Enamel gloss varnish?

Sound familiar too me I had the same problem with humbrol paints when I didn't let the color coat cure fully before clear coating. Humidity has also been known to do that to enamels also. Do you have a moisture trap in your ab line? Could be simple. Either case, you need to strip the paint and try again. No easy fix there I'm affraid.

Could you give more specifics about what you did, what paints you were using, and what the spraying conditions were?

Sure, I used Humbrol Matt Finnish thinned with turps and sprayed my model at normal pressure in my workshop which is warm but not humid.

I started with light coats and built up until a matt sheen covered the model. I'm wondering could I just have put too much paint on in one go? Tell me what you think.

Darren.

It sounds as if you may have built up the coating too rapidly. Turps (either turpentine or its substitute) is relatively slow to evaporate. When you apply several light coats in quick succession, microscopic solvent "bubbles" that have not reached the surface of the underlying coat may be trapped by the overlying coat. This condition worsens in either humid conditions or very warm conditions. If the ambient temperature is sufficiently warm, the surface of a coating may cure before all the solvent underneath can migrate to the surface and evaporate.

The easiest cure is to apply a light coat and wait to apply the next until the first is tack free. This is usually only about 15 to 30 minutes, at most, and often much less.

Another approach is to use a faster evaporating cosolvent (like toluene, xylene, or acetone) with your main solvent. However, this is an advanced—perhaps even expert—technique. It requires more experimenting with thinning ratios than most people care to do, and getting it wrong can ruin a nearly finished model.

Thanks for your insight on this one, I'll try more time between light coats.

Thanks,

Darren.

Hey Ross, not meaning to step on any toes here or anything...

But I've seen some funky results from time to time when another layer/coat of a material was applied over a finish that only flash dried and not cured. When we were spraying multi layers of clear over a fancy paintjob, the time was kind of critical. We had to get the next coat on while it was "just" tacky. If we missed the window and it was dry to the touch, we had to wait until it smelled dry so we would leave it in the paint booth with the heat lamps on all night. Once cured (sometimes a few days) wet sand and spray on.

Just my old body shops way of doing things. 

-- Edit --

uhm... not "my" body shop, just where I worked LOL.

Not at all, Jim!

Some coatings have a very specific recoat window—the label instructions usually specify it. Outside that window, recoating may produce very odd results. "Flash drying" is not the same as tack free, and is the proper term for some of what I described—when the outer surface is partially cured, but too much solvent remains trapped behind the paint skin. Most paint intended for the consumer market avoids the complication of a recoat window whenever possible—and I've never heard of a hobby paint that does so, thought I have not tried them all!

Thanks Ross

I'm not real sure of the technical aspects/terminology of what flash drying would really be, just that we called it when the surface dried while the underlying paint was still wet and leaching solvents.

Be careful with Testors spray enamels. Well they have a big enough window, recoat within 3 hours or after 48 hours. Unless you are building a really, really big model kit LOL.