be soft.

BTW - when you say epoxy, are you talking about the vinyl ester "epoxy" they offer, or the ZeroVOC product? I have some of the polyester (Solarez) and the vinyl ester, which I have been playing around with. I have had inconsistent results and don't fully understand why. I have actually been able to get both the polyester and the vinyl ester to fully cure on bare rosewood at times, but not always. I need to do more testing before I have any confidence in my results, though...my sample size is very small so far.

Glad to see others are playing with this stuff. I have been looking into acquiring a barrier coat product of some kind but they seem to only come in very large (expensive) quantities. I don't know whether it would be possible to split it with several users, but it's a thought.

Good question...
I ordered vinyl ester but got ZeroVoc.
Tonight I will add MEK and see if it will cure. I had no trouble getting either product to cure on RW in a thick coat, just thin that is a problem. Hopefully enough mucking about will yield a solution.
Can you try to lay down a very thin layer, squeegee of the excess as if it were zpoxy, and see if you can cure it? And post results, of course...
I'd like to know if it's something I'm doing weird...

Will do. I don't know whether I'll have a chance to get to it before the weekend, though. I've been trying to do my tests around midday when the sun if fairly high. Late in the day, after I get home from work, the cure seems to take longer, and I want to remove that variable from the equation. I will do it asap and report back with my results.

BTW, are you using any sealer or barrier coat between the rosewood and the resin? If so, what are you using?

I am not familiar with all of the plastics, but there is something relevant regarding standard plastic resins, such as used for fiberglass or Bondo. These do not set properly if exposed to oxygen. The normal practice is to mist the surface with liquid wax after casting or applying the resin, unless the product has liquid wax in it. Some manufacturers sell bulk product without the wax incorporated, because the user is supposed to know about this and apply his own surface wax. When you buy a pint or quart of fiberglass resin in the auto store, I think it has liquid wax in it. You need to sand between layers of fiberglass to remove the wax so that the next layer will adhere. If you buy resin kits in the hobby store to make paper weights, those have liquid wax mixed in at the factory, so you would never experience the lack of setting. The wax floats to the exposed top of the casting.

In your instance, it may be that the oxygen only inhibits the surface thin film of resin. With the thick glob, the surface may be tacky forever, but the majority of the glob may set. Thinner applications would have too much exposure to oxygen.

So, maybe check with the manufacturer to see if you are using a product that needs to have surface wax applied, which personally I would try to avoid on a guitar.

Good thought. I do know the Solarez polyester resin contains a "surfacing agent" (wax) to shield it from oxygen and allow it to harden completely, similar to what is called "sanding resin" in surfboard manufacturing terminology. But I suspect the vinyl ester does not contain the surfacing agent as it tends to cure with a slight tackiness on the surface. That works fine for my purposes as I would use it as a barrier coat over which I would apply the polyester. In theory, the vinyl ester should not be affected by the oils in rosewood the way polyester can be.

For what it's worth, I just today experienced the same phenomenon with the top coat product from cureuv.com. I decided to try a brush on, wipe off application to see if I could put on a super thin, nib free coat that I could just lightly sand prior to a second coat. Even after hitting it three times with the uv light, the stuff did not cure. Took a long time to get if off, but when I did and put on a thicker coat, it cured fine. Weird.

Pat

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Those that make things happen,
those that watch things happen,
and those that wondered what happened.

Strange indeed.
I tried adding the MEK as suggested on the bottle, and that did not cure either.
I'll have to get in touch with Gary to ask some questions...

Like Charlie mentioned you probably need a barrier coat. I use ML Campbell Exotic Woods sealer. Gary (at Solarez) recommend vinyl ester, but I didn't get the results I wanted with it. (it wouldn't cure on Rosewood without a barrier coat). If you're experimenting try some zinsser seal coat. I'm not sure if it should work, but it might.

Pat, were your problems on oily woods, like Rosewood? Doesn't Cure UV offer a UV cured barrier coat for oily woods?

FWIW, I use the sealer on all woods, not just oily woods.

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A loooooong time ago, When I was a young, I worked for a company that manufactured cast polyester panels. These were catalyzed with MEKP. During the curing process quite a bit of heat was generated. No heat no cure. It could be, and I am just guessing, that the very thin film does not generate enough heat to cure.

Cecil

I've laid up a couple of test panels with West epoxy as porefill on RW. We'll see if that helps later today...

I just did the same thing, but on some cheap "mahogany" ply from Home Depot. I also just did the testing I mentioned earlier in the week. I put a very thin coat of the polyester on some freshly sanded spruce...just smeared it on and then wiped it off with a paper towel to get as thin a coat as possible. A few minutes in the sum and it cured just fine. Then I did the same on a freshly sanded piece of rosewood (EIR) and it cured just fine as well. Hmmm...

I'm going to keep playing with this stuff and see if I can achieve some predictability. And as I mentioned above, I've got some test panels going with epoxy pore fill. I'm going to try the vinyl ester as a barrier coat between the epoxy and the polyester, possibly with a coat of shellac between the epoxy and vinyl ester. I'll report back