Prep for automotive paint? (sand paper grit #)

[fishrdan]

What grit sandpaper should I use for sanding before shooting automotive paint, 320, 400? I'm spraying the transom of my Crestliner 1800 (7'x3') and need to do a ruff and scuff, but don't want to go too heavy and leave a bunch of scratch marks.

The plan is:
1- dewax (acetone, MEK, lacquer thinner, actual de-waxing product?)
2- lightly dry sand with a random orbit sander trying not to cut through the original paint
3- prime bare areas (few) with zinc-chromate primer
4- sand primed areas
5- install 14 SS bolts that hold plywood to transom/knee braces, bolts coated with 5200 and excess cleaned up with paint thinner
6- final wipe down with (acetone?)
7- spray the transom, 2 coats, 5 minutes or so apart as per the paint's directions

I've never sprayed automotive paint (single stage Nason Fulthane catalyzed) and want to check and make sure I'm not messing something up.

Any other suggestions?

 

[thrillhouse700]

Re: Prep for automotive paint? (sand paper grit #)

I'm assuming its aluminum? If so I have no idea but I would love to see finished pics . My buddy and I are prepping a glass boat and we are doing, 80grit for fairing, 120 grit, 220 grit then 320 grit, then primer then 320 again then paint. Right now we are on our last set of patches and half way done with 220. Either way i wish you luck and hope u post pics.

 

[fishrdan]

Re: Prep for automotive paint? (sand paper grit #)

Oh yeah it's an aluminum hull, painted from the factory with PPG (?) paint.

 

[coastalcruiser]

Re: Prep for automotive paint? (sand paper grit #)

Just make sure your primer is really bonded, paint is going come right off no mater how good it is,....just like a chain is only as strong as its weakest link
No expert but think epoxy primer would be bulletproof.
As far as grit, I do cabinets, spray with hvlp clear coat lacquer, and use 220
see if its too fine it doesn't have tooth. if after first coat you see scratches by all means go to finer paper. anyway you can paint over any mistakes so just sand and go for it again.
afterwards give it a good buffing with fine cut polish unless your paint is perfect cause if it is how can you improve on perfection??

 

[Bob_VT]

Re: Prep for automotive paint? (sand paper grit #)

Any bare aluminum needs to be sprayed with a light coat of zinc chromate..... after the zinc chromate you can use automotive primer and single stage (or dual stage) paint.

You can do the wipe down with (or dewax) after the sanding..... sanding is very effective to remove wax

You are on the right track!

 

[Rickairmedic]

Re: Prep for automotive paint? (sand paper grit #)

Bob ya want to dewax first then sand unless of course ya like fish eyes . Almost imposible to get the wax out after sanding. 320-400 last step before shooting paint.


Rick

 

[Rippenlips]

Re: Prep for automotive paint? (sand paper grit #)

Don't know if you have the protective gear? But be carefull, some of the new paints will kill you. You may already know.

Good luck

Jon T

 

[thrillhouse700]

Re: Prep for automotive paint? (sand paper grit #)

Holy crap you are correct, I wear my tyvek suit and my mask and goggles when sanding. The goggles fog up like crazy so i have to remove them or pull them away from my face to unfog them. I get dust in my eyes and it hurts like hell.

 

[fishrdan]

Re: Prep for automotive paint? (sand paper grit #)

I removed the hardware last night and got about 3/4 of the project done today.

- spent 4 hours driving around getting supplies and taking the family to breakfast
- dewaxed the transom 4-5 times
- sanded the transom with 220, then 320
- sanded bottom edge of transom, lots of crevice corrosion
- shot the bare aluminum with zinc-chromate primer
- sanded everything again with 500 grit (didn't have 400)
- installed transom bolts with 5200 and cleaned up excess 4-5 times to make sure there wasn't any 5200 residue on the surface

(sorry no pic's, no batteries for camera)

Going to be up early tomorrow so I can, clean, tack-cloth and spray the bottom 1/2 of transom beige, then Monday spray the top half of the transom blue.

Crossing fingers and hoping I don't have any paint related problems, fisheyes...

(oh yeah, I have a respirator)