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Humidity vs. Aerosol Nitro Lacquer

Discussion in 'Finely Finished' started by Frickensmith, Sep 16, 2019.

  1. Frickensmith

    Frickensmith TDPRI Member

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    I am wondering about humidity levels when spraying clear gloss coat aerosol nitro lacquer. I live in Illinois near Chicago where humidity levels usually hang out near 70%-75%. I am reading that you need to spray in low humidity levels to avoid "blushing", but how low is low enough?

    Today, for instance, it is in the mid 70's, and the humidity level is around 75%; is this ok to spray? I'm seeing posts that say anything under 80% is fine, others saying wait until it's at 50%. Low humidity levels are hard to come by around here.

    Some threads have recommended using thinners or other additives for spraying clear coats in humid climates, but since I am using an aerosol nitro lacquer I cannot add anything to aid this process. Is blushing really that easy to come about? Is it difficult to correct?

    I really want to get a nice finish, but I am impatient and would like to keep working if I can. Any advice you finishers could provide would be greatly appreciated.
     
  2. dan40

    dan40 Tele-Afflicted

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    I have sprayed rattle can nitro with the humidity in the 70's. The trick was to use very light coats. If I tried going too heavy in one pass, I would get some light blushing. I usually do three light passes per coat but with humidity that high, I had to back it down to one or two light passes per coat to avoid the blushing.
     
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  3. Frickensmith

    Frickensmith TDPRI Member

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    Thank you for your advice! When you ended up getting some blushing with the thicker coats, what did you do to remedy? Did you use any blushing retarders or anything? I will certainly follow your advice to spray in thin coats, but want to be prepared in case of a mistake.

    Hopefully others who have used rattle can nitros will chime in. I am purely a hobby guitar finisher (really more of a player who is getting more into building) and it doesn't appear to make sense for me to spend a ton of money on spraying equipment. The rattle cans make things easier on my budget.
     
  4. Freeman Keller

    Freeman Keller Friend of Leo's

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    Generally I just wait until the RH drops to the 50 percent range. I've got a lovely guitar that I sprayed some years ago and it blushed - I've tried blush eraser and it didn't work so I'm seriously contemplating stripping and refinishing.
     
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  5. dan40

    dan40 Tele-Afflicted

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    I used a bit of the Mohawk blush eraser in the aerosol can. Luckily I was very early in the process and the blushing was very light so I was able to clear it up with the blush eraser.
     
  6. eallen

    eallen Friend of Leo's Silver Supporter

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    I am just a couple hours south in Indianapolis with the same humidity levels. I regularly spray nitro without any issues, just never on a rainy day. The key is light coats that gas off in between. Since I use a spray rig, when it gets towards 80% I mix in a little retarder and keep going.

    For those who say you can't, I've been doing it with out a hitch for years. It may not be optimal, but such is midwest weather.

    Eric
     
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  7. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    What brand are you using? It's really critical, as a couple of brands are VERY slow drying and that's another issue. Traditional lacquers dry only by evaporation - there is NO "cure time" - and temperature, humidity and film thickness of each coat area all factors in how they perform.

    Normally you should always follow the manufacturer's specifications when it comes to acceptable humidity levels. There are ways around it - to a POINT - but no matter WHAT brand you use:

    1) each coat should be applied via 3 extremely thin passes per coat. An individual coat will not provide full coverage or flow; this isn't "paint", it's finishing lacquer and applied in a completely different manner than enamels and other "paints". Lacquer melts into itself and will blend and flow into one single coat as the film builds.

    But if you you apply any of them too thickly - especially in a high humidity environment - you will suffer from both solvent and moisture entrapment. The first slows the dry time, lengthens the time between coats ( or stops it until coating is stripped) and causes blisters and peeling; moisture entrapment due to humidity causes blushing, drying issues, discoloration and several other issues.

    2. Keep blush eraser (or remover) at hand in case you see any areas appear "ghostly" with white deposits or clouds in the film. But do not ever spray blush eraser directly on the surface. The piece needs to be moved from the normal spray position (90 degrees from the floor - never spray finishes "flat") to a flat position, and the blush eraser sprayed from about 1.5-2x the normal distance *across* the piece so the blush eraser only "drifts" lightly down onto the surface.

    Use it VERY lightly or your lacquer will run all over the place. And if you spray directly at the surface you'll likely create waves and other uneven patterns in the coatings - but not remove all the moisture "blush".

    However, I would never apply lacquers if the humidity is at 70% without extensive experience. Even 60% is shaky ground - I've been doing this stuff for over 45 years and if the humidity exceeds 50% I wait - because there is a good chance there will be problems and it's just not worth the hassle.

