Finish Options for High Humidity Conditions

Discussion in 'Finely Finished' started by GotTheSilver, May 28, 2019.

  1. GotTheSilver

    GotTheSilver Tele-Meister

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    Hi, all. I got into guitar building a couple of years ago and have now completed the builds on two electric guitars. I have not painted/finished either one yet. My original plan was to spray nitro lacquer, but I live in Houston, where the average relative humidity each month of the year is about 75%. March has the lowest average humidity at 72.7%. I tried over the winter (as much as Houston has a winter!) to spray nitro on some scrap mahogany boards as practice. It took me three months to get enough days with low enough humidity to get enough coats of lacquer on the scrap, given that I can only do this on weekends.

    The best I can do is spraying in a spray booth in my garage, where I cannot control the humidity. I have not tried retarders yet.

    So I am finally starting to consider other finish options other than nitro that would be less susceptible to high humidity. I know someone here in town who uses automotive finishes, so I may look into that. I thought about waterborne finishes, but I read that they also have limitations with humidity (is this correct?).

    My question is - what types of finishes should I be looking into for the given high humidity weather conditions? Also, if you can name specific products of that finish type that are high quality, that would be very helpful. Should I try the nitro again, this time using retarder, or is that a losing battle at these humidity levels?

    Thanks in advance for any help!
     
  2. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    You may know all this stuff but others might not - so some review:

    there are also wide variances in dry time, as lacquer does not "cure" - it dries by evaporation of solvents and additives.). They also can be applied over each other and don't "care" - the resins intermix just fine, creating one coat of "lacquer"(I'm not going to get into the rheology of formulations and complicated chemical analysis. the solvents melt each coat into the previous coats, and the resins blend into each other..)

    So some "automotive finishes" - i.e. acrylic lacquer - will have you in the same pickle you are now.

    Professional shops shoot both types year round by using dehumidifiers and heaters as needed. But pros also keep a range of solvents on hand to speed up or slow down the drying process. Places like Disneyland, Universal Studios and other theme parks do lacquer work year around - some in controlled conditions, some contracted out, but much of it by their own crews, who have turned "coating in poor conditions" into a specialty "art".

    The goal is preventing both moisture and solvent entrapment. Solvent entrapment is caused when the coat(s) "skin" over, leaving a film that makes it very difficult for the rest of the solvents to penetrate/evaporate. It's normally cause by overly thick application, especially in hot conditions. It's one reason most of us stress multiple "pass", very light "coat" application - a "pass" just drifting material onto the surface, with 3 or so passes creating a (with opaques) a transparent coat. If it has nice coverage and is smooth - it's too thick unless it's the final "flow" or "flood" coat of clear.

    Thick application can also trap moisture, causing "blush". Blush preventers/removers/whatevers are simply slow-drying solvents with a TINY bit of either nitrocellulose or acrylic resin and some flow agents. They are NOT "applied" - sprayed ON the surface. They are lightly sprayed high above and parallel to the surface (the only time the piece is sprayed when flat) and allowed to drift down onto it They melt the skin and/or soak into the entire film, releasing the whitish moisture. Spray too heavy (everybody does it - usually just to experiment) and the previous material runs right off the surface!:eek:

    If you can talk to any professional furniture refinishers, antique dealers and such plus professional contractor paint dealers (NOT retail-oriented paint stores or hardware stores) ask about what solvents and "release" agents they stock. You might even call the local chapter of the PDCA (Painting & Decorating Contractors of America) and ask if there are any lacquer specialists in the area - although they are becoming scarce.

    And measure your wet film thickness with one of these wet film gages, available online. Learn how to calculate the dry film thickness from the wet film - you'll probably be shocked at how thin it is...and DON'T apply at the thickness recommended on the product data sheet in bad conditions - you want to go at a fraction of it (you'll find out how much through practice):

    wet film thickness gage.jpg

    It will take a LOT of experimentation and test applications. It will also take the right spray equipment. High pressure conventional spray will work, but it's a mess because of the amount of overspray, lack of control and incredible waste of material.

    Every pro I know who does finishing regularly uses a high-quality, turbine-type "non bleed" HVLP (one where the air is triggered with the material. 90% of the cheapos are "bleeder" guns where the air is running constantly and the material is hard to control. Bought one for experimentation - and for providing forum advice and it's a beginner-only POS compared to good units.

    A REAL HVLP sounds like a vacuum cleaner because it essentially IS one in reverse! Compact units have a turbine, large diameter air hose, and a cup gun (gravity guns are a hassle). They spray at 4psi (cheaper ones up to 10psi - but anything over that is not HVLP) and a good gun can very nearly coat to an edge without masking (but not quite!). They move a ton of air - but at low pressure, and gun/air cap/needle quality is paramount (good quality guns - without turbines, hones and with only one needle/cap set) run $200-400. But you can find used rigs (turbine, hose and gun) for $350-1000 and then spend $150 or so for a lacquer needle/cap set.

