What to use to fill imperfections in urethane castings

[Makrel Johnson]

I'm pulling a couple 1st gen casting from a mold made from a clay master and the clay has some very minor imperfections in it that would be easier to correct in a descendant pull and then re-mold. I have some polyester filler and some of the bondo brand spot putty but I'm not 100% sure if they'll adhere or cause a reaction.

Any suggestions for touching up a small bubble here or a ripple there?

I did spray the mold with a light coat of primer prior to pouring to 'encourage' adhesion but before I try a few things and waste some time, I thought I'd pop a question to the brain-pool...

Thanks!
Mak

 

[Sigma-LS]

Everybody uses bondo spot putty as the standard go-to for building resin kits. Works great, and way cheaper than tamiya.

But that's spots and scratches and stuff. Anything more substantial and you'll want some kind of epoxy putty like milliput to do the job.

Here's proof, made this guy myself out of Smoothcast 310.

 

[Propsjonnyb]

Any form of epoxy putty or adhesive will do , even car body filler ( bondo/ P38) at a pinch , just use a little and once dry sand smooth with medium and fine grit sandpaper , prime and then paint , you can get cans of plastic filler at car body repairs shops , this can also be used but with a very light touch.

 

[RickDTM]

Small air bubbles can also be filled w/ superglue. Fill the bubble, apply kicker, then sand smooth after the glue sets (almost immediately). The glue sands ultra smooth and is a fast way to fill a bubble.

 

[NormanF]

Everybody uses bondo spot putty as the standard go-to for building resin kits. Works great, and way cheaper than tamiya.

I used the red stuff to fix some serious problems I had with a part I was casting in SmoothCast 65D and I did like Mak is saying: I fixed the problems and made a new mold from that. There are still problems, but it looks ok.

This is it before primer and making a second mold:

 

[Makrel Johnson]

Thanks - I like the superglue idea, I have sanded the surface well enough and done a primer guide coat and there's still a handful of .05 (like mechanical pencil lead) bubbles here and there. I like the surgical approach versus the slather and sand but I saw where that's good for leveling the nigh imperceptible ripples from clay rakes on hard NSP.

...Of course they're pretty damn perceptible once you pull a cast :|