I only have run into this with helicopter rotors, every one of them. I’ve tried lightly sanding with only slight improvement. You can see the variation in texture, and sheen on the plastic. I can’t sand more or I’ll start destroying panel lines. I don’t know what causes this during molding and am at a loss.
If you look at the picture please note that it all black but the smoother parts look darker. This was after a failed attempt, stripping, sanding and respraying
Is this defect in the bare plastic or flaw in paint ?
You can see an anomaly in the plastic. Had the same thing with three other helicopters by various manufacturers. The plastic is smooth as glass but when you paint it it goes haywire.
Is there primer or just topcoat?
Which type of paint or primer are you using?
I have seen something similar when I painted styrene with cellulose laquer (it used acetone as solvent …).
The surface looked like scaled down vinyl afterwards, it was the targa roof hatches on a Corvette so I wasn’t all that unhappy about the result
No primer. I’ve used two different rustoleam blacks with the same results. Gonna hit one with dull coat and see if anything changes. Naturally the rougher parts look lighter .
Are you spraying perpendicular to the top and bottom surfaces of the rotor blade?
If you are spraying at the leading edge , remember this is an airfoil and doing so will
create regions of pressure differential between the top and bottom surfaces with it’s attendant effect on how the paint lies .
I might suggest that you try hobby paints and thinners that are specific for plastic models .
Rust oleum paints likely have solvents that may be too strong for styrene.
I ended up going over them with steel wool and oil and pretty much resolved it. You may have a point about the paint though. I noticed today after they sat a few days that mineral spirits was about useless for removing paint at glue points yet I can remove testors OD in a second even after weeks.
Tamiya gray primer as a base may have prevented this problem. I think the Rustoleam solvents are migrating because the plastic is so smooth that the paint has nothing to adhere “bite” into because there is no primer. You can strip the paint, spray it with primer, and then repaint it with Rustoleam.
Rust-Oleum enamel sprays are no longer just oil based, they are trying to mimic traditional solvent based lacquers, and often they will call them lacquers. They are just oil based enamels thinned with solvents. They smell like lacquer, they almost dry like lacquer but they run like enamel and while they dry to the touch like lacquer they take longer to cure because the oil base is still present. The way you know Rust-Oleum isn’t lacquer is by the recoat times, if it mentions anything about “after 48 hours” then it is oil based for sure.
The problem is that the solvent can still harm the plastic. I have airbrushed red doll eyes for my wife when she crocheted a couple of Mothman dolls and I used Rust-Oleum canned paint from the hardware store thinned with acetone, it worked great and dried fairly quickly but the fist eye had a run and wiping off the paint revealed it was softening the plastic.
I chose acetone because I have always found Rust-Oleum and testors gloss red and silver to be very slow drying to the point of leaving finger prints in the finish weeks after painting.
Airbrushing is a much better application method than spray cans. There are cordless airbrush kits on the market that will beat a spray can even with the two dollar included airbrush. In my spray can days I dreaded paint day, now the airbrush sits on the bench ready to go and I have to keep myself from deploying it too early. Water based paints are so much more forgiving, no harmful fumes while curing and a breeze to clean up. Many brands of hobby acrylic are thinned for direct airbrushing and others like Tamiya can be thinned by the jar after purchase, this results in less waste. I do recommend a filtered booth that vents to the outdoors. Just because it’s safe to touch or ingest doesn’t mean it’s safe to inhale. Things can go sideways when you aerosolize liquids and honestly it’s not easy finding out what is in the paints and thinners.
Yes it does say repost after 48 hours. I guess what I can’t understand is why if it’s something in the paint why it’s so selective. Many areas show almost zero issues while others do and even change texture.
