Sanding between paint applications
 

Hey gang, just spent time surfing a number of old threads on DIY paint jobs and thinking I might try my hand at a few pieces. Here is the typical process I read and the questions I have about sanding after application:

• Prep (lots of it)
• Primer coats 2-3
• Sanding primer coats
  • Wet or Dry sand?
  • What grits?
  • Do you sand after final primer coat?
• Color coats 2-3
• Sanding color coats
  • Wet or Dry sand?
  • What grits?
  • Do you sand after final color coat?
• Clear coasts 2-3
  • Do you sand in between clear coats?
  • If so, Wet or Dry Sand?
    
  • Do you sand after final clear coat?

I know not everyone follows this process but for those who do, any insight is appreciated. :)

The more colour coats the better I have found.

If you're going on bare metal, my paint guy says 3 coats etching primer, 2 coats high build primer, then color.

If you put the primers on one after another, wait a few minute between coats per instructions. I'd do a very light sand after that, preferrably 24 hours or more later, then do the color.

You only need to sand if a significant amount of time has passed (see paint instructions). I've done several primer jobs after repair/upcycle jobs, but leave the final coat for the customer, so I don't have much experience after primer.

I would try to get away with 2 light coats of primer. You only need enough to build up a smooth surface. Putting on more is essentially a lazy way to fill in imperfections. Sand with 320. I prefer wet. It's messy but there's better control and it's easier. Frecut and stearated papers work OK on lacquer, but I wouldn't use them with alkyd enamel (most spray paint).

2 coats color. Don't sand between coats unless there's an obvious drip. Sand lightly after. 600 is fine. 400 is fine.

3 coats clear. You want a bit extra so when you rub it out you don't rub through. Let dry a couple weeks if possible. You will probably have overspray to deal with, so for best results rub it out. Wet sand with 1000 followed by 1500. Rub with medium and fine compound. That should give you a nice consistent glossy finish.

Wet sand, always. You'll want to wipe down the paint after sanding.

You want to work up to 400 grit with the primer. At 400 grit, you will be putting on the paint. As the frame gets smoother, step up to 1200, with 600 and 800 along the way. I found that at 1200, I could stop. The gloss took over, and I didn't sand the final time.

It's a bit of an experiment. YMMV.

Plonz, I was wondering, are you planning to use spray equipment or aerosol spray cans?

Rattle can and not doing anything fancy yet. First thing I'm painting is a steel Ritchey stem. It's currently silver. I'll be taking to bare metal and coating with primer, color and clear.

Yes, wet sanding is the way to go. Once I had that figured out, I stopped re-painting bikes. Now I buy bikes that don't need a repaint, or just live with the patina.

Something I do before starting with the primer is to wipe the whole bike/part down after sanding down to the metal with rubbing alcohol to have the cleanest surface possible. Then I was careful not to touch the bare metal with my bare hands so that there was no oily residue that could affect the paint application. And then yes, wet sanding between coats.

It's a judgement call with the primer. If the frame is highly pitted or has some sloppy workmanship the high-build primer will smooth things out. However, too much primer, especially high-build, will dull the crisp detail of fine lug work.



Brent

even with rattle can, get a good respirator. And remember that rattle can from auto and hardware stores will be not as durable as automotive paint

I'm a big fan of wet sanding, too. Easier to do a good job. Generally anything between 300-600 grit seems to work fine. Also multiple coats (no sanding between coats) primer, following the instructions on the can.

Depending on the product, you can layer multiple color coats pretty quickly too (no sanding between coats) but it varies with paint type.

Very fine (1000-1200 grit) wet sanding the color before clear.

Or just skip the whole hassle and have it powder coated. Lots of ways to skin a cat. :P

That's pretty much it. Painting is a hassle if you don't have the time or space. A powdercoat here in New York will run $120. Buying a bike that doesn't need paint is also worth something.

With aerosol paint, I would think the color coats would be much thinner than "automotive" paint, therefore making sanding through more problematic. Personally I wouldn't sand the color coat with anything coarser than 600 or 800 grit.

IMHO, I recommend either Eastwood or Spraymax two-part urethane clear for an excellent gloss. I use 2-3 cans with one tack coat and then one continous wet coat until all dry coat is eliminated and I have no clear leftover. I have yet to put a run in the clear. I always spray in warm to hot weather. The Spraymax flows out slick.

I used to paint detail, custom paint, pinstripe, and full paint autos.
The more sanding (always wet), eventually getting up to the 1000s in grits, the better.
This will give you a smoother and even surface. Use florescent lights to check for straight reflections.
Near the end, many color coats (deeper and richer color), and many clear coats (protection and shine), ample sanding between each coat, then wipe and clean with alcohol (this will clean and slightly smooth out the coat), then next coat.
Finish with some buffing and polishing by hand.

Lots of terrific info and exactly what I was looking for. Thanks all!

Here's a dumb question: Wet sanding. How do you do it? Seriously, I have no idea.

One important thing about wet sanding is rinse and change your paper and water often. A 600 grit piece of paper can become a 1000 grit in a hurry. In my limited experience stick with 3M paper. The cheap stuff just isn't worth it.