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I decided to thin out the varnish for the top & on the second coat spots pealed off clear down to the bare wood. URGH! I didn't follow Behlens directions to use their thinner, I used acetone. What really stripped my gears was this happened on #7, my finest, up to now, build yet. Has anyone tried anything else to thin Behlen's varnish and ran into this issue, if not learn from my mistake. Clinton

The can says use mineral spirits. I guess you answered your own question.
Chemistry is sort of complicated, you can't just mix stuff willy-nilly.

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I concur with Todd. I would use mineral spirits or if I wanted something that would flash off a little quicker, naptha.
With something as fine as a guitar I would get the absolute best grade thinner I could find. Hardware store stuff especialy acetone can be less than pure but in any case I would use mineral spirits. Sorry for your problem. That can be very frustrating to say the least.
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I waited two weeks for the second coat, life got in the way. I got the idea to use acetone from Allan Carruth's thread but maybe I missed something! Clinton

Clinton,

Sorry to hear about your misfortune.

If I recall correctly, Alan Carruth doesn't use acetone as a thinner, only to help the varnish flash off and also to help the new coat bite into the previous one.

As for the peeling, I'm wondering what the final sanding grit was before finish.

Pat

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Use no more than 10-15% acetone in your thinner, to burn in to the previous layers. If you used straight acetone for thinner, it stripped off the layers underneath. For the rest of the thinner, mineral spirits and naptha will work, but word is that "pure gum spirits of turpentine" (don't use turpentine that doesn't say that on the can) is best.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I've used Behlen Rockhard on 25+ guitars and never used the proprietary thinner… If I recall what's on the MSDS sheet it's no more than a mix of mineral spirits and naphtha at an increased price.
Hardware store turpentine (not a substitute) such as Ace or Kleanstrip works perfectly well, as well as naphtha. Naphtha flashes off faster, turpentine allows the varnish to flow a little more and gives it a different consistency that's better with a brush.

Most likely the excess of acetone made the varnish lift up, lacquer thinner would have the same effect. Acetone also allows the varnish to dry faster, it is something to take into account. I never add more than 10% in the gun, and that's plenty.

Rockhard is notorious for adhesion issues and requires a little more care in preparation. The common mistake is to thin it too much. Once the can is open it starts to polymerise, so a can of Bloxygen is a must. Once the varnish develops a skin it's good to throw out…

Sealing oily woods like the RWs, especially cocobolo, with a shellac or spirit varnish is highly recommended although the varnish will eventually dry after a week or so, depending on the environment (the warmer, the faster). I've sealed some guitars with Waterlox, it works well under Rockhard and helps the adhesion issue some, but doesn't solve it 100%.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

MSDS is a full listing of ALL! registered chemical compounds in a product regardless of health concern. Notice I did not say all chemicals components I said all registered chemical compounds They are not broken down by element IE hydrogen, nitrogen and so on but any compound such as methanol, either, hydrogensulfide, various glycols and so forth are listed. If a chemical compound is part of the products recipe it is required to be listed on the products MSDS.

You see you can’t leave off what is by its self considered safe compounds be cause when in solution or exposure with other compounds various reactions can accrue, change the required safety protection and or handling requirements. So be assured if it is in there it is listed in the MSDS.

Thanks for all the information. This happened on the top after I sealed w/ shellac and sanded with 320 grit and it happened on the second coat. I finished the back and sides and left the top for last, but it was two weeks later and yes there was a film on top in the can that I couldn't stir out, so I added acetone and ran it through a filter before brushing. I've sanded all the way back to bare wood and now I have to decide to either give up on the varnish idea and go back to my comfort zone and just french polish the thing or try it again with a NEW can of Behlen's. Oh what the hay, I should give it another shot! Thanks again! Clinton

Michael, manufacturers put what they want on the MSDS sheets. Possibly all dangerous compounds, but how is it monitored and how can we be sure?
I called a manufacturer last week (not Behlen) to ask what was in their varnish, namely what oil(s) and/or additional resin(s). They only had listed a couple of solvents and one resin on the MSDS sheet. The guy on the phone said it is proprietary and couldn't tell me.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

That is a hell of a good question. I know that there are products for various reason are exempt form MSDS requirments. I am not sure what exactly governs that. But those products requiring MSDS publication are required to list all chenical compounds. Now keep in mind it is possible to list a chemical compound for an organic oil that does not explisitly denote what orgaic oil it is, but gives the chemical compound make-up of that oil.

I do know that

When I used hardware store thinner in Rockhard I got a white precipitate in the can, and the varnish would not harden properly. Even though the proprietary stuff is more expensive, it's worth it to me to have something trustworthy.

I've had good luck using UV lights to speed up hardening time of Rockhard on oily woods. You MUST get the first coat fully cured before you put on the second, or the whole mess can strip off later. Once the first coat is 'dry' the subsequent ones should be ready for recoat in less than a day.

I only use about 5% acetone; just enough to bite into the previous coat a little, and thicken things up a bit as it flashes off. I'm brushing; if you want to spray you'll probably need more.

Don't use any varnish that has gelled in the can. Itis likely not to cure properly, and gels in the coating will make the surface uneven.

I use marbles to exclude air from the can. Just drop in enough to keep the level right at the top of the can. I started out buying a pint of varnish, and when the marbles got high enough in the can that I could not get the brush in, I got another pint. When that one got to full of marbles, I scooped out the marbles and dumped all the varnish into one can. Then I cleaned the other can out really well. Now I buy quarts, which are cheaper, and swap things back and forth as indicated. I clean off the marbles with cheap paint thinner and reuse them. I haven't had to throw out any varnish in several years.

Alan, was it "white spirits" that you used?
Turpentine, naphtha and mineral spirits all work as thinner for Rockhard (and possibly any oil varnish), or any combination of the three.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Ok- I completely sanded off the old finish and started over with a shellac sealer and got some turpentine and added 5-10% and WOW ! It worked great! Thank you all for your help. It looks and works SOO much better than I expected. Thank you all !
As far as MSDS, our safety director is constantly criticizing some manufacturers on how they write them. From what I understand any manufacturer that doesn't list all "hazardous" materials can be subject to heavy fines from OSHA. With all the chemicals we use, this is a great subject to investigate. Again, Thank you! Clinton

Laurent:
I don't know what that stuff is: the can says 'Paint Thinner'.

One problem with all such generic formulationsd (as opposed to things like acetone, that are what they are) is that the manufacturer can, and will, change the ingredients if something becomes hard to find or more expensive. One batch might work well, and the next might not. I've run into this any number of times over the years, with everything from denatured alcohol to epoxy. This is not to say that Behlen's might not alter the formula for their reducer, but they will, at least, see to it that it will work with the varnish.