does paintin/brushing resin is foaming?

[Drachenklinge]

Hi there,

having not much experience with resin, I may need a little advice. Right now I am painting some equipment, markers and mission-targets ... all made of resin. I cleaned the brush, changed the brush (most with natural hairs*), changed the water, cleaned the cup, am using different colours (however, all Vallejo). Still it always begins to produce a bit foam at least. Meaning, there are some smallest air-bubbles. The only way seem to be using pure colour without water (that's why I used absolutely fresh water out of the tap as a test, to the same outcome) which is too thick, so I'd like to avoid it.

I thought it might got something to do with some sort of micro-surface-effect, similar to ceramic ... 

Am at a loss, here. Help or answers appreciated
DK

* not mine, though 

[zizi666]

Did you rince the resin parts ?
Always put resin in a dishwash solution to get rid of the oils on the surface or else the paint won't adhere to the surface.
(I've had resin pieces that still were greasy even after days in a dishwater mix)
After that it's just priming and painting as usual.

[Drachenklinge]

nope, no rincing, thanks for mentioning. I know that part, but use it very very seldomly. Maybe, with resin, it is more important?

And that's what bugging me, since I didn't do anything else than usual - and it never foams. Not even that much, when I forgot to clean my brush after using wood-glue and/or soap.

DK

[Connectamabob]

Washing resin before painting is important because the resin can have mold release or oils from the mold rubber left on the surface, which can cause paint adhesion problems. Not as essential with metal or plastic (though still a good idea), but with resin you always want to wash the parts. It has to do with the types of molds and casting processes used: the processes/materials used for resin are much more likely to leave residue on the model's surface.

Usually residual oils or mold releases just causes paint not to adhere properly (peeling/flaking off after dry, or beading up while wet), but if whoever cast this particular stuff used a surfactant somewhere, that might cause paint to foam when brushed.

Another possibility is "pinhole" air bubbles in the surface of the resin itself. This can happen if the resin was mixed too vigorously and/or improperly degassed (or not degassed at all). The resulting casting is riddled with bubbles, and tiny ones that abut the surface form little "pinholes" in the final casting which can wreak havoc with paints. When the paint goes on wet, surface tension causes it to get caught at the edges of the pinholes instead of filling or skinning over them, making them much, much more visible then they were on the unpainted resin. Dense or large clusters of pinholes can have a foam-like appearance when revealed by paint, as well as being more likely to case actual foaming due to mechanical agitation when brushing (imagine trying to paint dry coral with a brush).

The fix for pinhole bubbles is to sand the resin lightly to open up the pinholes, then "spackle" by brushing on thickened primer or solvent based putty, and carefully wiping with a solvent-dampened tissue.

[Drachenklinge]

thanks to both answers, folkes. Need to pay more attention to prepare the resin in the future, then. Right now it is too late for most of it, but some equipment is still left, so I will try that and compare.

Thanks again
DK