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John TenEyck
04-05-2013, 12:46 PM
I've sprayed toners made with shellac + Transtint dyes many times w/o undue problems. However, on my latest project the sprayed film wants to separate, for lack of a better word, into little circles with less toner in the center and more around the edges. It's not fisheyes and I can't see any change in film thickness at the center. The finish looks like what happens when a light rain shower hits the hood or roof of a dusty car. It doesn't happen with the first coat, but does with subsequent coats. I can minimize it by spraying coats of minimal coverage, but I can't really eliminate it. No oil/water in the air, fresh can of amber shellac and new gallon of DNA. I know, shellac in the can has wax in it, but I've used the same stuff at least half a dozen times before w/o this happening. Any ideas?

Thanks,

John

Prashun Patel
04-05-2013, 1:15 PM
John-
I had this issue when spraying straight transtint (Antique maple) in DNA onto maple plywood panels. I switched solvents to a faster drying one and diluted the dye even further. That solved it for me. Perhaps either of these will help you?

John TenEyck
04-05-2013, 3:57 PM
Thanks Prashun. What solvent is faster drying than DNA that is compatible with Shellac?

John

Prashun Patel
04-05-2013, 4:22 PM
Maybe I was misleading; I meant I used a faster drying solvent (50/50 ethanol + acetone) when spraying the dye only; I was not spraying toner. IMHO, the bigger factor for me was thinning the dye.

Mark Kornell
04-06-2013, 12:56 AM
John,

To answer that question - methanol flashes faster than ethanol (DNA). Shellac takes longer to dissolve in methanol, but I've found that grinding it in an old coffee grinder works wonders. Coarse grind, mind you - an espresso grind gums up the grinder :-)

If you go that route - and I don't think you need to - you need to make sure you're not breathing in methanol fumes. Ethanol fumes will just make you happy, methanol fumes can cause blindness :-) A spray booth with excellent airflow is pretty much mandatory if you use methanol. The only reason I use it is because here in Canada, methanol is much easier to find and far cheaper than ethanol.

To answer your original question - I've had the same problem using shellac and dye. I traced it to using too little air pressure. Try dialing in a bit more psi. With my gun (Iwata LPH-400 LVLP with 1.2mm N/N), I found there was a pretty fine line between having way too overspray and getting that mottled, leopard-like look. I've taken to always spraying test panels to dial in the air pressure by 0.5 psi increments. I'm using a pretty beefy air compressor so supply consistency isn't an issue, but that's something you might need to consider.

Also, I need to state the obvious, and tell you to make sure your gun is really, really clean.

John TenEyck
04-06-2013, 10:54 AM
Thanks for the input. You could be right about the air pressure, but I'm not sure. I had sprayed the panels with a basecoat of 50/50 Sealcoat/DNA. When I sprayed my toner coat on top of that, that's when the problem occurred, but only on the second and subsequent coats. Today I sprayed a panel with no basecoat, just the toner. Two, three, four coats - no problem. I did turn up the air pressure yesterday when I was working on the problem, so it's not clear which change was most responsible. I'll have to go try each separately to find the root cause.

John

Alan Lightstone
04-07-2013, 1:27 PM
Has methanol vanished from the US? A few years I tried to find some to mix up my own windshield washing solution for the cars, and no one stocks it. DNA seems to be everywhere, but no methanol in the borgs.