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Mitch K

Spraying varnish - issues

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I've never had any problems with spraying the two varnishes I use, until just recently.

I use Klear, not thinned, with about 1% W&N acrylic flow improver as the base coat/gloss coat. For the matt, I use W&N Galeria, mixed 3:1 with Liquitex airbrush medium and about 1% flow improver.

I'm running an H&S Ultra with a 0.2mm needle/nozzle, at about 12-15 psi.

What was working flawlessly now gives two different issues:

The Klear, rather than laying on as a uniform layer, now "beads" and will not form a layer except with a very heavy application.

The matt gives a horrible "orange peel" finish.

I've discarded the mixes, and prepared fresh ones, with the same result, checked the water/oil traps and inline filters on the air supply (all fine).

The mixes are prepared from the same stock materials I used that worked, so I'm at a bit of a loss.

The only thing I can think of is a temperature issue: I spray in my garage, so it's at ambient temperature. I've had issues in the past getting blooms when I've sprayed solvent-based paints under these conditions, but I've found acrylics to be much more forgiving.

Can anyone point out what obvious thing I'm missing, before I grind my teeth down to stumps?!

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I use Klear as well, unthinned. The only thing I check for is that it's not drying around the needle tip. I've found if it does even in the slightest then it affects the spraying producing a somewhat rough or it 'blobs' out. I've learned that from bitter experience.

I use Humbrol for Matt heavily thinned with good quality white spirit, my favourite brand being Bartoline. Between layers for both Klear and Matt I use a hair dryer to speed up the drying; only takes a few seconds.

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Never had this problem with the W&N matt, I thin it with Tamiya X20A with nothing else added and spray with a fairly high pressure not too close and it seems to dry/level out nicely, not as you described, although I do use a .3 needle.

I have had Alclad aqua varnish do as your Klear so tend to put a very light coat over the model first and allow to dry then go over with a heaver coats, seems to give it something to bite too and prevent the pooling/beading

also I use multiple coats to build the gloss up.I've fallen into the 'I'll give it a heavy coat to get a good gloss in one hit' and regretted it

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I use Klear, not thinned, with about 1% W&N acrylic flow improver as the base coat/gloss coat. For the matt, I use W&N Galeria, mixed 3:1 with Liquitex airbrush medium and about 1% flow improver.

blimey, I just thin mine with water....

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The mixes are a result of experiments and finding what has worked well. Besides, I'm a chemist and that sort of thing is through me like the letters in a stick of rock!

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Is the base color the same as before, I have found especially with Tamiy acrylic that the first couple of coats of clearcoat just sink into the basecoat. were as with enamels etc a sheen can be built up with a lot less.

Orange peel can be caused by low pressure.

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Cheers guys. I'm going to try a bit of heat, a slightly higher pressure (~20psi or so) and thinner coats.

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There is a drop of pressure in the air hose between the regulator and the airbrush depending how long it is. It occured to me last night that would also a drop in temperature also affect this. i had a problem with my H&S where there didnt seem to be enough air coming out of the brush even with the pressure turned up, I took the air valve apart and gave it a good clean and it was right as rain.

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There is a drop of pressure in the air hose between the regulator and the airbrush depending how long it is. It occured to me last night that would also a drop in temperature also affect this. i had a problem with my H&S where there didnt seem to be enough air coming out of the brush even with the pressure turned up, I took the air valve apart and gave it a good clean and it was right as rain.

Good point. My regulator is about one metre from the airbrush (I have a primary regulator on the compressor and a second one on the filter/trap which is on the spraybooth.

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same problem with Klear. it beads up. trick is to spray light coatings, then, spray heavy, close and quickly.

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I use a psi of 5-6 for airbrushing on Humbrol Clear.

Admittedly, I have not yet figured out how to best get the perfect gloss coat end result.

Edited by Housesparrow

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How old is the bottle of klear? and how many times has it been open, I has similar problems, then I bought a new bottle and noticed how foggy looking the klear was in the old bottle, when compared side by side to the new one, might be the klear has started to harden off in the bottle.

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This might be a bit long.

I THINK I've solved the problem.

I prepared a fresh mix, and hit an old kit - orange peel!

Tried it again the next day when it was warmer - worked!

I suspect the problem is that at a low ambient temperature, the extra cooling from expansion of the compressed air causes pushes the varnishes past a critical point at which it fails to spread and level properly.

By warming the varnish, airbrush and subject, the problem goes away.

I've also tried adding 10% isopropanol to the mix, successfully, presumably by lowering the critical temperature via an anti-freeze effect, as well as reducing the effect of any residual oiliness from dirt washes.

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All of this probably wasn't helped by an airbrush fault. I found that there is a (literally) microscopic crack running the length of the nozzle. Under a x10 lens you can see something but it isn't clear what, but setting the thing up on a dissection microscope in the lab at about x30 it's clear that there's a hairline split there. Replacement ordered, which hopefully will help.

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