    I'm making a big deal out of the equipment because it's very difficult to work well in marginal conditions with cheap equipment. The Harbor Freight so-called "HVLP" guns are nothing but fishing line anchors if you plan on doing difficult work.

    Those are the essentials: Having the range of solvents on hand for your conditions, measure wet mil thickness to verify light coat application; have several aerosols of different blush erasers and learn what each does; use the best HVLP system you can afford (and get training in HOW to use it properly if you can).

    Last - ALWAYS wear a cartridge type respirator and full coverage goggles. Dust masks and old t-shirts over your nose and mouth are the same as directly inhaling lacquer!

    Hope that helps -
     
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  3. GotTheSilver

    GotTheSilver Tele-Meister

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    Thanks, Silverface. I appreciate the thorough response. I had to read it a couple of times to absorb it all! :)

    I do have an HVLP (Fuji MM4), however, I don't really have experience in finishing other than spraying the scrap pieces I mention. I am far from an expert who knows how to use the various solvents and chemicals.
     
  4. philosofriend

    philosofriend Tele-Holic

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    Like Silverface said, try to find the professional contractor paint dealer in your area. Mine is just across town and they have the obscure additives you read about in old books. Their best lacquer solvent is is so much better than the best at the big box store. The guys at the counter are always helpful.

    The trick I figured out that has worked for me so far for damp and/or cold nitro spraying is to keep the work and the lacquer warm. I have a cheap tripod work light with two halogen bulbs. The 500 watt bulbs they come with burn out quick, replace with 300 watts. I use the work light to keep the guitar warm while spraying.

    If it is cold out I start by bringing the lacquer and the thinner cans inside to warm up, and I place the guitar over the furnace vent to warm up. Out in the garage I shine the worklight on the area where I will do the mixing and load the gun. The lights never get closer to anything than about two feet. They are used to gently warm things, not scorch them. If I can't comfortably keep my hands on the work, the lights are too close. When the gun is loaded i put it three feet from the lights and go inside to get the guitar. The guitar hangs with the light shining on it and I immediately give it a thin coat. When the spraying is done the light goes out, trying to dry it extra fast causes its own problems as Silverface said. I leave the guitar in the garage until I can't smell solvent anymore with my nose right up to it before the next coat.

    Gibson used to spray warm nitro. They used the same safe system that the furniture factories used. A warming coil went into a large container of mixed finish. The system was made on purpose by spray gun companies that did not want to be sued, this was not just some Kalamazoo hicks boiling a can of lacquer on a hot plate.
     
  5. Drak

    Drak Tele-Holic

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    I've been shooting lacquer on guitars for ~25 years now.
    I've shot in every possible kind of climatic condition and so have a lot of experiential data in my head about it.
    I've used blush erasers and retarders, yes, and don't like using either of them and I avoid them both.
    They're band aids, nothing more, and using band aids is not the way forward to success.
    Using band aids means there's something wrong with the process, because they shouldn't be needed, at all.
    Yes I've experimented with heating lacquer, what a PITA it is. It's not worth the trouble.
    Yes I've shot it outside and run it inside.
    Yes I've tried nearly anything you could throw at me.
    And I learned, you either have a successful way, or you don't shoot, period.
    95% of the cheats don't work or will leave you with some sort of weird result.
    Weird is not success, success is success.

    With what you described in your post, I would (sadly) tell you its a complete no-go, at least for lacquer.
    Just hang it up and stop beating your head against a non-forgiving wall of moisture.

    Maybe catalyzed urethanes would be a way forward.
    They cure in a completely different way than film finishes (lacquer) do.
    Where film finishes are brittle by nature, cat urethanes are more like tire rubber...they're 'tough'.
    Its a different thing.
    But you must be Religious about thoroughly cleaning guns and equipment, seriously on-top-of-it.
    And top-shelf respirator gear as well.
    And none of its cheap.

    Or just have someone else finish the two you have on hand.
    I love shooting lacquer, I swear I love it to this day and always look forward to it.
    But I fully well know what you can get away with and what you can't and when its a no-go.
    In my area, I always watch the local dewpoint, and when its above a certain %, its a No-Go, period.
    Your situation is a no-go 100% of the time, I wouldn't even attempt it knowing what I know.
    I will never move to your land of Texas, that I can tell you.
     
  6. eallen

    eallen Tele-Afflicted

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    There is ideal and then there is reality when it comes to finish conditions. If auto finishers had to wait for low humidity days to spray lacquer in the old days they would have never finished a car in much of the midwest. But they did. I have sprayed if for years at 75- 80%. Is it ideal? Nope. But it is either that or do no finishing for months.

