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I noticed there was some interest in Behelen's rock hard varnish in another thread, so I am hoping those of us who use it can pool our knowledge to get a good finish schedule for this stuff.
I'll tell you what I do and the problems I have and maybe someone can chip in with a solution they have found.
I just finished two guitars, and I used zpoxy finsh resin for pore filling on the back and sides, and shellac as a sealer on the top.
I used Alan's thinning formula - twenty percent rock hard reducer ( mineral spirits would work as well), five percent acetone to help a little with burn in, and a few drops of kerosene per pint to help flow out. This bruses out really well with no brush marks just using a brown nylon brush from an art supply store.
The problem I have is what looks like fine sand in the finish. I run my air cleaner for hours before varnishing, strain the varnish for each coat through a coffee filter, vaccum the guitar, then wipe it with a clean cloth and then a tack cloth. I clean the brush multiple times in thinner and then in soapy water. But as soon as I start varnishing, I see this fine grit in the film. I have the varnish in a clear plastic cup and when I hold it up to the light I can't see anything in it, but as soon as I start putting it on the guitar it's everywhere. If anyone knows where this is comming from I would love to hear it.
The good news is that it seems to come to the surface as the coat dries, so I can sand it off with 400 paper between coats. But it would take a lot less sanding if I could eliminate this to begin with.
This finish looks so great I think it will be worth the effort to figure out. It has a warm amber tone and glow that nothing else matches, imhop. I finish it with micro mesh and compound on the foam pads from StewMac.
Any information you have on the process would be apprreciated.
                      Thanks, Paul Harrellpaul harrell38760.017349537

Sounds like something is contaminating the varnish, perhaps in the brush itself. What do you use the clean the brush? There may be traces of whatever it is left in it, and this causes a small reaction with the varnish, causing little micro-balls of sort.

Have you tried a different brush? Have you tried a natural bristle brush? A badger brush? Have you tried a different container? Different thinner(s)? Different brand of thinner(s)? Spraying?

Little problems like this usually require you to look at everything along the trail in order to find the culprit, and it will likley be something you never would have guessed.

Are you sure they're particles? Could they be air bubbles?

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JJ
Napa, CA
http://www.DonohueGuitars.com

I have seen similar on my brush while cleaning but I haven't noticed it in the finish. I have also started spraying the varnish and this gives me the best finish so far.

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

Hi Paul,

Just a stab in the dark here but could it be the acetone de-gassing from the varnish when the thin wet coat is layered on causing small craters on the surface and preventing the finish from levelling correctly?

Just a thought rising, feel free to shoot it down if it sounds ridiculous.

Kim

I found this thread in the archives with a post by Alan Carruth about varnish.

Varnish Info

It has some good info in it.

Might be a contaminant in the tack cloth. Some people make their own
tack cloth with the same varnish they use and a turpentine-soaked/
wringed dry rag.

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

What about tempature? And humidity? What's the weather like in your location? And what's recommended by the mfg?

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Chris Nielsen
Soquel, CA.

Cumpiano has the "Haselbacher" Rockhard regimen on his website in his articles. Ilooked real hard at this bacause it had great similarity to the gunstock Tru-Oil finishing process I am already comfortable with. I find the acetone for off-gassing in your way interesting,but, I am always leery of mixing my solvents when finishing.

It is definitly some kind of particle, not air bubbles, you can feel it in the dried coat. Like Mario I suspected the brush, but I have used badger, china bristle and now nylon. I don't know how I could clean it any more; I use lots of the rock hard reducer and have tried soap and water after that but nothing seems to help
The temp in my shop is 68 to 70 with 40% rh when I'm finishing.
It was much better on the first coat when I was going over the zpoxy - didn't see much then
It may be sanding residue that I'm not getting off the guitar before recoating, but I'm wiping with several clean cloths and then a tack cloth. What are others doing to remove sanding dust before recoating?

That's 'sand'! That's what they call the little specs of hardened varnish that you just can't get out of the brush. You can never eliminate that entirely, but you can minimise it.

I had a student who is an artist and art teacher, and she told me how she cleans her $200 sable brush: soap and water. Lots of soap and water. I use a Chinese bristle brush that didn't cost nearly that much, but that's how I clean it now.

Actually, you have to go back a couple of steps to where you're varnishing to do a good job cleaning the brush. _Never_ get varnish up into the metal ferrule of the brush. Once you do, you'll never get it out, and it will just shed 'sand' into the brush forever. I am careful never to wet more than about 1/3 of the visible part of the bristles with varnish as I work. If you can't cover the surface fast enough with that amount on the brush, get a wider brush. I find the hardware store ones perfectly adequate, and they get better with age, as they soften up and develop more 'flagging' on the ends of the bristles.

I clean the brush fist by squeezing as much varnish out as possible, working from the ferrule to the tip. Once I've done that I dip just the tip into a small container of thinner, and squeeze that out the same way. _Don't_ swish the brush around in the thinner: that just contaminates the thinner, and carries varnish up the brush into the ferrule. After a number of dip and squeeze cycles, when I have gotten most of the varnish out of the brush, and dried it as much as possible with a paper towel, I wash it.

I use Ivory soap and lots of warm water. Run water into the brush back at the ferrule, and soap it up. You may get some really disgusting snotty stuff at first: use more thinner next time. The soap reacts with any leftover oil, converting that to soap, which you then rinse out of the brush. Be sure to work soap all the way up into the ferrule, and rinse it out completely. Soap, rinse, repeat, until you can work up a nice lather all through the brush with only a little soap. Dry the brush out with a paper towel and let it dry completely before you try to use it again. I have two brushes, so that I can apply varnish twice in one day.

Before you use the brush, flick or fan the bristles several times to dislodge as much of the 'sand' as you can. If you do this in the light you can see the 'sand' coming out of the brush, and you'll have some idea how much there is. Lots, I suspect.

I've found this schedule is the only one that works for me. It's a drag: it takes longer to clean the brush than it does to varnish the guitar, but it works. I tried the business of suspending brushes in thinner, and ended up with petrified brushes. I can't get all the varnish out without soap; again, they just petrify. I used to get about one guitar out of a brush, which is a drag. I've been using the same two brushes now for more than five years, iirc.   

Once again, I am blown away by how unbelievably lucky we are to have Al Carruth on this forum!!! The guy is a bottomless pit of helpful information, and his generosity in sharing it is astounding. I think we should all go to Al's house and clean his shop, wash his dishes, do his laundry, change the oil in his car...

THANKS, Al!!!!

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Alan - thanks so much for taking the time to reply. Now I realize why the first coat didn't have the sand that the rest of the coats did - the brush was new. I've been getting varnish and lots of thinner in the ferrule when I clean it out so I guess there is no mystery where the sand is comming from.
I have been spending about an hour per coat sanding before recoating- almost level sanding between coats to get rid of all the sand. Thanks again for helping me solve this because I really love the way varnish looks on the guitars I've done so far, I just need to get faster at it.

                   Paul Harrell

Most of the finishing experts I've read say the first step in brushing should be to dip your brush into the appropriate solvent for your finish, all the way up to the ferrule, then remove the excess so it doesn't dilute your finish. That way, any finish that wicks its way up toward the ferrule (and it always seems to) won't have a chance to harden before you can clean your brush. Otherwise, Alan's advice is "by the book," and, as usual, can't be beat!