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What finishes, if any, are doable in high humidity?

I live in Atlanta and am currently working on something for myself. It's basically ready to finish. I've been holding off because the weather here has been etrocious in recent weeks. When it's not raining, it is excessively humid - 70-90 percent. I want to use it for a gig I have in the next couple of weeks. Is there any kind of oil finish I can rub on for now that will be fine to either sand off or finish over once the weather is more cooperative and I can spray a real finish on it?

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Shellac will live happily under most traditional finishes and you can work in a controlled environment in doors with little risk of blowing the windows out or asphyxiating yourself. After your gig you could carry on with the shellac or flatten it and carry on with what you normally use.

Or you could just do an epoxy fill and leave the spraying for now. Won't look great, but will do the job.

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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

I always found that shellac would blush very easily in high humidity. I thought very seriously about learning how to French polish. I am not sure what the rules of finishing indoors are since the only finishing I have ever done has been outdoors. What I have recently learned is that the humidity remains the same from temperature to temperature. So if it is 80% humidity in 90° heat the relative humidity will be even higher inside a 70° air conditioned home. This is because hotter temperatures can hold more moisture.

Do you see why I gave up on it? I guess I was thinking oil because at least then the wood is somewhat protected and I can resume the finishing process once the humidity gets to an acceptable level.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Typically air conditioners have a condenser which gets really cold and removes moisture from the air. Humidity in air conditioning will be lower.

Don't spray laquer inside though, that would be foolish.

I've sprayed in 80% humidity using my hvlp system, worked fine.

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Old growth, shmold growth!

Interesting. I use a conventional spray system (gun and compressor) to spray lacquer. I've always been taught not to even try it over 60% humidity.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

I live in Raleigh with similar conditions. I am spraying shellac right now. It blushes a bit when spraying, but the haze goes away as it dries. Spraying thinner coats seems to help.

And humidity in the A/C in my house is generally between 35-45% at around 75 F inside when it's 80-90% relative humidity outside at 90+ F... air conditioning sucks out a lot of moisture from the air leaving the inside relatively dry. If it didn't I'd only be able to build for about 4 months out of the year.

The second part of that statement is correct, the first part is a little misleading.

If the same air that is 80% humidity at 90° is cooled to 70° without_removing_moisture, the relative humidity will go up. However, most methods of cooling also result in some moisture removal.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

HVLP turbine system heats the air at the gun and so lowers the the RH, as opposed to a compressor system where it the air at the gun is cooling as the pressure drops, increasing the RH.
Hence the advisability of driers just before the gun with a compressor system.
One of the advantages of an HVLP turbine system in humid conditions..

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Ok.... That seems to be what I'm missing. So if I went indoors with the necessary items to French Polish, I should be able to get away with it.

I also have moisture traps on my spray gun. I empty the water daily in humid conditions as well. Who knows? I guess I could give that a shot. I suppose the worst thing that could happen is that I'd have to strip it with some acetone which would take all of 10 minutes.

Thanks to everyone for your input.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Lacquer can be successfully sprayed at higher RH. A desiccant at the gun will help, but most of what causes blush is not coming from the air supply if you have a decent water trap on your lines already. As the material atomizes at the tip, moisture from the booth air or make up air gets "cut" into the material. This is what usually shows up as blush and is only a problem when temps and humidity are high because the coating will solvent dry before the moisture can evaporate back out. At these times you will need to add some retarder to your material to slow the solvents evaporation rate to allow time for the entrapped moisture to work it's way out. This will of course increase necessary dry times between coats. Some people will heat their lacquer but I find that solution impractical. As mentioned turbine systems do better due to the fact that they heat up the air making it more resistant to picking up moisture as opposed to regular spray equipment where there is often a bit of temp drop of the air stream at the cap. But hot material or air can lead to other problems like solvent pop. I prefer to adjust my spray mix with solvents and retarders to achieve the results I need.

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Brian

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

https://www.howardguitarsdelaware.com/

Ok. So, I messed around with French polishing today. Only got the first couple coats on with the long straight strokes. And I have to tell you that I suck at it.

There was apparently a thread (or two) where a lady was doing a French polish on an acoustic and it looked phenomenal. I can't find it though. Was hoping to read that to get some tips. Does anyone have a link to the thread? I searched but couldn't seem to find it.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

viewtopic.php?f=10101&t=40686

I'd give spraying lacquer a shot:) My dad had a cabinet/furniture shop outside Nashville for years and had to finish year round.

And, of course, I just sprayed 2 coats of full strength lacquer on a scrap piece an hour apart, sanding in between, in 88% humidity and haven't seen the first sign of blushing. Is it because the "lacquer" we spray today is already pretty thin in the first place? I read somewhere that years ago it used to be a lot more viscous and almost always required thinning.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Actually, the solids content of most coatings has increased in recent years to make the coatings more environmentally friendly. There is also a difference between thinners, they come rated for temps or "speed", and then there is retarder which can be added as well. The reason it was usually thinned in the past was due in large part to the equipment used. A siphon gun needs much lower viscosity material to function and atomize than a modern gravity feed or pressure feed system like an hvlp. Blush will show up more on darker woods because out its harder to see over a light background.

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Brian

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

https://www.howardguitarsdelaware.com/

Hmm... I've been buying my Lacquer at Southern finishing here in Atlanta lately and the staff there really seems to know their biz. They told me the opposite.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

Which part was the opposite? I know the lacquer I am using at work is a much higher solids than what we were using even last year, and I was told pretty much the same about it as Brian. It's taken a little adjusting to for me especially on porous woods but we're almost to the point where we can do one less coat than we used to to achieve the same build, depending on the wood. I'd also agree that a gravity feed does a much better job of pushing higher viscosity materials through than a siphon. I hardly even touch my siphon feed guns since I picked up a nice GF.