    Thin your mixture, spray thin layers, wait adequate time in between. If need be add retarder or blush remover. I seldom have to. If it is raining don't spray.

    Eric
     
  7. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Based on your level of experience I strongly suggest waiting for better conditions.

    These statements are untrue, and 25 years experience spraying lacquer is commonly done on a purely amateur basis.

    "Blush erasers" are repair materials - NOT "band aids", but permanent "fixes".

    And "retarders" (slow evaporating solvents of which there are dozens of various blends - along with accelerators...faster evaporating solvents... and various chemical types of viscosity - "thickness" - adjusters) are ALL professional tools used to tweak coatings formulations to improve application performance without sacrificing long-term durability. They are NO different from using dihydrogen monoxide to adjust the viscosity and coverage rate of many vinyl and acrylic coatings for for architectural applications.

    You may not "like" using them - but have you ever been professionally trained in their proper use? Most commercial contractor oriented paint stores (that deal in specialty products like lacquers, plural-component polyurethanes, polyesters and polyureas, glazes, multicolor spray finishes like Zolatone and Multispec and the high-end spray equipment needed to apply them) offer free or low-cost training seminars for applicators who are planning to purchase those products.

    They always provide free spray equipment training to spray system purchasers (and usually have a few "at cost" slots for those that already own their gear.)

    Professionals and well-educated amateurs are aware there are different solvent types, air caps/needles, equipment settings, techniques and who to use as resources for information. They don't just "wing it", but they don't throw up their hands and say "it can't be done!" - because it CAN.

    It takes the right tools, equipment and training - but, as previously stated, the cost of special equipment and the research time involved just aren't practical for total beginners. Nor are the repeated practice applications, as mistakes WILL be made when experimenting with application in marginal conditions.
     
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  8. Drak

    Drak Tele-Holic

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    Everyone's entitled to their opinion.
    But I see far too much malignant optimism these days.
    Like 'there's Always a way'.
    That is not a mature realistic view.
    Sometimes there is not, and sometimes that needs to be faced, because that is the correct answer.
    Malignant optimism leads people to spend time, money, and effort down the rabbit hole of endless frustration.
    And leads them to believe that 'it will work if I just try harder'.
    Reality and clarity of thought is sometimes different than malignant optimism.

    And everyone has their own opinion.
    I've shot thousands of finishes over the years, I'm quite happy to stand on and state my experience.
    Based on and working with, the facts given to me in the OP.
     
  9. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    As I clearly stated, those conditions and the materials required to coat under them are NOT good situations for the inexperienced or untrained.

    But simply stating it can't be done is absolutely untrue, and terms like "band aids" and "cheats" are incorrect, misleading and demonstrate a lack of knowledge. If you know what you're talking about why not state that while professionals do work under these conditions on a daily basis, they are not the type of thing the OP should attempt?

    THAT would provide some actual education. But your "it can't be done post" - which can be located using Google, out of context - can mislead and dissuade those who might be interested in LEARNING about and eventually doing finishing work on a professional basis.

    I suggest if you are going to say "it can't be done" put it IN CONTEXT - "it should not be done by beginners"

    ...and apparently CAN'T be done by some with decades of experience but little education in the subject. Or maybe little skill, or bad tools. We have no way of knowing exactly what's missing, but something sure is from anyone who simply says "it can't be done".
     
  10. GotTheSilver

    GotTheSilver Tele-Meister

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    Thanks for the input, guys. I think I will try shooting the lacquer with retarder on some scrap. I already have the sprayer and all the materials, so what have I got to lose? If it doesn't work, I can play with different mixes. Again, it's scrap, so nothing to lose.
     
  11. Drak

    Drak Tele-Holic

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    So if you're going to use retarder, let's do it with an approach to SUCCESS, not just 'spitballing' it and 'hoping for the best'.
    Screw that 'hoping for the best' business, I always shoot for SUCCESS, and so should you.
    I don't have the time to waste my time, so if I'm going to do something, I plan on being 100% successful at it.

    The shooting on scrap is an excellent idea, but you need a methodology in place in order to repeat it successfully if you hit upon success.
    First things first:
    What kind of thinner are you using, and does it list a 'speed' on it?
    Is it a quality pro-level thinner or junk Home Depot (paintbrush cleaner) thinner?
    Can you post a picture of the thinner can with the label that can be read?
    Can you post a pic of the retarder can?
    I use pro-level Medium Speed thinner which, with the amount of retarder already in it, works perfect 99.5% of the time.
    That's 'my' cutoff point. If my work blushes on me using medium speed thinner, its time to stop for that day and wait it out.
    Now, I already know at what dewpoint I'll get blushing as I've formed my own repeatable methodology for myself.
    I've done all the data collecting for me where I live. I'm not guessing at it.
    Yes, I do have retarder, but I rarely, rarely ever use it.

