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I have 4 guitars on the go that are running behind. My spraying is done in the doorway of my garage, so no RH control. I usually spray at this time of year, not sure what the RH is but have not had any problems. I may be a month behind and am worrying a bit about a higher RH. I'm wondering what is the highest RH at which folks have had spraying with no blushing? Either with or without retarder.
Tom

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A person who has never made a mistake has never made anything!!!

50 - 60 % no big deal add some retarder to the nitro, have a cup of slow evaporating premium thinner handy, spray a mist after the coating begins to set up that will allow any moisture to escape -- actually blush remover is really a slow evaporating solvent.

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Ken Cierp

http://www.kennethmichaelguitars.com/

^^^ What he said. ^^^

I used to be real picky, and not shoot when the humidity was over 50%, but when work piles up...
Work smarter, not harder.

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

My limited experience suggests 60% is max, although where we are not concerned about a slower-hardening. softer film (primarily repair work, where only a couple coats are needed), we have added retarder to spray above that.

HVLP turbine is a big help when spraying at higher RH and lower temperatures - during the week I spent on my 'finishing intensive' spraying everything and anything, it was interesting to see how five different test mules (old classical bodies/guitars from a defunct shop in Baltimore) behaved with good compressor conversion and high pressure guns and the Fuji turbine system...at the same RH and temp I could spray 85% lacquer/15 thinner from the turbine, the HVLP conversion gun would pick up minor blush, and the high pressure gun would produce major blush. Adding a little retarder resulted in almost blush-free application, and more retarder allowed me to get blush free finishes up to least 66% RH and 58 degrees F air temperature (max RH for the period I could spray), but the film was noticeably softer than an unretarded finish after the 10 days in the drying box.

I am looking forward to trying out General Finishes EnduroVar in a week or so - a former student that is working in Mr. Greven's shop was kind enough to bring his latest Stauffer-style travel guitar over and the boss was impressed with both the guitar and the finish material. I forgot to ask what maximum RH is for spraying waterbournes, but with Mr. Greven in Portland, OR and producing 70 guitars a year, I have to guess it's relatively insensitive to high RH.

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A constellation only takes shape when one maps the whole.
- Beth Brower

Thanks guys............feeling better as I use a HVLP turbine. Ken, not sure what you are saying. Do you use 2 spray guns ? And are the retarder and blush remover one and the same?
Tom
PS Guess your saying have 2 cups for the same gun......??

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A person who has never made a mistake has never made anything!!!

Most lacquer retarders and blush removers use butyl cellosolve as a major ingredient. You can mix it in your lacquer as retarder or spray it as needed on the surface during or after blushing has occurred. Mohawk makes "no blush" and "no blush + retarder" in an aerosol can. If you see the finish starting to blush a light mist over the surface is usually all that is needed. They can sometimes be used to remove blushing on dry finishes (they redissolve the surface).

Its been a long while since I sprayed nitro with compressed air. But yes I had a separate gun with just the thinner, I did not mix it with retarder (I could have 75% - 25% that's blush remover) I mixed retarder right in with the nitro and the thinner gun was filled with a premium slow evaporation formula thinner I bought mine from Sherwin Williams.

Two cups would work great too. I always ran plenty of thinner through the gun while cleaning up so a cup of thinner is needed anyway --- clean up! the part I really really really hate. The water clean up for our little HVLP system used for Endro Var is also a pain but not as bad as nitro.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Conversion gun, nitro, 60% RH limit for me.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Many years ago I sprayed a few coats while it was raining outside. My exhaust fan was pulling in the 100% RH air. No blushing and no problems. One can easily spray in very humid conditions by using what they call a slow thinner.

When I am spraying on cold/ humid days in the garage I keep the guitar inside until just ready to spray. I have a cheap dual halogen work light/ tripod. The 500 watt bulbs that came with it were junk, replaced them with 300 watts. As I mix the lacquer I have the light shining on the gun from about four feet distance, trying to keep things warm and dry. When spraying the guitar I keep the lights on it, again at four or five feet distance. Too close and you can make pinholes.
This system lets me go probably fifteen degrees colder and a small amount more humid than I would dare do otherwise.

I've sprayed in very humid conditions before and the only time I got blushing was when there was fog in the air. It was dumb, I knew it, lesson learned. I think 60% is a reasonable best practice but you can push it a bit closer to the dew point.