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I remember a little while back John How finished one of his guitars with rock hard table top varnish. I'm requesting info on that from him or anybody else that knows anything about it. How much longer does it take to finish a guitar with brushing varnish in comparison to nitro? Roughly, how many coats are needed? Is it tough to buff? I'm asking because when I spray a guitar this time of year the shop gets hot and humid. All the cool dry air blows right out the window with the spray exhaust. It's also tough to spray in the dead of winter.

Behlens rock hard table varnish is a good choice as far as varnishes are concerned. There are many forms you can use for varnishes i.e. gel, wipe on, brush on etc. They all have an amber hue to them because of the oil content and are best used on dark woods. You must sand between coats and they also need to be applied in as dust free an enviornment as possible due to their slow dry times. They also must be rubbed out either to a satin or gloss to achieve a nice smooth surface. It looks as though you have decided to brush on the varnish. A good brush is important. Try and get one that is as soft and fine as possible. I usually apply the first coat thinned 50/50 but be careful of drips and runs. I also generally go with the grain. Some people go with the grain and then immediately across it or vice versa. Find what best works for you. Apply in long smooth strokes and try not do reload the brush during the stroke. Keep what on wet with the following strokes. Let the coat dry overnight. You can then sand it back with 220 grit paper. It is not necessary to sand through to the wood. Just a light even scuff sanding is good. The second coat can be applied thinned roughly 25%. Wait 24 hours again for drying. Sand it again and apply another coat. This coat can be full strength. Depending on how heavy you apply and whether or not you are going to be rubbing out to a satin or gloss probably 4 to 8 coats is enough. I like to let the finish cure for at least a week before rubbing out. If rubbing to a satin I start lightly sanding at 600 and work my way up to around 1200 or 1500. Then you can appply a nice coat of wax with fine steel wool and then remove the wax with water and a clean piece of steel wool. If going to a high gloss sand through at least 1500 and then hand rub out with Macguires deep cut, fine cut and swirl remover. (4, 2 and 9 I believe)
For those interested I will be releasing a guitar finishing DVD in the next 2 or 3 months. It will show oil varnishes as well as catalyzed lacquers, urethanes, French Polish etc.   

Good luck and let us know the results.     

Thanks for the info. Is there any reason I should not use a buffing wheel to buff, instead of by hand?

[QUOTE=Colby Horton] Thanks for the info. Is there any reason I should not use a buffing wheel to buff, instead of by hand?[/QUOTE]

I just assumed you would be doing everything by hand but you can also use a buffing wheel with excellent results.

Hi Colby
I am in the process of finishing up my first two varnish coated guitars. I used Behlen rock hard and enjoyed the process of brushing the varnish. It is tough to buff, you have to be very carefull to avoid buffing or sanding thru. Other than that is is working very well. I just have several spots that I have to figure out how to recoat (buffed thru). The varnish does not burn in to itself so all you have is a mechanical bond and possible witness lines if you buff thru. I talked to Bruce Sexeuar and he told me to try adding a small amount of acetone to the varnish (I assume to soften the varnish) and help it get a bite when I recoat the small area I am repairing.
Anyway the others have all given good advice, I have a badger brush that seems to work for me. The brush seems to get considerably better after you have used and cleaned it a few times.
Also the mix seems to be pretty important too. I thin my varnish about 10% and that gives me a real nice flow out without any sags or runs. The mix may vary depending on temps and humidity in your area so some experimentation is in order.
I gave it about 2 weeks to cure then started wet sanding down to 1500 or so and then buffed it using my dry wheel and menzerna compounds.
Unfortunately, like I said I buffed thru in a couple of places and have to repair it. Other than that I really like the warmth that the varnish has. It is definately amber but it looks and feels great.

_________________
Tickle your guitar daily, and it'll tickle you back.

Outside of the process... what is the downside to varnish finishes?

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Other than the process, I can't really think of any downsides. The upside is that it goes on very thin and is probably a better sonic alterantive than lacquer because of that. I haven't tried exposing it to chemicals such as alcohol so I don't know about that. It seems to cure pretty hard but it is a thin coat at least in my case. I put on 7 coats I think but sanded a good portion of that off between coats.
Like others have said, you need a clean envornment and it takes a couple hours to get dust dry. I understand you can put a couple coats on per day but I went with one each day after sanding with 320 grit. By the way, it sands great, better than KTM-9 and definately better than lacquer.

