I am about at my wit's end: whenever I add a clear flat acryllic topcoat prior to weathering, I seem to pick up whitish blotches, almost like salt stains. If I apply a pinwash made with white spirit/mineral spirits, it will reduce the problem in some areas, but overall it's very had to get rid of.

Am I doing something wrong?

I dilute the clear coat with 50% distilled water and spray it on.

What kind of clear acrylic are you using? It sounds to me like the clear and H2O aren't mixing well. Try the manufacturers recommended thinner instead and see if it solves the problem.

I got this 'effect' when i'm using Mr Color Super Flat coat.... but i discovered the trick to eliminate this whitish is by applying a thin layer and leave it for a few minutes then apply another layer.
Dont apply to many heavy coat at one time...

I noticed you used water base coat, i believe it's the same....

hope this help

Polly Scale, which most think is the best. It's water-soluable.

I had a similar problem with Vallejo flat varnish. I stopped using distilled water to thin, and used the Vallejo acrylic thinner instead. That seemed to do the trick for me.

I have never used Polly Scale, but I had a similar experience with Gunze clear flat, and the problem could be solved by using Mr Color thinner. So I guess it is a good idea to use the factory recommended thinner.

Concerning the white spots, I could remove them by gently brushing through the surface with an alcohol or thinner-dampened (not wet) flat brush, try this first however. This process leaves brush streaks, which may make a second flat coat and some sanding with very fine paper necessary.

Hope it helps.

I believe that it could be caused by spraying too much on the same area. Using water, it takes longer to dry, so spraying over the same areas the amount of flat may accumulate. As already recommended, use a better thinner (which also ixes better) or spray lighter coats and leave some drying time in between.
Spraying too much of any flat coat will see a build up of this whiteness ... the model wont get "flatter".

I find that with any clear, flat or gloss, problems with air pressure (too high) or thinners (too hot) can cause an over-spray / orance peel like effect that results in a frosty or whitish finish (often in corners and undercuts). The atomized clear coat drying (even partially) before it lands on the model sometimes creates microscopic clear "balls" or "beads" that look white.

So, air brush set-up might be worth looking at as well as a possible thinner-clear finish compatability issue.

I will try lowering the air pressure and using an acrylic thinner. Thanks, gents, for the advice.

Bill, I had the same problem recently using Polyscale. Mine resulted from 2 things - old paint and air pressure too high. So, I got a fresh bottle of paint and lowered the pressure a little and now everythings marvelous.

Bill;

Hi.

IF you are using Polly-Scale Model Railroad Colors clear flat - please be very cautious about using any "acrylic thinner" in it!

I don't have this clear flat stuff, but all my other Polly-Scale paints say to thin with distilled water - up to 15% only. I have found by bitter experience that adding alcohols, such as I do to my Tamiya acryls for AB use, really screwed things up! The paint sort of "gelled" and clogged up my AB.

So, "acrylic thinner" maybe should be avoided for this specific brand of paints, as various of these thinning cocktails do contain one or another alcohol.. I would also avoid the windshield-washer stuff with these P-S paints, as that contains alcohols, too. Now, of course, if you have some sort of "Polly-Scale" thinner... That should be OK!

I think your problem may well have been "thinned too much", if you added 50% water? Again, my P-S bottles all say "reduce 10 to 15% with distilled water". Other than that, I think the previous posts saying "use thinner coats with drying between" are spot-on.

Good Luck!

Bob

I had this problem last summer too. I tried thinning with water, which didn't help. Also tried thinning with Isopropyl alcohol which helped slightly. In the end it turned out to be atmospheric conditions that were my problem. It gets pretty hot here in New Mexico in the summer and when airbrushing in the afternoon, I pretty much always got this problem. When airbrushing later in the evening or early in the morning, I had no problem at all. So could extremes of heat or cold (more likely at this time of year perhaps) be a possible cause?

Bill,

I had exactly the same problem with PS Flat Finish. The solution was three-part:

1) old paint - replaced with a fresh bottle

2) stir it very well, as the contents can settle - the first few uses are fine but what is left won't work

3) spray on in very light coats with at least 10min drying time between them. If hand brushing, get it very thin - anything "built up" in crevices will cloud up.

Despite being temperamental it's still the best flat finish I've found.

Tom

Well, it's very cold in my basement, so that may be a problem.

I'm going to dial back the air pressure.

I'm going to thin it less.

Hopefully that will solve the problem. Thank you all for your help.

i had this problem as well. i used a MM lacquer clear coat. dont remember what i used to thin it. i would imagine i used normal thinner, but not possitive. if it leaves a white film over the entire model, i would say it could be a couple things. number one culprit that comes to my mind is an unpure clear coat. IE: dirty thinner. excess moisture may even cause something like that. heck, even a bad drying environment, trapped air, etc
for me, my white spots were on my hummel where the body met the fender. so, im pretty sure my culprit was excess clear coat gathering and drying in one spot.

Gents, lowering the pressure and thinning it less seems to have tamed the beast.

But if PS flat is the best, what are we going to do? They've discontinued it.

I used to use the testors dullcote, but I have to say I have been very pleased with the Vallejo matte varnish (once I figured out how to thin it correctly).

I have the similar problem too. Then I realise, if I spray it during a warm wheather it do not give this problem but when it is raining or the wheather is cold then this will happen. I hope tis will help you.