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I'm spraying Behlen vinyl sealer today. Shop humidity is hovering around 50% and outside is 58%. I vent the booth by drawing in outside air. Both my IRW and Mahogany are blushing. I have some Jet blush eraser on hand so the problem is taken care of, but I had hoped to be on a spray schedule this weekend and coming week. I've sprayed many years and this is the first time I've ever had any blushing. Anyone have an idea as to how much humidity (percentage wise) is too high to spray? Up until now I would have considered the current weather (clear, 70's) to be ideal. I may have to buy some retarder... more delays.

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It will probably be alright.

Some times the lacquer "thinner" can be a problem -- the better grades usually evaporate slower allowing time for the moisture to dissipate. I am pretty sure the blush remover is simply lacquer thinner with slow evaporation properties.

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Ken Cierp

http://www.kennethmichaelguitars.com/

The blush eraser is an aerosol product, not a lacquer additive. I can't figure out why I am getting blushing under what seems to me to be adequate humidity.

Anyone know if paint store retarder is ok or should I go for Belehn brand and wait for shipping?

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It will probably be alright.

BTW the sealer is being sprayed right from the can as usual, no thinner added.

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It will probably be alright.

No its not an additive its simply a solvent formula or combination. Perhaps I did not make the point clear -- Blush Remover is slow evaporating solvent aerosol or other you spray on to soften the finish.

On the other point which could actually help explain your situation -- if you thin your coating with a "slow" (retarder) evaporating solvent it will take longer to dry thus letting the moisture escape. But since you are using cans it might be that the viscosity of the sealer has changed more solids less solvent left in the mix or a different batch from the maker if new can/s.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Thanks for the help Ken. This is a new can of sealer, just arrived from StewMac. It's going on too dry, even after I opened up the fluid nozzle to get more material out of the gun. Frustrating!

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It will probably be alright.

Gotta be a problem with the sealer. Humidity is even lower now, 44%, different gun, full wet coats. Still getting blush.

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It will probably be alright.

How about the temp, outside vs in. If your shop temp is at a lower level than outside and you are suddenly letting the two combine could
cause the problem. I'm sure you probably are aware of all of this stuff but apart from a bad batch humidity is usually the culprit. My first
reaction would be to warm the guitar before spraying or raise shop temp. Just a thought?
Ken

Thanks Ken, shop and outside temps are low 70's, humidity about 45%. I'm stumped. Going to let it set for two days and then sand back and spray some clear. Hopefully will be ok, if not it looks like I'll have to sand back to raw wood and start over, not knowing what went wrong. I'm not new to this, been spraying since the 80's and for the last three years in the current location with same equipment, lacquer sealer, etc.

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It will probably be alright.

Any chance you've got water in your airline?

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Jim Watts
http://jameswattsguitars.com

Cut-off for me is 60% RH. Busted hygrometer(s)??

Very wet coats=>more evaporation=>more cooling of the target=> higher risk of condensation on target=>blooming.

Thin panels have less heat capacity so cool more quickly. Warming the lacquer and/or the target can help. But it also seems that somethings else has changed (been changed) on you. Lacquer formulations (around here at least) seem to change without notice as cost/availability of components changes and regulations change. I wouldn't mind so much if they sold the stuff under a different name/number, then at least you'd know!

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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

You can thin the sealer (and lacquer) with a small amount of butyl cellosolve, which slows the evaporation of the mix and allows the water vapor to escape.
Depending on your fan set up, drawing outside air across the work can sometimes cause blushing

Rapid evaporation of the solvents in lacquer cools the surface of the instrument below the ambient temperature which causes condensation or blushing. That's why your beer can gets wet when you are outside on a humid day. The solvents in lacquer contain alcohols which are hygroscopic and draw in moisture. You can minimize blushing by warming the instrument and the spray can or gun several degrees above outside ambient temperature. It might not be enough on really humid days but it usually helps during conditions that you describe. Spray cans can be warmed in water and you can warm the guitar by carefully using a hair dryer.

Mike Franks
www.mjfranksguitars.com
www.facebook.com/mjfranksguitars

Thanks for all these tips and ideas. I do have a professional quality water trap just before my hose that leads to the booth, and I drain it and the compressor tank before each session. I have two digital hygrometers and a wet bulb dry bulb hygrometer so that's not the issue. I've never had to warm lacquer or the guitars before, but if that helps I'll try it. I'm not drawing outside air directly across the guitar, but I do rely on fresh air intake across the shop to vent the booth.

Butyl cellosolve... is that the same thing as retarder? I have Behkol, reducer, and thinner on hand but no retarder. My local Sherwin-williams has retarder, will any brand work or should I order some Behlen retarder since I'm spraying Behlen products? I've never had to deal with anything like this before, so sorry for all the questions.

