Sanding Plastic

[G-Man]

When sanding gaps, scratches, or whatever on the actual model plastic, what grit do you finish at? I've just run into an issue where my primer isn't sticking to the model where I repaired a gap. It won't feather out, the primer just keeps chipping off when sanded. So what grit do I stop at that will hold the paint and be filled by the primer?

[CANicoll]

What primer are you using and what are you using to fill the gap - first question is has it fully dried before you primed it?  I've had problems with Vallejo Plastic Putty not feathering very well (I either don't let it dry long enough or I'm letting it dry far too long), but Squadron White putty feathers very nicely after its dried.

Good luck!

Chris

[G-Man]

15 hours ago, CANicoll said:

What primer are you using and what are you using to fill the gap - first question is has it fully dried before you primed it?  I've had problems with Vallejo Plastic Putty not feathering very well (I either don't let it dry long enough or I'm letting it dry far too long), but Squadron White putty feathers very nicely after its dried.

Good luck!

Chris

I'm using Mr. Surfacer 1200 as primer. I used super glue to fill a join line, so no putty was present. I let the glue dry a day before sanding on it and I finished sanding with 12000. Then primed several days later. I'm thinking maybe I don't need to finish in 12000, just not sure what grit I can stop at.

[Gazzas]

1200 grit should be fine enough for most stuff, mate. 

[CANicoll]

G-Man - I'm really at a loss why your primer (Mr. Surfacer) isn't  sanding well.  Esp over a CA seam.  That is just not making any sense to me.  I have not had problems like that with 500 or 1200.   What grit sandpaper are you using?  

 

Chris

[D.B. Andrus]

G-Man

 

I agree with Gazzas - 1200 grit is more than enough and that's giving a mighty smooth surface. Are you going for a gloss finish?

 

Cheers,

 

D.B.

[A-10LOADER]

 12000 prior to priming, that's your problem right there. The surface is too polished for primer to stick. That would be like putting wax on your car then, trying to paint over it, it just wouldn't stick.

320 or 400  for sanding the body work then primer.. If you hit the CA with accelerator, you can sand right away and save a lot of time. 400 wet sanded prior to paint. I've never had an adhesion problem doing things this way.

 

Steve

Edited August 20, 2018 by A-10LOADER

[ScottsGT]

Yep.  Too slick!   Many years ago I took an apprentice position in a body shop.  I knew a little, not enough to know when I'm being set up.  Had a friend that brought is Camaro in after an accident because the shop had a reputation as a custom house.  Bodywork was done, and friend showed up measuring all door gaps with match sticks.  This pissed the shop owner off.  When he handed me the car to paint, he instructed me to prep with a final sand of 800 grit before I laid on the custom lacquer base colors.  I should have known something was up because of his insistence of the 800 grit.  But hey, what did I know?  I was still in school for this stuff and everyone was spraying polyurethanes during that time. 

About the time the car was done, the shop owner split town.  Left his wife and kid and took a bunch of investors money and went back to CA supposedly.  He could have cared less how long this paint stayed stuck to this car. 

About 3 weeks later, it all came off in a big huge sheet of paint.  My friend was pissed, but I told him he pissed off the wrong person looking back on the situation.