    Retarder, used in SMALL SMALL doses, (like, you can count the drops worth) works.
    Used TOO MUCH, leads to a finish that feels plasticky and sticky and never fully dries properly.
    Your job is to discover for yourself where that line is, and hold to it.
    All those threads you read about factory finishes that feel plasticky and sticky?
    Too much retarder. Cop-out. Insurance. Lazy. The 'easy' way out.
    But there's a price to all of that, and that is a sticky, plasticky, finish that never really dries.
    You don't want that.
    So you need to be very aware of exactly how much retarder you're using, like, the exact number of drops.
    And be able to repeat that and do not exceed it if you don't have to.

    I don't live where you do so this will be up to you to figure it out for yourself.
    I can guide you on the methodology, the results will be yours to report.
    Start checking your local dewpoint or humidity or buy yourself a humidity meter to keep in the shop.
    Start making a list.
    How much thinner? Exactly how much.
    How much retarder? Exactly how much.
    How much product? Exactly how much.
    What was the dewpoint when you shot that day? Exact number.

    You will begin to see the 'pattern' show up, you are LEARNING!
    Once you have some repeatable data on your chart, you'll begin to skin the cat for yourself.
    The GOAL is Dead Minimum Retarder, and no more than that.

    If the conditions are as bad as you stated, and you need some ridiculous amount of retarder...
    Or no matter how much you use it still blushes...
    Its still a No-Go in the end.
    But...maybe you'll figure it out and skin the cat.
    I hope you do!
     
  12. old wrench

    old wrench Tele-Holic

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    I'm strictly an amateur finisher, so I'll stay out of the finishing discussion - but I also have a natural curiosity which feeds a philosophical nature.

    It seems to me that "malignant optimism" is a sort of social disease; it doesn't kill outright, but instead leads to a myriad of complications such as grandiosity, pomposity, and diminished mental capacity. It would be bad enough if it were confined to it's original host, but it's often passed on to new victims by appealing to some vague and distorted ideal or value. Once infected, the new victim becomes a type of useful idiot (just repeating a popular term here), who defies rationality and sensibility and becomes willing to cut their own throat in order to propagate that distorted ideal or value. Please, don't look to modern medicine for a cure unless a way can be found to capitalize and monetize it and turn a hefty profit. I believe the solution requires the application of heavy doses of objective reality and clarity of thought. I think I'd up the ante and take it a step further by saying reality and clarity of thought are always different than malignant optimism ;).

    Sorry for the hi-jack GotTheSilver.




    Best Regards,
    Geo.
     
  13. Luthi3rz

    Luthi3rz Tele-Meister

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    So what happens when you spray lacquer when it's 75% Humidity?
     
  14. Drak

    Drak Tele-Holic

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    Generally, the faster the thinner evaporates, it 'traps' the ambient moisture in the air in the finish.
    It's called 'blushing', (looks very cloudy) but really is moisture trapped in the finish by the thinner evaporating so quickly.

    Retarder slows the process down and allows the moisture to evaporate before its gone and the remaining lacquer product dries.
    The down side is if used too much, and it doesn't take a lot, you've slowed down the process so much the lacquer never 'really' completely dries properly.
    Lacquer is a 'brittle' finish by nature, too much retarder leaves it soft and spongy, plasticky and soft.
     
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  15. Luthi3rz

    Luthi3rz Tele-Meister

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    Why can't you control the Humidity there? Do you own a De Humidifier?
     
  16. eallen

    eallen Tele-Afflicted

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    Your spray method can influence the answer to that. Where I live, done rightly, nothing happens except you get a nicely finished guitar. It is just an everyday summer occurrence.

    If you use too fast of a thinner and heavy coats you can end up with blush. Medium thinner, light coats, typically no big deal where I spray all summer long.

    Experiment, learn, have fun doing it, post pics so we can have fun watching.

    Eric
     
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  17. jvin248

    jvin248 Poster Extraordinaire

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    .

    At some point in the trouble of finishing you figure out that nitro is not the goal. Having a guitar you can play is the goal.

    Get some wipe-on poly/tung-oil/tru-oil/etc putting it down with thin coats and go that path.

    Even if you are forced to smear dead bugs on your guitar, you can do it. Get the guitar playing :)
    ...Shellac is dead bugs. I have a few antique tables that were originally finished in the 20s-50s in shellac, that while I repaired the tables I tried it on a guitar and it works too. Dries fast you can add a lot of layers in a day. New coats melt into the old coats like everyone chases for Nitro. Probably sticky like nitro to play too... French polish is a mystical term to use on your friends when they see and can play your new guitar.



    .
     
  18. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    That may be YOUR goal - but others may also want a guitar with a specific type of appearance that requires a lacquer finish. THAT is why these questions come up - and telling them their goal is "wrong" is really a bit rude IMO.
     
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