BTW, the blush eraser I used helped a lot but there are a few areas that stayed lightly clouded. This is a very dark set of Rosewood so the cloudiness really shows badly. I am hoping they will sand out (this is sanding sealer after all) and that the clear coats will melt in and all will be well.

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It will probably be alright.

I had the same problem with Mohawk on two guitars (sprayed at the same time). Blush eraser didn't get it all out, guess it was too deep but it did sand out. My shop was at 45% and about 75 F. Only things I could figure is maybe I sprayed too wet and the make up air coming from the window (open about 1 1/2") about 10' away was too humid. I have a drier right before the spray gun hose but the booth exhaust pulls a fair amount of air.

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Steve Smith
"Music is what feelings sound like"

Butyl Cellosolve is often called and sold as "retarder". Many of the "blush erasers" are this compound in a spray can, but it comes as a liquid and can also be added to the lacquer before spraying. It does slow the initial flash off of the lacquer so you don't want to overdo it.
The blushing that remains may have been too deep for the blush remover to soften the sealer and allow the water to leave. If only slight blushing remains after sanding then the first coat of lacquer may burn in and eliminate it. If it doesn't you will have buried the cloudyness under a layer of lacquer. Alternately, you could spray it with blush remover after sanding to remove the last traces of blushing before top coating. If it doesn't eliminate it, I would sand back until the cloudyness was gone.

you don't exactly describe your spraying set up, but from what you've said it appears as if you have things correct...that being a moisture (and oil if needed) trap about 25' of hose from your compressor then the hose that goes to your gun...having a trap right at the compressor doesn't get it all...

there is nothing wrong with thinning your product a bit other than of course it will be a different thing to learn...e.g. it will run easier than perhaps you are used to...and I mean thin with a decent reducer not something from Hell Depot...as has been noted you can also simply add some retarder and that might solve your issues...be aware of the properties of any retarder you acquire...IT DOESN'T TAKE MUCH!!!! that being qualified when dealing with such small quantities of a product being added to another be mindful to mix very well...too much retarder will greatly increase the time for the lacquer to fully cure and harden.

your blushing sounds bad enough that I'd suggest you just bite the bullet and sand it off before you spend anymore time going further...

oh, and you can have a disposable moisture trap right at the gun

I believe the OP is in regard to "rattle can" application of sealer. Seems like a product formulation batch run issue to me, its drying way too fast. $.02

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Ken Cierp

http://www.kennethmichaelguitars.com/

the blush eraser is in a rattle can...he describes a water trap as part of his system later on in the thread...and compressor...etc.

Call Mohawk & ask to talk to Phil, the tech guy.

Sounds like a bad batch of sealer.

Here's a short thread also which may be helpful
viewtopic.php?f=10101&t=40958&hilit=retarder

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Hi Greg,
The Sherwin Williams retarder should work with Behlens, but test on scrap, as always suggested.

Add a touch of retarder. I buy mine from an autobody supplier. FWIW I spray year round and will spray up until 85% RH. It comes down to knowing your equipment and materials and what ad-mix to use.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

The sealer I sprayed is from a quart can, not rattle can. The blush remover is aerosol.

My setup (which has worked fine for years) is an upright compressor with a vertical galvanized pipe run of several feet followed by a slightly back-sloped run of about 20 feet (as far as I can go in my small shop) followed by a vertical drop to the water trap and then a short section of hose at the booth. The hose is maybe 8 feet. Booth is exhausted using a fan that draws air across the open door of the shop, door leads to the interior of my house. I open upstairs windows for fresh air intake.

I've sprayed many times under much less ideal conditions with more temperature differential than yesterday and had no issues.

Thanks for the tips and links. I'll keep on this and see what I can find out. I can say that the sealer was drying ultra fast, almost as fast as I sprayed it. Much more problems controlling over-spray than usual. To repeat, I have quite a bit of experience with this equipment and know how to adjust air pressure, gun fluid, etc. Nothing seemed to work right with this session.

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It will probably be alright.

I'll call Phil at Mohawk tomorrow. I copied this from the link shared above:

"Only use the minimum amount of retarder required to inhibit premature skinning which traps volatiles. This looks like millions of pinpoint bubbles evenly spaced throughout the film.

Along with the mild blushing on flat surfaces, I am also seeing this on the edges of the Rosewood overlay on the peghead. Seems like premature drying based on this comment.

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It will probably be alright.

Of course you are correct -- Just the same I believe it is a product issue, its drying too fast which to me indicates the need for some retarder. At at any rate since it is a new can of coating I would try that before messing with any adjustments or equipment that has worked flawlessly for a very long time.

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Ken Cierp

http://www.kennethmichaelguitars.com/