Sanding after priming

Starting to prime my vertical stabilizer today! Quick question I am using duplicolor self-etching primer, after the last coat and everything has dried, should I run over it quickly with sand paper or just leave it as is? Also, how many coats should be needed to completely cover? Currently on my practice parts I have been doing about 7-8 lighter coats. Should I be doing less? Thanks!

I am no pro but, I assume you are talking about the exterior, I would wait until the end, and use an epoxy like PPG DP40 which is great with aluminum and act as a sealer.

If you are talking about the inside, gents have used Zinc Chromate for years...or not if you are in a dry climate.

Paint is as good as the prep, a ton of people have paint peeling because their primer wasn't good.

I usually clean with alumiprep, prime with epoxy, light coat, sand to 180-220, then use a builder primer 2k, and wetsand to 800 before paint.

( I always measure my weight of material to have the proper thickness)

Priming

Curious why you would want to sand the final coat?
Only reason I know of is it cured and you want to spray a final color over it like an exterior paint. I don't recommend sanding it. You might bust through. If it is for final paint, I recommend an epoxy primer as Erik suggests. I use Kirker EnduroPrime and my process is similar to his mentiined above.

Interior priming for corrosion protection is different. I don't use Duplicolor but my goal is just enough primer to form a layer. Primer weight in the empennage adds up quick. Keep it thin. With P60G2, I shoot one coat of passes over the whole part then another coat of passes 90° offset. Barely a color change. It's a very thin, translucent primer layer.

Priming

Thanks for the input, it seems to have solved my question. The initial reason I was asking about sanding was because the primed practice parts was very rough after curing. I just did a test part with only 3 coats as per instructions on the can (+1 very light) and it seems to have came out as a very thin (almost translucent layer) and it is very smooth with half the primer. Thanks for the help gents!

Finished priming the front spar and doubler last night and it didn't go terribly. For the first side of each part has a relatively even coat and a very smooth finish. After the parts were dried I flipped and continued priming. On the second side after priming (same amount of primer) the finish came off slightly rougher and had a shinny look. Not sure exactly why this happened... It looks like there is a coat of primer (which is my main concern for corrosion protection), but it's doesn't make sense to me. Attached are some pictures:
https://photos.app.goo.gl/jGgQwTvy1nYE3wDH7
https://photos.app.goo.gl/DxErb29yd4Uy1yye8
https://photos.app.goo.gl/ymom8QYuzK4at1yj9
Before each part was primed they were cleared off with an air compressor, and cleaned with lacquer thinner. Thanks!

any non-activated (i.e. NOT a primer + activator) primer requires manual abrasion before top coating, otherwise you will have adhesion problems. Alodine, which is not really a primer (it is a conversion coationg), is an exception to the rule. Be advised that some urethane coatings are not recommended over etch primers. NOt all of acid converts in the etching process and the remaining acid can create curing problems for some two part urethane coatings.

With rattle can stuff, you can often go wet on wet, by getting the top coat on within an hour or less to avoid adhesion issues. The time varies by brand and ambient temps.

wirejock said:

Only reason I know of is it cured and you want to spray a final color over it like an exterior paint. I don't recommend sanding it

Click to expand...

rattle can, etch primer is one part and DOES NOT cure. It only dries via solvent evaporation. There is no chemical bonding or linking, as with two part epoxy primers covered with two part top coats. Without chemical bonding, abrasion is always required for optimum adhesion.

only two part coatings cure after solvent evaporation and sometimes before solvent evaporation if caution is not taken.

Larry