_________________
Tickle your guitar daily, and it'll tickle you back.

There are down sides to everything....

Varnish is made by cooking a drying oil and a resin together to form a copolymer. In theory you get the film forming capability, stability, some of the hardness and the gloss of the resin along with some of the flexibilty and solvent resistance of the oil. A good varnish will have very much the same index of refraction as the cellulose in the wood, so the reflectance and 'depth' can be better than almost any other finish. The downs are that because the final film cures by oxidation (hence the solvent resistance) a fresh coat won't 'burn in', and might not stick properly. If it gets scratched it's hard to touch up compared to nitro or French polish. The oil content adds a lot of damping, which can hurt the high frequency response. Varnishes usually need to go on thicker than French polish (to avoid cutting through when polishing), and that adds weight. Varnishes won't polish up by the use of solvent like FP, or melt and flow with heat the way lacquer does; you've got to use progressively finer abrasives.

I use Rockhard thinned about 1/3 with mineral spirits, and add about 5% acetone ad a small amount (drops per pint) of kerosene. The acetone helps it 'bite' into the prior coat a little, and 'flashes off' fairly quickly. You can 'pull' the coat out pretty thin while the acetone is still there and then the coat thickens up enough to not run (you hope). The kerosene acts as a brushing agent so that you can pull it on a bit thinner.

Recoat time is the key to avoiding witness lines. The first coat will be tacky for quite a while: maybe a day, but after that you can get on two coats a day eight hours apart. Those two coats will melt together well enough that you can treat them as one. Because of the way I thin it the stuff goes on very level if I'm careful, and needs little leveling out in between coats.

I slap it down along the grain, spread across the grain, and smooth along the grain. If you're using colored varnish (as on a violin) it sometimes works better on curly wood to go across-along-across, so that the final brush strokes go along the _curl_ rather than along the grain lines. This helps mask differences in thickness/color. Always work from a wet edge to avoid lap marks. I do the back of the guitar, then the sides, then the neck, then the top, holding it with a hand through the soundhole. When I can no longer hold it that way I hang it up to finish the ast few brush strokes.

It takes longer to clean the brush than to put on a coat of varnish. I use some ~$10 bristle ones, and find that they do get better with use and time. Clean them well:the biggest problem I have is 'sand': the little specks of dried varnish that you never seem able to get out of the brush.

A light French polish fill with pumice will greatly reduce the amount of varnish that soaks into the wood, particularly the top. It's possible that the famous Cremonese 'ground coat' was something like this. I used just five thinned out coats of Rockhard over FP fill to finish my 'Winter' archtop. I sanded the last coat with #1800 and #2400 micromesh, and polished out with Meguiar's and Novus plastic polish.    

Alan,

On your build coats, those after the first coat, you said you put on two a day, and they tend to melt in to one another. Do you lightly sand between those coats?

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Yes, you have to level things in between coats, for one thing: get out the 'sand' and any runs.

I was reading an article a few years ago on composites in aircraft construction, and they talked about the concept of 'surface energy'. It sounds sort of 'New Age' but it's not. When you sand or plane a surface you are breaking chemical bonds, and this leaves some 'free radicals' (if you will) sort of floating for a while until they can find something to latch on to. If you present these poor unfulfilled chemicals with something like glue or varnish or resin that is itself looking to hook up the bonds will be stronger (sort of the chemical version of 'love on the rebound'). Sanding is one way to increase the 'surface energy' before bonding. One test they suggested was to sprinkle a little water on the surface. If it beads up the surface energy is low, but if it spreads out into a film then the energy is high and you're likely to get a stronger bond (after yu dry off all the water!). Time is the important thing here: back in WW II the Forest Product Lab found that you get a stronger glue joint within 15 minutes of working the surface, and I imagine something similar holds for varnish. Scuff sand it to a uniformly dull surface and put the next coat on ASAP, and _don't touch the surface in between_! Pepperoni grease ruins most bonds.

[QUOTE=Alan Carruth]
Pepperoni grease ruins most bonds. [/QUOTE]

That explains a lot of my misfortune!

Thanks Al

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Good info guys, thanks!