I have an all-white composite model that I want to paint some trim on to give it a bit of life and make it easier to see. I don't really want to paint the whole model.

What is the best way to prep the surface for paint? How do I only scuff the area I want to paint without marking the areas that I don't? Or do I just scuff the whole thing and then polish it pack again?

Thanks

Siclick33,
The best way to do it really is to paint the airplane, however I get your desire to not have to do that. In that case, if the shapes you want to paint are simple, the easiest way is to mask the airplane off like you were going to paint it. Use the 3M vinyl tape (blue) to mask the edges the paint will go up against. Then (preferably) wet sand the gel coat that will be painted with 800 grit paper. Once you are done that, use a grey scotch brite pad right up against the tape edge to ensure the shine is gone all the way up to the edge. Spray your paint, I would use a razor blade to cut the paint line against the tape to reduce the risk or pulling an edge and then remove your mask.

Before you do ANY of that though, make sure you wash the entire airframe with a good unscented detergent with no oils in it for fragrance or moisturizing (tide powder laundry detergent seems to be the best). Then wipe it all down with a good was and grease remover like PPG's DX320 or DX330. Wipe the sanded area's with the DX320 again before painting.
Jeremy

Slick33,
Jeremy is right on.
The only thing I would add is an extra step I do: Once I've got the surface prep completed, I remove the thin line tape and re-tape the design using the edges of the surface prep as a guide.
This will prevent any damaged areas of the original tape from blemishing your paint job.
I also pull the tape fairly soon after the paint is applied - 5-15 minutes depending on temperature ant type of paint. This helps the edge 'lay down' at the tape line.
Painting is 90% surface prep, and 10% paint application.

Good luck, Jim

Jeremy, wouldn't wiping the gelcoat down with acetone or lacquer thinner before sanding work also instead of using Tide?

Thanks

Using solvent based products can be a negative for 2 reasons:

1. It doesn't cut through mold release and remove it, it is more likely that it will soften it and just smear it around, you will think it's gone, but it won't be.

2. Using a harsh solvent like lacquer thinner runs a higher risk of softening the gelcoat and creating problems with your gelcoat base.

As such, washing first with a good oil free detergent like Tide is the safest easiest way to ensure a clean wax free surface.

Thanks.