marmalade1

Hello,
I'm in the process of building my first scale plane (http://www.rcuniverse.com/forum/kit-...ld-thread.html) and I'm not happy with the Monocote spray paint finish on the wheel pants. I used an electric sander with coarse sandpaper (50?) followed by a fine 400 grit. I used soap to rinse off debris and oils. Dried. Hung. Sprayed.

I didn't get a rough look on the cowl.

Do I need to re-sand? Shoud I have gone from 50 -> 100 -> 200--> 300 --> 400 grit?

Your experienced opinions are welcome.

PD.

52larry52

My Feedback: (1)

From what I can see in your photo the finish is full of sanding scratches showing in the color topcoat. Most of those deep scratches came from your first sanding with 50 grit and they stayed there even after you sanded with finer paper. Here is what you should have done (starting with a new not damaged part); yes clean the part to get any oil/dirt off, scuff sand it with 100 or finer grit (not 50), clean again (sanding dust), PRIME with a sandable primer and let it completely dry and harden. Sand the primer to scuff surface and remove and minor surface flaws with 400 or finer grit, repeat primer and sanding if needed to remove flaws, clean sanding dust and apply color top coat. The first color topcoat should be just a light "tack coat" to get color on the part and and create a sticky coat for the second and perhaps third and final coat to adhere to. The tack coat should be allowed to only partially dry so the second coat can be laid on wetter and stick to the first coat without running. If a third coat is needed for final gloss allow the second to also partially dry before laying on the final wet gloss coat. Walk away and let it dry. NOW, to fix the part or parts you have color coated with the bad scratches showing you will need to sand the dried color coat with 100 or finer sandpaper, prime and sand, repeat prime and sand until you have filled and smoothed all the minor surfaces flaws (scratches), then apply your first color tack coat over a fully primed and sanded surface (no sanded through spots in the final primer coat), followed by a second and maybe third gloss color coat as described above. Your mistake was starting with too course a first sanding, and not getting the surface flaws filled with a primer before applying color coats. The primer not only fills small surface imperfections, it adheres to the substrate (the part, be it fiberglass or plastic) better than just a color coat with no primer. The final color coats then adheres well to the primer. When you sand the old color coat to repair the damaged parts get as much of the color that you have on there now off before you start the process with the primer coat. You won't get it all off but sand off what you can without further damage to the part. It takes a little time and multiple steps to do it right. Practice helps too!

DavidAgar

My Feedback: (108)

When I do ABS sanding, I never use anything less that 220 grit paper. I always use a primer and typically apply 3 coats. I let the primer dry for a couple of days and then paint. For the seams, I use epoxy finishing resin and micro balloons. I make this mix real thick and when it dry's, it will sand real well with 220. Good Luck, Dave

marmalade1

Thanks for your thoughts. I suspected the remaining scratches were from the first (50). I just didn't know how to proceed.

I appreciate the detailed responses.

PD.

Gray Beard

My Feedback: (-1)

ABS is really soft and requires fine sand paper and do it by hand. Automotive primer and block sanding should save that ABS plastic. It's thin to begin with and the 50 grit could have scratched it half way through the plastic.

flygilmore

What type of primer should be used if you're planning on using TopFlight Lusterkote fuel proof paints?

I have a Tamiya primer (that's really nice) that I use on before spraying Model Masters etc. paints.....could it be used?

Pylonracr

On the few occasions that I have used Lusterkote, I just used their primer. Not knowing exactly what formulation the paint is, I figured their primer would be compatible.

jbarnes

You will get much smoother finish if the paint is warm. Warm some hot water in a pan, sit the can of paint in it for 30 minutes before you spray.

marmalade1

Good tips. Warm paint huh? I didn't prime, but I expected to do a few coats. It seems any visible blemish will show through, and then show through the next layer; so ensure the surface is essentially perfect before spraying.

Next time, it'll look perfect. This time, it's looking decent, but not ideal.

PD.

mgnostic

The people discussing the use of fine sandpaper are on target. One thing I didn't see was the mention of wet sanding. While wet sanding should be done very cautiously when dealing with wood parts, you can dunk an ABS part entirely under water. Wet-or-dry automotive sandpaper is the way to go. Let the paper soak for a bit before you start. 52Larry52 was on target with letting the primers/fillers completely dry or cure and using a tack coat followed further color coats. If your undercoat isn't smooth your top coat won't be either. Compatible primers are important. I have had Lustercoat cause rattlecan primers to lift and curdle, especially if they weren't fully dry. Depending on your patience/obsessiveness level you can go through 3000 grit paper and various compounds to get a finish you can shave with but realistically sanding to a 600 or 800 grit finish will produce a smooth foundation for your color coats.