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Dear experts,

I am new to guitar building (on my 3rd right now), and even newer to finishing with spray equipment (about to start my 1st). I’m learning that finishing is a lot like selecting a good wine; everyone has their own taste and there is no “perfect” recipe.

So after 2 days searching the archives, I’ve decided this will just be an easier route for addressing some questions. I am using StewMac’s Step by Step Guitar Finishing book for the basis of my questions below. So here are my questions:

1. They recommend using a vinyl sealer rather than a thinned lacquer for the wash coat. Assuming at least some of you agree with this, do I still need to thin the vinyl sealer at the 1:3 ratio they recommend for lacquer wash coats?

The next few questions have to do with the use of lacquer retarder (LR) after seeing that the use of LR seems to be somewhat controversial on some of these forum post.

2. The StewMac book recommends using LR in “humid conditions to prevent blushing”, but they never quantify what exactly “humid conditions” are. So is a LR even necessary if I am spraying in ~90+ degrees and ~75% humidity (Oklahoma summer)

3. The StewMac book recommends “adding retarder to the thinner before the thinner is added to the lacquer in the normal ratios (e.g. 1:1). You should 5-10% retarder to the thinner…example, a quart (32 ounces) of ready to spray lacquer…would be 16 ounces of lacquer + 14.4 ounces of thinner + 1.6 ounces of retarder (i.e. 10% of the remaining 16 ounces)." Do you all agree with this formula? Another post on here recommended one teaspoon per quart.

4. If I do end up using vinyl sealer for the wash coat (thinned or not), do I use the retarder in the vinyl sealer?

5. Similar question for the “sealer coat”: do I use the retarder in the sanding sealer? And should the sanding sealer be thinned?

6. And finally, if I end up using the LR, how long do I have to wait between coats? I saw one post that said 3 weeks wasn’t long enough before the final buffing. So what does this mean for the “build coats”?


Sorry for so many questions but as you all know, with the time and $$$ that goes into each guitar I would hate to screw it up at this point. Please feel free to add your $0.02 to any or all of these questions.

I guess it should also be mentioned that I am using McFadden’s products for everything but the LR; that is Behlen.

My sincere thanks and appreciation,
Greg

Greg, First off, I do not claim to be an "expert" having built only 7 guitars with successful results . But I will share my process.

I like two coats of shellac as a sealer rather than the vinyl,, just my preference,,I have used both and prefer the amber tint and sealing properties of shellac.

As far as retarder, I have never used any, but I will not spray in excessively humid conditions (80% and better IMO).

I only thin the last coat or two...I use Mcfaddens and it is ready to spray. I have the old style spray equipment (not hvlp) and I spray around 45psi. I allow one hour between coats and level sand with 400 on the first three coats. Be careful not to sand through on the first couple of coats. I usually apply 5 coats to the top (remember there is sanding after the first 3 coats) and 7 to 9 on the rest of the guitar. Remember, this is what works for me with my spraying technique, equipment, and experience (remember I have sprayed only 7 guitars, but I have tons of spraying experience spraying cars and trucks).
There are many variables here and you will get varying opinions, use what works for you and gives you the results you like.

After you complete spraying, let the laquer cure for 4 weeks before final leveling and buffing.

Chuck

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Background, I've built 23 guitars( plus a few re finishes) I've use varnish on 4, and waterbased on 2, the others have been Mcfaddens Nitro lacquer.
Like Chuck I don't use the vinyl sealer, I use shellac. Don't spray is it's really humid, and make sure you wait long enough between coats. I wait at least 2 hours, even though an hour is probably long enough. Even if you spray outside be sure and wear a respirator. Nitro isn't good for your lungs.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Hey Greg, I just sprayed my first nitro finish, and I'm pleased with the results, but certainly have much to learn. Anyway, I'm in southeastern Oklahoma and had blushing problems, I'm not sure you want to wait as long as you might have to here to have low humidity. I ended up adding about 1/2 a capful of retarder to my spray cup, regular size, which I would fill about 1/2 full, and very little thinner. That worked for me and took care of the blushing problem.

