Painting urethane plastic, any advice?

Hi there,

I wanting to paint a urethane plastic, Model TARDIS.

I've not used mold release, but i'm having troubles with the primer.

A lot of advice i've read, say that the paint just pools on the surface of urethane, but that's not happening with me.

On the tests i've done, the paint either goes on, but doesn't dry, or more importantly it does dry, but scratches off very easily.

Is the scratching off normal?

thanks

Richard

strip it,and use a primer.

I’ve made some helmets out of polyurethane and a very smooth film is left on the outside of any castings. You need to rub this off with sandpaper so it is not shiny or smooth anymore. It should look dull and the rougher the better then primer it. After primer sand again with smoother sandpaper and if you can see the scratches put another coat of primer on and so on.

There's a product called Tie Bond by Matthews wich is an adhesion promoter.
It has to be sprayed on with an HVLP gun.

just sand it down like 3phase said making sure not to take away any of the details. You need to do this in order for the primer to stick. I've had this problem when I painted urethane for the first time. It never dried or paint came off when I masked off an area lol

you can also try dipping in acetone for about 20 seconds. we used to use it when i worked for a sculpting firm. but it's very inflammable.

Try giving it a soak in Westley's Bleche-Wite tire cleaner. This stuff will remove anything that may be on the surface and allow the primer to adhere properly.

After soaking, you can also give it a light scuffing with a scotch-brite pad, to give the primer something to really bite into.

And as for the paint, you may want to go with an enamel or automotive lacquer. Just try the lacquer on a small area of the bottom, first. Some lacquers are hot and can screw with some urethanes, so be careful.

-Fred

halfords sell plastic primer for car bumpers and flexible plastic in spray cans.use this after using CifF (used to be jiff) and a little water with an old toothbrush to remove any grease and molding agent

I've heard that putting baby powder in the mold before casting will result in a surface that is easier to paint. Any truth there?

With my IG-88 heads, I do a light sanding then spray on primer. Works fine from there.

Scott

For my resin castings I used dish washing machine detergent and hot water. Soak and then scrub with an old toothbrush. I tried dipping them in acetone- it definitely removed the release, but it also warped the parts and they became soft and rubbery, permanently. I use Mr. Surfacer to prime, it is lacquer based and gets a pretty good bite on the urethane.
I'm sure sanding or scuffing with Scotchbrite would work great, but that wouldn't have worked for my castings- too small and detailed to be sanded.