Vallejo gloss varnish pebbly/grainy

VTmodeldude28

... But I'd like to get a glass smooth finish for F1 cars I build in the future....

That could be one answer to a glass smooth glossy finish--Future that is

I can relate to your problem, as I'm only a few months into airbrushing and the gloss coats are maddening! I'm having the same issue with Badger clear gloss, which tends to pool and puddle in a splotchy, sweaty fashion when I spray it straight from the bottle. It's already plenty thin, and it does come out like water all over the place. I had slightly better results with Tamiya gloss, but I'm still getting a pebbly/sweaty eggshell finish. Hopefully it's enough for decals and washes. But I'd like to get a glass smooth finish for F1 cars I build in the future.

The paint underneath is acrylic as well. It's not that it would be impossible to redo it, it's just black, not a camouflage-scheme or anything.

The "pebbles" are not just grainy when you trace the surface with a finger, like when the paint dries too fast from the airbrush, but really puddles, about 1-2 mm in size. If anything, it seems to me that the layer is too wet instead of too dry and the cohesion between the varnish is stronger than the adhesion towards the model surface.

Anyway, I've got some experimenting to do.

What sort of paint is underneath the gloss coat?  is it acrylic as well?  If not, you may be able to remove the gloss layer by using windex or acrylic thinner, but if it's an acrylic layer underneath, you'll remove everything.  Overspray would take a while, if it worked, and you would wind up with a very thick layer on top.  

As Don stated, if you're spraying from too far away, your atomized droplets could be drying in flight to the surface, and that could cause some of your pebbly finish.  I find several quick, light layers work best.  I read somewhere (I cannot remember where now) that about 5 seconds spray at a surface is adequate.  When I do aircraft, I try to follow this, as an example, spending 5 seconds or less over one upper wing surface, and constantly keeping the spray moving.

Hope that helps.

Follow-up question : how can I fix the current mess?

- overspray with clear until it's smooth again?

- very carefully sand it with some very fine grit? I have 600 to 1200 grit paper, but I probably need to go way finer?

Thanks for the reply, Don.

When I thinned it, it was roughly 60/40 (varnish/thinner), which I soon realized was way too thin. I think it's meant to be sprayed straight from the bottle though.

I've been experimenting with it several tries and sometimes I thin something to get it finally spraying, while actually there's a different reason the paint isn't flowing and I've thinned it way too much.

I can't tell which pressure it's at. I have a rather cheap Revell airbrush starter kit. It has a little blue compressor with 3 settings (High, Medium, Low).

I've only been airbrushing for 2 months now (max 1 hour per week), so much yet to learn about pressure and thinning. I know enough already to realize that just about every brand, colour, primer or varnish will have it's own "sweet spot".

I will try the varnish again at lower pressure.

Pebbly f inish is usually caused by too high a pressure or holding airbrush too far from surface.  What pressure are you using?  Also, when you tried thinning it, what ratio did you use?  It sounds like you just thinned it too much.  You do not need to thin accurately to a percent or so, but you probably need to be within about 20%.  There is a unique set of thinning ratio, pressure, and distance to get good results.  You need to find that sweet spot by testing and practice.