Official Luthiers Forum!

With all the chatter about finishes lately, I have a serious question for our pro finishers.

Would you rather go in the booth multiple times to spray nitro or twice to spray cat polyurethane?

Realizing that neither are particularly good for a person’s health, One has to wonder what the lesser of evils is here?

Please advise
Dave

HI Dave,
In my opinion, you don't want to apply either of these finishes if you are having to choose which one is the worse for your health. Only apply these finishes if you can do so while suffering absolutely no harm to your health. If you are protected, then it doesn't matter how many times you are going into the spray booth. In other words, you ONLY want to use these finishes if you can apply them safely. Both are quite toxic !!!


BUT I do know what you are getting at here. I think the catalyzed urethane might be worse - with the isocyantes in the hardeners potentially life threatening for some individuals who might be sensitive to it. A lot of folks spray this stuff and throw caution to the wind -- and they are fine -- and some get cancer or get rushed to the ER. I'm not willing to take ANY risk !!! I've got a sufficient spray booth that captures all the overspray. I'm wearing a Tyvek spray suit, latex gloves, and a full face 3M respirator with fresh cartridges. Nothing gets on me while I spray. My shop smells bad for a day but when I enter it -- I'm decked out in the PPE.

I think the Urethane might be a bit easier to apply just because you don't have to shoot as many coats. But then again, there's a bit more sanding involved because you must have mechanical adhesion rather than chemical adhesion between coats. But I've found the sanding fairly painless. I also think the urethane is a bit better or the environment -- the chemicals catalyze and therefore, lose their toxicity. You do have the solvent carrier but urethane is a fairly high solids paint. However, with the amount of finish we apply -- environmental concern isn't that high on the list.

I think the main reason lacquer can be easier to apply is that you never have to worry about witness lines - it's easy to spray and relatively easy to keep thin. It's super easy to level and buff. Urethane is a bit more work in some regards but also easier in others.


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One consideration is that VOC's are the things that linger in your shop and nitro has got more of those. Bar none, the worst thing about the urethane for me is the MEK smell -- it lingers but is mostly gone by the next day. If it helps any, I believe urethane is easier for me to spray safely. I don't believe I could apply lacquer safely in my current shop setting.

It's not about toxicity. It's about following all the safety rules for shooting whatever finish you choose. Be smart, and live.

_________________
"Act your age, not your shoe size" - Prince

From what I have read, I think catalyzed finishes are more dangerous during mixing and spraying, but they become relatively harmless in a few hours, whereas nitro stays dangerous for weeks. I can take extreme precautions for a few hours of mixing and spraying, but I can’t take extreme precautions for weeks at a time. So, in my view, catalyzed wins the safety contest (despite being more dangerous).

+1 to what Don said. A whiff of any of these things isn't going to kill you. Splashing it on your face/eyes or ingesting is a different matter altogether -- but just getting a little bit on you isn't the worst thing in the world so long as it happens very occasionally. The biggest issue with spraying is that you are atomizing this stuff and without proper ventilation -- it goes EVERYWHERE. So if you protect yourself, have proper a spray booth that effectively moves the right amount of air -- then you can spray either of these without problem. If you can safely deal with lacquer offgassing -- then both options are on the table for you. Personally, I wanted to see if I can get the tone I seek with urethane -- if so, I believe it is a superior finish to lacquer unless you build for the traditional crowd.

Feel free to give me a call if you undertake the urethane. I'm more than happy to help !!!

--
Simon Fay (contact information is on my website)

One of the best painters I know worked for LearJet for 35 years. He said the deadliest stuff he ever worked with was Imron.

_________________
"Act your age, not your shoe size" - Prince

I sprayed nitro once. Never again!!

With Nitro, when you can smell it through your respirator it is time to change your cartridges. With 2K PU if you can smell it , it is already too late. To use cat polys it is recommended (required) to have a fresh air supplied respirator (preferably a full hood to also protect your eyes).
Like epoxies, polyurethane is a sensitizer so avoiding even skin contact is recommended. Some people have acute reactions to it after becoming sensitized.
Nitro destroys your organs a bit more insidiously, like over consumption of alcohol (in combination, a one two punch ).
With Nitro and cat poly it is the adjunct materials that seem to do the most harm - solvents, thinners. and catalysts.
We picks our poison and takes our chances.
Brushing a waterborne finish is the safest bet, but the limited contact we have finishing guitars nitro and poly is probably not going to kill us (right away )

That's why I like stuff like Watco or TruOil....

_________________
"Act your age, not your shoe size" - Prince

Thanks for,the responses. Good stuff to think about.
Like Toonces, I’m searching for an alternative to nitro.

I would French Polish EVERYTHING if people wanted that. But it is so fragile on steel string guitars.

My nitro technique is just fine. I lay down a nice thin layer, but it’s so time consuming.

This is why I tell people that once I have a closed box in the white, I’m only half done.

Are you saying two coats of urethane is enough?

all finishes can be toxic use a proper spray area
Nitro is fine with the proper protection

I agree change your cartridges often

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Hi Ed,
I don't think 2 coats would be enough -- it's enough if you "base" is already perfect. Here's my basic schedule:

2 Light Isolante Sealer Coats
Pore Fill
Sand Back (exposing wood in various places)
1 Sealer Coat
3 Urethane Coats
Sand Back Perfectly Level (leaving about 1-2 mils)
2 Coats on Top, 3 More on Back
Wait 2 Weeks and Level/Buff

If you went with satin - you could save a ton of time. But a perfect high-gloss is a lot of work regardless of nitro or urethane. Urethane is nice because you don't have to shoot a ton of coats and because it dries very quickly.

Question was to OP in regards to only entering the booth twice for urethane...

You being a Doc and all, it would be entertaining seeing people in future generations trying to decipher what you wrote inside on the top!

Nothing wrong with nitro, wear the gear,

That's only a small part of the problem.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Maybe doing finishing is not for you.

_________________
"Act your age, not your shoe size" - Prince

No, my issue is only with nitro. I've sprayed about 5 instruments with it and it was easy from the get go. They always come out great and I will most likely fall back to this when I can do it outside and let the guitar gas off outside as well. There's about a 6 month window for that up here in the northeast. I've sprayed in the winter outside but don't have any desire to do that again so I'm going down the waterborne path with a brush, no annoying compressor.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

In my opinion no more than nitro.

The difference is 2k urethane makes you a bit sick if you spray it without any protection. A 3M mask is enough to stave off any symptoms from it (I mean the cartridge stuff, not the N95 medical mask for COVID).

Nitro doesn't really cause sickness apart from some headaches if you sprayed it without protection but neither is too good for your health in the long run.

But in Taiwan I see everyone spray the 2K stuff (I got a few auto modification shops nearby) with little more than a N95 mask and they seem fine.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Yeah, there are no long term health effects from cyanide poisoning. Unbelievable.