Isocyanates - finish types

Forgot to make my original point...

David Weaver

...it seems like the isocyanates are in just about everything that's two part and really hard (like 2k poly types in a can).

Anything iso-free is spotty in terms of performance in reviews, and sold to larger users, anyway (like automotive).

So, I'm back to square one (which is usable), that being painting a guitar, then transition coat of clear shellac and target WB crosslinked over the paint.

The super hard commercial permanent finishes don't appear to be appropriate at all in anything other than commercial environments (and I sure wouldn't want to spray them for a living, no matter the personal safety clothing/equipment)

Re: Forgot to make my original point...

AlanWS

Isocyanates can be toxic because they are quite reactive. (The horrific accident at Bhopal involved an isocyanate.) They react with alcohols to make urethanes -- polyurethane means a molecule with many urethane linkages made in that way. The reason to have the isocyanate itself present is to make such linkages (and others) after the finish has spread, allowing it to be converted to a structure that no longer will dissolve, and that can be stronger. In this use it is generally a crosslinker.

"Silane ester" is a functional group more frequently found in things like bathtub caulk. In this form it is stored protected from water, but on exposure to water or humid air it reacts to ultimately form silicones, that is substances with silicon atoms linked by oxygen, and bearing carbon substituents. (Silicon is the element, silicone is the structure. They are different as carbon is from wood, though I usually try hard to not point that out.) Acetic acid can form as a side product during cure, which is why some of these smell like vinegar as they cure. While silicones are usually soft and rubbery, these linkages can be used to modify polymers in a way that hard polymers could result, with crosslinkers of lower toxicity than isocyanates. I would still not want to breathe them.

I understand you want to spray, and with appropriate ventilation these may be fine. I have used System Three WR-LPU, a water based clear varnish that is very durable. (I assume the crosslinker is a diisocyanate.) I used it on canoes so my standards for a smooth finish may not meet your requirements, but found that when applied in the hot of a summer day it dried quickly. But applied at dusk on a humid summer day it self-leveled to give a beautifully smooth surface even after brushing or rolling on: if you control temperature and humidity, you may not need to spray. It's the most durable marine varnish I've used.

Re: Forgot to make my original point...

David Weaver

Thanks, Alan - I do spray with an OV mask, which seems to be enough for something like the crosslinker in target, but not so much for isocyanates from what I've learned in the last day or two.

i don't need the finish to level or lay out perfectly, so the system 3 finish you mention may be fine. It's typical to lay on top coats for instruments, and then wetsand/buff them back to a more glassy finish. Something that will look similar to automotive clear coat and be tough over automotive type paint (like the original fender guitars, though for obvious reasons, those aged) is my goal. wiping or brushing is OK if that's the appropriate way to deliver the finish.

Outdoor application is tolerable if "open bug time" isn't too long.

Why not use auto paint?

Re: Isocyanates - finish types

Dick Coers

Did they change solvent based conversion varnish catalyst? I thought it was an acid base? That was when I was using Sherwin Williams quite a few years ago. I don't see the big advantage of water based, it still has the toxicity in it. Despite that benign image of water based.

Re: Isocyanates - finish types

David Weaver

I think some water based finishes like target are far more benign, but then others like the enduro 2 part finish that has a good reputation is isocyanate.

I've had good luck with crosslinked target and have never pushed it to see how scratch resistant it is. There's a gigantic difference between it with and without crosslinker.

The enduro finishes that are toxic appear to have some comment on them about being for professional users.

Not sure about conversion varnishes, but if bill is spraying them, I'm assuming they don't have isocyanates in them.

The initial draw for me in all of this is the fabulous performance of the spraymax 2k can product. Only spraying a guitar, i could buy one can for $18, build a finish on the guitar, buff it back and be done. Throw away the can, no clean up, etc.

On bigger projects, the cans would become a problem, but I already either wipe/brush/polish with shellac on those or shellac seal (for color) and then spray clear target WB over that. The sale of that 2k can stuff doesn't adequately warn of its dangers as I'd been warned either in comments or in forums and did the spraying outside of the garage and with a well-fitting OV mask, but it sounds like that's minimalist effort for it.

My regular spray and polish/brush options are OK, and they look like they're the appropriate options unless i want to go up in toxicity or use more spray equipment (and have to clean it).

Re: Isocyanates - finish types

Larry Clinton At Frankfort, (Central) Indiana

Unfortunately I doubt you will find any substitute for isocyanates that will have near the same properties. My experience is about 15 years old so I could be wrong!

However I worked as an Engineer at a fairly large facility and one of our product lines required that we coat (dip coat) an assembled printed circuit board to protect it from moisture during temperature cycling etc. We had a product containing Isocyanates that met all the requirements, but knew of the dangers so spent several weeks investigating / testing many different products - regardless of cost or application issues!

We also had our research lab (think tank) work on the problem.

End result was we found zero products that would meet the requirements and I installed a completely isolated room with separate heating / air conditioning that had a very high air exchange rate and the operator was provided with and required to wear the best protective gear available.

Thanks, Larry...

David Weaver

..that's kind of where I ended up with my nutty trail around various finishes yesterday.

I'm hamstrung spraying inside to just waterbased (and just target type stuff that's relatively benign), so most people in my case would choose a different route with guitars (nitro lacquer, and I probably would do that, too, if I didn't have a spouse. Especially a spouse who will make comments like (half hour ago) - that (johnson's paste wax) has an extremely strong smell and you shouldn't be using it in this house.

I read further about isocyanates and found an interesting comment in california's literature of all places. It mentioned that the toluene diisocyanate had proven to cause cancer in animals but there's no proof for other types so the primary objective seemed to be aimed at keeping people isolated from them for the *chance* of that, but more so the irritant properties and extreme sensitization that people can have.

It didn't say exactly that, but that's what they were implying. I think I may try spraying the cans of spraymax outside while wearing a respirator and glasses. It's something I'll probably only do 3 times, but it doesn't appear any other finish is going to offer a super hard bright tough automotive type finish at home.

I forgot to answer to one of the questions above about "why not just get car paint?", and I think the answer to that is two-fold: there are canned automotive sprays offered to hobbyists, but they're just one part clear coat and probably don't offer anything in this case above the options I already have. I believe most of the well-regarded auto two-part paints are not iso-free, but the spray situation for a commercial painter is with a positive air supply, in an isolated booth with exhaust leading away from the building and not being mixed back in with individuals.

After going in all of these circles, now I know what it is that the painters are protecting themselves from. It's been an interesting short learning burst and I appreciate that you and Bill are here with expert opinions far above and beyond those on the guitar boards where folks have responses like "i've painted for guitars with spraymax cans in my garage and having the door open is a no-go, but it's in my garage, so no problem".