Out of curiosity Brian, what retarders do you like to use? I've been using butyl acetate mainly with a tiny bit of butyl cellosolve on really hot days. Our supplier told me to use butyl acetate as my main solvent but I found it slowed down drying too much for our production schedule in that role, so now I just go with lac thinner as our base solvent and use these to make adjustments. (not that what you're using would work for where I live necessarily but I'm always interested in finding out more tricks of the trade)

Interesting. I've also noticed there are many different lacquer "formulas" on the market. For instance, I've been using Mohawk brand classic instrument lacquer. But there is also piano lacquer, pre cat, post cat, etc. None of which I've ever used. I imagine they all differ in solids vs thinner.

On the subject of thinners... People have suggested straight acetone, which I've tried. Seems to work great but I can't really tell what the difference is. Is it supposed to dry faster or slower? Also noticed different formulas in off-the-shelf thinners as well as people that choose to mix their own. I don't know... It seems like lacquer dries quickly no matter how you spray it.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

I use mainly butyl aceteate as a retarder. My coatings supplier has some retarder blends that I like and the best for the hot and humids is the #1 which is mostly butyl acetate along with some other light aromatics. It does seem that it may have an effect on overall drying, but I think the high solids coatings are slower to "cure " from the get go due to the necessary changes in chemistry. I spray many fewer coats but wait longer to buff out it seems. I typically add no thinner or anything unless I have issues with blush or solvent pop. When I need a straight reducer I use PPG's thinners in the appropriate temp range. Glycol ethers can be used as a retarder as well, some of the blends are higher in those than the butyls.

As for acetone as a reducer, acetone is really aggressive. Some like to use it because it really lowers the surface tension and makes the coatings really flow. As such it also limits how much you can hang on the surface before it sags. It also will reactivate everything already down, even the pore filler if it is a traditional type. This can cause all your pores to appear to shrink after about 6 months or so. I never saw the benefit of those final two flow coats with 10%-15% acetone. The flow coat will just flow out very evenly over the texture already present from the previous coats, unless level sanded first. And that's just an extra sanding operation you really don't need. This trick was of way more use to those looking for an off the gun finish on cabinets and furniture than musical instruments.

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Brian

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

https://www.howardguitarsdelaware.com/

to piggyback on what Brian said about acetone, I've had some pretty big problems on hot days with using only acetone. Mainly blushing and having trouble keeping a wet edge

I've never used the PPG thinners, I didn't realize they had blends for certain temperatures. I'm going to look into that.

Get them at my local autobody refinish supplier. They used to be rated by temp, now they are slow,medium and fast but the guys at the store can cross it back to temps. DT870 is a medium evaporation rate reducer that I use on occasions when need one. Most other brands will have similar products. PPG is only two blocks from me and I like their stuff.

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Brian

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

https://www.howardguitarsdelaware.com/

So Acetone dries slower? I read a really good article about various Fender finishes where the author had a recipe/procedure for doing the illusive "butterscotch blonde" finish and he recommended 50% Acetone in your paint coats. Said it exhibited excellent drying times. I guess that makes sense since paint can get thick and a 50/50 mixture will make it flow out much easier. I would also guess that since Acetone flashes off slower you can use higher pressure to atomize your paint correctly without as much orange peel since it stays wet for longer. Just a guess. I'm relatively new to finishing.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

I've been spraying lacquer on instruments for over 30 years now in Hawaii with almost never a day that has less than 75% humidity, and 10 years before that in Washington State where it was not much better. Usually it's in the 80-90% range. I've sprayed most nitro brands over the years and tried all kinds of solvents. Currently I'm using Sherwin Williams,and a FUJI HVLP. Some days the temp and humidity balance is just such that I can get away without blushing, but that's very seldom. I was spraying today in fact, and it was 75 degrees and raining with occasional bursts of sun that drove the humidity off the charts. Here is a little, but annoying trick, that works for me 100% of the time. I have a hand held hair dryer at the spray booth door. I spent a minute or so heating the surface of the instrument, going over each surface a couple of times, then go in the booth and spray immediately. I am also using the SW retarder thinner at the rate of a couple of capfuls per 3/4 full quart cup, but the additional heat is still necessary.

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“ The meaning of life is to find your gift and the purpose of life is to give it away” Pablo Picasso

I sprayed a few coats this past weekend with no blush. Yesterday morning I sprayed another one and there it was. As luck would have it, the humidity went way down later in the day. Unfortunately, I was not at the shop until late. The blush was still there when I checked it. Misted it with some blush eraser and it went away immediately. Probably could have hit it with straight thinner but I figured that's what blush eraser is made for. Was able to spray another coat without any issue.

I'll have to remember that trick though. I've heard of people heating the lacquer but not the instrument. Makes sense and sounds much safer.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."

No, it actually evaporates rather fast. Its possible benefit is in the drop in surface tension that it creates. 50% would be way to much IMO, 10-15% was the typical amount. I doubt that Fender or any other manufacturer ever did this as it would require more coats which means more labor and cost......but they did some strange things at Fender like Polly clear costs over lacquer toners and bursts.

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Brian

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

https://www.howardguitarsdelaware.com/

For clear coats I agree. Sealer coats could be good that thin but I was talking about paint which can get thick and mucky. Especially when you get into pigments as in opaque colors. I sprayed some colors thinned 50/50 with acetone and it worked well. I learned to spray colors at higher pressure with the needle throttled way back for greater control and a finer atomization. This can have a tendency to leave a sandy texture so I imagine that's where a thinner mixture can be of benefit.

Like I said, I'm still learning a lot. Thanks for all the helpful advice, everyone.

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"I'm not going to say that perfection has never been achieved. However, if it has, it probably went unnoticed due to it's lack of character."