Painting with Urethane - final sanding with 320 grit OK?

[RansomEli]

Just received my Eastwood catalog. Talks about painting. The guideline says you can sand the primer with 320 grit sandpaper before applying a urethane color coat.

The guideline also says you can optionally wet sand with 400-600 grit.

I've always sanded the primer with 400 or 500 grit before applying the final coat. Seems to me 320 would leave sand scratches. Does anyone have experience final sanding using 320 grit?

With the cost of paint nowadays, I'd hate to make an avoidable mistake.

[MochetVelo]

I know a lot of guys use a sealer coat between the primer and finish coat as well.

Phil

[Rusty_OToole]

Some paints will flow out and fill 320 sanding scratches. It can't do any harm to have it 400 or 500 smooth. Your choice.

[Guest martylum]

Ransom--my DuPont procedural manuals advise a final sand with 600 wet or dry before thinking about spraying color coats. I sand the sandable primer coat with 600 grit 3M flexible sanding pads the day of painting then spray a urethane sealer coat after solvent washing the sanded primer. The sealer helps to cover any missed sanding scsratches and makes a beter base for color or basecoat.

320 much too coarse IMO.

Marty Lum

[pacrat]

try to use a color correct sealer, like from light grey to dark grey, 1to 7 shades ,1-2 whites and yellow,4-5-6,reds greens,blues depending on how dark you want them,7 black, dark blues and greens,sealer is cheaper than color,i like 800 wet paper

[nickelroadster]

Most paints are a little different. Follow the directions of the specific paint tha tyou ar eusing.

[whtbaron]

X2 on the checking with your paint manufacturer. That may have been a recommendation for dry sanding with a DA sander where you can get away with slightly coarser grits than wet sanding by hand, but even then I personally wouldn't go coarser than 360. We used to get away with 320 on synthetic enamel jobs, but we also used to call it "stucco" when we shot it thick on rough cars. For most paints I would follow the 360 dry with 400 wet, and then a coat of sealer.

[johnworden1]

Ransom--my DuPont procedural manuals advise a final sand with 600 wet or dry before thinking about spraying color coats. I sand the sandable primer coat with 600 grit 3M flexible sanding pads the day of painting then spray a urethane sealer coat after solvent washing the sanded primer. The sealer helps to cover any missed sanding scsratches and makes a beter base for color or basecoat.

320 much too coarse IMO.

Marty Lum

X2 Good advice.

[Restorer32]

We sand to 600 then seal before spraying color.

[Ernie E]

Hi Ransom,

I would finish with 400-500 grit hand wet block sanded. If this were a BC - CC application I would finish with 500-600 grit wet blocked. DA sanding with 320 grit open coat dry with give you approx. the same surface smoothness as 400 grit hand blocked (but would not DA sand primer on a show finish particularly with a dark color). 320 grit hand blocked wet or dry is coarser then I would finish with but if color sanding non-metallic single stage urethane you could get away with it. Have been painting since the early '70s on the side and full time when needed. Painted many black lacquer jobs in the day and now am teaching hobbyists how-to-paint classes in urethanes.