    For the moment though, no very specific advice can be given - this is all general stuff. Without knowing EXACTLY what products you are using we're guessing

    Also be sure to apply the ENTIRE system - sanding sealer, dyes or stains, grain filler, sanding sealer again, color coats or toners, and clear coats and final buffing -on scrap wood before starting on the real thing. Learn how products work and interact, refine your technique and learn how to solve problems BEFORE jumping into the fire! And if any of those materials were unfamiliar you probably need to do some more reading and study of lacquer coating systems.

    Good luck.
     
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  8. Frickensmith

    Frickensmith TDPRI Member

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    Thanks so much for the information. I am using Colortone Clear Gloss aerosol lacquer, which due to budget, time, and experience is really all I can muster right now. You have mentioned in another thread that Colortone does not behave like traditional lacquers. Have you had any experience with simple rattle can lacquers? If so, are there any peculiarities I should be aware of? I haven't sprayed yet, still waiting for humidity to drop to a reasonable degree.

    Again, I appreciate the response and the good info.
     
  9. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Are you using a complete Colortone system? You can't finish a guitar with ONE product. please list the exact products you plan to use - only then can wwe tell you what to generally expect and give application advice.

    If you have NOT purchased the stuff yet - STOP, and list the products you were planning to use. We may be able to dsave you a bunch of time and money. Also, Colortone lacquers are among the most expensive aerosols on the market, so your comment about budget is confusing - unless you don't understand the number of products required.

    I do not recommend Colortone or Deft products because of the slow dry and "odd" application instruction and details (like notes that Colortone needs to "cure" for a specific time period - which is incorrect, as lacquers dry ONLY by evaporation of solvents. There is no cure time!)

    Two GENERAL rules for any products (which I'm repeating):

    1) apply aerosol and other spray lacquer in VERY thin coats consisting of 3 extremely thin passes per coat. A single coat should NOT cover or flow out completely - that comes over time as coats melt into each other. And NEVER sand between lacquer coats even if you read directions to the contrary!! Properly sprayed the system will flow out evenly and sanding is unnecessary (except for fixing tiny runs, if any), and sanding introduces contaminants into the finish system. Lacquer is NOT paint and should not be applied like paint.

    2) Do a complete mockup that includes every part of preparation and every coat, and include final buffing - BEFORE starting on the actual guitar. Learn on scrap wood or you could end up with an irreversible problem. You should get to the point where no finish sanding is required - just buffing. Finish sanding is a repair operation and if necessary there's still a problem with spray technique.

    Last - if you are using ALL Colortone products as recommended by Stewmac you should follow their directions - except for thickness of sprayed coats and sanding between coats. Normally a new lacquer applicator is referred to the Guitar Reranch site to read their "finishing 101", the best basic directions out there for a "normal" lacquer system.

    But Colortone is a "lacquer enamel", with a high naphtha content that slows down the dry time. Normal lacquers dry in 30-60 minutes per coat, but Colortone products take hours...or days. And as I recall several weeks before buffing.

    Folks here may post tips and tricks for lacquer application, but if they are not speaking directly about Colortone most should be ignored.

    So list your proposed system and maybe we can help. But unfortunately, if you're going with a Colortone system there's not much help here - a few folks have used it but often don't follow Stewmac's directions.

    Good Luck.
     
  10. old wrench

    old wrench Tele-Afflicted

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    If your schedule allows it, you can zero in on the best time of the day to do your spraying.

    Where I'm at, the humidity generally drops in the afternoon hours.

    For example - today at 8 am the RH was about 75%. Right now, at about 4 pm the RH is right at 36%.

    Today is a rather extreme example, but this holds true for most of the summer and fall in the Midwest.

    If you use a weather site like WeatherUnderground, you can plan your spraying a few days in advance.

    I've found this to be helpful especially when using rattle can lacquer where you can't custom blend your lacquer with slow thinner or retarder.



    g
     
  11. dan40

    dan40 Tele-Afflicted

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    Mohawk finishers choice was only $6 a can for the clear gloss and is some of the best performing lacquer that I have had the pleasure to work with.
     
  12. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Except this is where the specific product makes a huge difference. Conventional lacquers can be applied at 36% and dry fast enough thwt the solvents are gone by the time the humidity comes back up (although that wide a swing is really unusual).

    But Colortone is a lacquer enamel, and it takes several hours to a couple of days for each coat to dry, depending on film thickness and temperature.. Chances are the humidity will rise to an unacceptable level during the drying period and solvents will be trapped in the film, resulting in blush and other issues.

    Himoidity is not just a problem during application - it needs to be at an acceptable level during the drying period.
     
  13. schmee

    schmee Doctor of Teleocity Silver Supporter

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    It's a black art if you ask me. I dont know if it's humidity or what. Last time I did nitro (years ago.... I've quit nitro) I had about 7 great coats on. Decided to do "just one more" . Same summer weather, I did nothing different. The final coat got tiny fish eyes all over. It's like the nitro just pulled back from those areas. Let it dry, resanded re cleaned tried again.. same thing. The final coat ended up being Tru Oil! There's a reason paint shops have positive pressure booths and dried air.
     
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