Joe

Vinyl sealer was developed to help the Nitro Lacquer adhere to the plastic binding, I used it on my 1st 3 guitars but switched to shellac on the last 2 due to using Z-poxy as a filler. The nice thing about shellac is if you use it on the top it helps give a nice aged look, and it seems to pop the grain more than vinyl sealer on the rest of the guitar.

I used Behlen stringed instrument lacquer on all 5 and am more than happy with the results. I already had spray painting equipment and some experience spraying similar materials so lacquer was the direction I chose to follow. My finishes are more than acceptable and the last 2 came out realy well due to using a wheel buffer and Menzerna compounds.

Remember, a quality finish starts in the wood prep. and sanding, a small scratch or flaw will be seen even easier after finishing. Spend the time before getting out the finishing products a finish will not hide a boo boo.

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

there are 2 rules of thumb I've heard for humidity:

1: 60%

2: a difference of 15 between the temperature and the humidity

i.e. use retarder if the humidity is above 60% or there is less that 15 points of difference between the temp and humidity...

also, if it is hot one might need to use retarder to help prevent the lacquer from drying in the air before it gets to the product.

you state conditions of 90° and 75% humidity which meets the second rule of thumb, but I would say is a tad too hot.

retarder is a 'dangerous' chemical in the fact it slows down the curing time and if too much is used the curing time can become obscenely long...i.e. use as little as possible to get the results needed (i.e. no blushing and no drying in the air) and if possible don't use it at all.

if you do get a coat that blushes you can spray another coat that has a little retarder and is thinned way out over it and that should activate the lacquer enough to let the moisture out (which is what causes blushing)...

your points 4 & 5 make me wonder...vinyl sealer is a sanding sealer, and yes you would use retarder in it also if needed...the need being determined by what has been discussed above...you certainly don't need to use vinyl sealer and then a sanding sealer...

you're right, there is no perfect recipe for spraying, but I think you will find that there is a perfect recipe for how YOU spray and your equipment and ambient conditions

I agree with StewMac on the concept of not using thinned topcoat as a sealer..note my use of words as the vinyl sealer is also lacquer...I don't agree with the mix ratios they give, they seem rather too thin for my tastes and would require far more coats to get a final build thickness and that would result in a lot of solvents floating around and getting into the environment...it could also result in a lot of runs and sags...I do like thinning my seal coats as I think it might help with absorption into the wood and make for a better bond, I also like thinning my final coats as this helps with bonding and lets things flow out, but I like spraying the build coats as thick as possible...as far as adding the LR before or after mixing I don't think it really matters, as long as you very carefully stir (for a long time) the mixture before you put it into your spray system (this is just simple chemistry to make sure at 'microscopic' levels there is consistency of the product)...you will need to find out what your spray system will handle as far as viscosity and that will determine how much you need to thin your mix...if I remember correctly the out of the can viscosity of instrument lacquers is ~26 seconds in a zahn #2 cup...if you have a big enough compressor and the appropriate fluid cap and air cap you can spray it just like that...most of us don't as that big of a compressor costs $$$...I find for my compressor which puts out ~ 8 CFM and has twin 4 gallon tanks (total of 8 gallons capacity) I add 15-20% thinner/retarder and I've decided that I don't want to use more than 4 oz of retarder/gallon of lacquer.


practice and experimentation is the real 'secret'...and do so on scraps as opposed to a finished project...and always spray a test pattern on a scrap to dial in the settings on the gun and compressor as things change daily with respect to exact conditions...

I agree pretty much with Mike P . I am one that used to thing shellac was good enough , but it I am now in the school of using the vinyl sealer. Finish is part that will make the guitar look good. Short cutting this step isn't a good idea. I follow the directions pretty much off the can. I use Behlens instrument grade lacquer. I have about 100 under my belt. Finishing is one of the hardest parts of building. I think that is why so many builders will use finishers . I send most of my finish out as I don't have to buy a spray booth and I feel the health issues are worth the extra cost.
Besides I don't have to clean my shop to finish LOL

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John, when you type I listen. Do you think the vinyl sealer looks better, bonds better or both? Also to correct something I said in my earlier post. I've been using Mohawk lacquer, not Mcfaddens. I'm talking to Mcfaddens about polyester, but I've never used their lacquer.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/