Degassing

Thanks all!  That's what I suspected it was.  It also explains the mess I had the other day.  I had decanted the primer into a large air brush jar, closed it and set it aside.  Next time i opened the jar the paint had of course settled.  I whipped out my trusty new Micro-Mark paint mixer and started stirring.  Well, eruption is a tame description of what happened next.  The paint came gushing out, all over the jar, the paint booth, my hands and the new paint mixer. I'm not kidding, the mixer was covered up to the switch and I thought I had ruined it.  Luckily, it came clean as did me and the booth.  Oh well, lesson learned!

Thanks again!!!

I had to decant a bit of spray can primer to do a little brush work lately.  The can was "red oxide" primer, just what I needed for the floor pan of a model but had to touch up some spots where I had to hack with knife to mount floor pan.

I first just sprayed into plastic drinking cup.  Was able to touch up with a small brush, but the bottom of the cup melted out and got paint on bench top.

Then, needed some more.  This time I used a paper drinking cup.  Worked great!

I wondered about this myself a while back and decided to experiment with it.

I decanted a primer into one of those little glass jars from Testors. I let it sit for a little while, but only after 5 minutes or so I screwed the lid on. I let it sit for a few more minutes then removed the lid and heard the gas release. I then put the lid back on and shook it up, the took the lid off and even more gas released. Finally, I left the lid off and stirred the paint with a bamboo skewer or toothpick or something and the paint pretty much exploded all over my hand. I was startled that it had reacted so violently. But, now I know first hand that you actually do have to let the paint gas out before use.

I always feel better after de-gassing...

Universally, spray paints (in the can) consist of a mixture of paint and liquid propellant. The propellant is usually a low-boiling point hydrocarbon. When you spray paint out of the can, some of this propellant comes with it. When actually painting, you are applying a thin layer and the propellant disperses quickly. However, when you spray it into a container when decanting, it can take considerably longer for this propellant to disperse..

De-gassing sinply means leaving the decanted paint for a period of time to allow the propellant to escape.  This can only occur in an open/loosely covered container. If the container is completely sealed, as the gas escapes, it will pressurise the container and this pressure will prevent further gases from escaping from the paint.

The primer will still contain propellant from the can & this needs time to evaporate.

Having primed a 1/72 winged blob of resin & a 1/24th scale car last night with a rattle can, overspraying a wall, a dustbin & my hand, I can see the attraction of decanting!

Vallejo have a new Polyeurathane airbrushable primer but I haven't got my hands on any yet.