Official Luthiers Forum!

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I use polyurethane. Minwax, more precisely.

It's the easiest thing to apply with a brush (I'm not equiped for spraying and won't be until I have a shop seperate from my home.). It doesn't need sealer (unless for rosewood), the smell is WAY less irritating than lacquer, it sands great within 8 to 10 hours and polishes great just 24 hours after the last coat (as long as it was sanded with 2000 grit). If I apply two coats a day, I'm done finishing a guitar in about 10 days.

The drawbacks is you have to seal rosewood with two coats of shellac otherwise it won't cure (which is not a big draw back...) and it yellows out a bit within the first few months (depending on light exposure). And this is not that big of a drawback in my opinion. It just look old a few years before lacquer finished guitars do.

A small note, stay away from the waterborn polyurethane. Way too soft as for most waterborn finish products.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

We might have another option in the near future. I work for an automotive paint company (PPG Refinish) and we have been spraying cars for several years with water based color coats. Due to environmental pressures, the water has now made it to North America. In fact it is mandatory in CA and thoroughout areas of Canada. Now here is the interesting thing. Speaking to some of our guys on the product side of the business, we are very close to releasing a water based clear. It is a high build made for automotive and if it works like the base coats all you need is air movement. In fact, on projects as small as a guitar you apply a coat and can air dry with a blow gun or fan and apply the second and third coats immediately after flash off. Its really awesome. I think I will do some homework and find out the film build specs. My understanding is that it is just a few months away. ANy thoughts?? Heck, if it holds up on a car, it should be plenty tough for guitars. Shops scuff and buff within hours following application of base coat and clear coat.

It's probably got UV blockers in it, which will keep bright white spruce top from tanning.

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

KTM9. low cost. low tech. reasonable finish. less toxic.

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Greg
http://garibaldiinstruments.com/

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Todd I also like the look of Nitro.Do you have a picture of this drying box and how it works and how much it speeds up cure time?I`m sure a lot of us would like to know.
James

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James W Bolan
Nashville Tennessee

IMO nothing has the depth and 'light' of a good oil varnish once it's been cured and buffed. I use 'Rockhard'.

I use FP when lead time is an issue, and on tops, particularly of classicals.

I've had problems with every waterborn I've tried reacting to sweat, so I'm passing on those until I know they've got it right.

Nitro makes me sick. Too much exposure in the dissipated days of my mis-spent youth. It's also not stable over the long term, I believe.

Alan, would you lets in on your process and experience with Rockhard?

Thanks,

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Oil. cuz me like it.

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Audiences and dispensations on Thursdays ~ by appointment only.


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EmTech 6000, cause me allergic to explosions.

I remember posting something about building a drying box very similar to that and recall getting lots of comments about overkill. I like it, nice job Todd. Mine is almost completed!

Mike

I use Dupont Chroma Clear, an automotive clear coat. It's a two part acrylic urethane that's easy to get a final thin film quickly. Two days of two coats each session gets it done. It's durable and buffs well with Menzerna compounds. It doesn't noticeably off gas for more than a day or two. The smell won't drive the neighbors crazy. It won't crack over time. It has great visual depth even when it's thin. I can get it locally in a small town. It's a high solids finish that I spray with a cheap hvlp gun and compressor. It's best feature is that I like the sound I get from the guitars I use it on as well as those I have french polished.

The downsides are that it's very clear and will show any imperfection you have. It costs more than most finishes. It doesn't have much warmth and the uv inhibitors are very effective. It shrinks over time so you have to have very smooth flat surfaces. You have to shoot a whole panel for repairs. It has some nasty ingredients so you have to have good protection when applying.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Sorry to be so long.

My process with Rockhard is still evolving, but this is what I did on the guitars I took to Montreal.

The big probem with Rockhard, as with most modern oil varnishes it seems, is 'witness lines' caused by differences in hardenss as you sand through layers in the final polishing. The only ways to avoid that are either to not sand through to previous coats, or to allow the finish to cure for a month or three. I don't know about you, but I always seem to be slapping on varnish the week before the show, so I try to get things nice and level.

Level starts with the base. Pretend you were going to French polish and make it nice and flat. For the best effect the varnish should go right on bare wood; sand any filler back to the pores, and don't use a 'seal coat' of anything else.

I thin the varnish about 25% with their proprietary reducer. This would make it runny, so I add about 5% acetone to thin it further, and allow me to pull on a thinner coat. The acetone flashes off pretty quickly, and the thin coat won't run (you hope). The addition of a few drops of kerosene per pint as a brushing agent also helps you to pull on a thin, level coat.

The first coat can take a while to dry. Oily woods seem to slow it down: I've had particular problems of late with some Macassar ebony figerboards and bindings. You MUST allow the first coat to harden before putting the next one over it! If you put new coats on over a soft first coat you just seal in the soft layer, which never hardens. The surface may seem OK, but eventually the whole thing just comes up. I have found that UV really speeds things up, but even then it can take a few days.

Once the first coat has set up properly, you can put on two coats a day, or maybe even more. Dry sand lightly between coats. I like to build up five or six coats (remember, these are thin), and then sand it out level. Wet sanding seems to cause the surface to harden up, and can give a really bad witness line later, so dry sand with, say, 320. THe object is to get out all of the little dust spots and 'sand' from the brush.

Speaking of which, these days I'm using a 1" camel hair brush.

I build up three or four more coats after the level sanding, with the last two going on the same day and as close together as possible. This will make the surface 'grabby' when you're putting the last coat on, and it will be hard to get it really thin, so watch out for runs and sags.

My Micromesh is probably getting too old, and on the last few I've been using plain ol' wet or dry paper. You should be able to level things up with #1000 or #1200: use the lightest grit that will work, and use it wet. I then went to traditional FFFF pumice and rottenstone, with water, and saw no wittness lines at all. I finished up with Novus' #3 and #2 polish. This gives a pretty good shine.

If you can, wait a few weeks and buff out with a soft wheel and white rouge. I did that on the guitars I had at last year's show, but not until after the show, and they looked great. Drat.

Ken, what do you use for a sealer, or will the urethane bond to the wood?

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

Woody, I pore fill with West System epoxy on back and sides. For the tops I do one coat as a seal coat. The adhesion is excellent.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com