Step #1 - Plastics Prep

[Cheriff]

This is the year that I am repainting my Kat. This warm spell that is passing through is my reminder that I need to get started. So, that brings me to Step #1. - Prep.

I've read a lot of good threads about painting and sanding but I still have some unrest that has kept me from putting sandpaper to plastic. A PO had previously tried a rattle can job but I have to respectfully say that it appears it was done in a hurry. So it was my thinking that I wanted to get down below this layer of paint before adding my own. In that case, what special instructions do you guys have? Things I still have questions about are:

1. Sandpaper grit progression
2. Since I will likely expose plastic in a few spots, I was going to use an adhesion promoter. Do I get it all sanded nice and smooth then apply this, then prep sand this for the primer that will follow?
3. When do I switch to wet sand?
4. Since I don't have a definite color or brand picked out yet, is it best to hold on the primer so that it can be applied with the same HVLP gun when it warms enough to spray the color coats in the garage?

Some additional background: I plan on using a 10 gallon (5.1 CFM @ 40 & 4.2 CFM @90) compressor, a "cheap" Coleman HVLP gun (may buy one I have heard good reviews about from Harbor Frieght if this gun turns out to be crap), two inline water desiccant "snakes" to filter out water and dirt, a new air hose, and since my compressor is a little undersized I was going to break the work into two or three batches. My paint booth is going to be a false room I set up in my 2-car garage with the walls made from plastic drop cloth.

Any help to get me going would be appreciated.

[Kreylyn]

Start with 200 grit, and sand as far as you feel you need to go down to get a smooth surface. Unless the paint is pealing, seperating, or otherwise did not stick, you won't need to sand it all off normally. You should end up with a surface that is mostly smooth to the touch, and looks like it's almost ready to be painted.

Apply a primer. If your starting with rougher pieces, a good filler primer is a good option here. Once dry, here is where you will wet sand. Useing a spray bottle or bucket, drop of dishwashing soap in the water, wet the paper/piece and start to lightly sand to smooth the entire surface. Tip: if you very lightly dust a different color primer before wetsand, it will very clearly show you any low spots or ripple that need to be wetsanded out.

If you sand through any spots, reapply primer and wet sand again. Final product should be smooth but fully primed surface.

Next round would be a sealer primer, then color, then clear... no sanding between.

That would be the basics..

Krey

[katanawarrior]

Start with 200 grit, and sand as far as you feel you need to go down to get a smooth surface. Unless the paint is pealing, seperating, or otherwise did not stick, you won't need to sand it all off normally. You should end up with a surface that is mostly smooth to the touch, and looks like it's almost ready to be painted.

Apply a primer. If your starting with rougher pieces, a good filler primer is a good option here. Once dry, here is where you will wet sand. Useing a spray bottle or bucket, drop of dishwashing soap in the water, wet the paper/piece and start to lightly sand to smooth the entire surface. Tip: if you very lightly dust a different color primer before wetsand, it will very clearly show you any low spots or ripple that need to be wetsanded out.

If you sand through any spots, reapply primer and wet sand again. Final product should be smooth but fully primed surface.

Next round would be a sealer primer, then color, then clear... no sanding between.

That would be the basics..

Krey

Make sure when you buy sandpaper, you buy the WET/DRY kind. The regular ole' sandpaper likes coming apart once its good and wet

[Cheriff]

So does the Bulldog Adhesion Promoter qualify as my filler and "base" primer?

[Cheriff]

So now I am thinking that I don't need the adhesion promoter unless I sand down to bare plastic. Is this true?

[Kreylyn]

I've never had any spots turn loose with primer at 200 grit, or even 400 grit sanded down to bare plastic. Can't say it won't, just my experiance. You should not need adhesion promoter for paint to stick to the primer.

Krey

[Cheriff]

So paper hit some plastic tonight. Started with 180 (didn't have 200, figured it was close enough). I started small tonight - worked on the third eye and small front nose piece. They feel relatively smooth although they still show some grit induced swirl marks. In some places I can tell I made it to the plastic; I can see hazy black, grey, maroon, grey again, then another black. I have definitely already learned that convex surfaces sand much faster than flat and concave surfaces. Also, when it is time for more critical steps, be very careful sanding off of edges. I'm thinking of using the adhesion promoter just on the spots that are bare. Sand that with 320, then apply the filler primer to the whole part. Sound like a good idea?

While sanding I found that two other fairing pieces have small cracks in them. Grumble... grumble...

[Kreylyn]

Sounds like you got the situation in hand...

Krey

[kevin2502000]

I never used anything but primer when I went to bare plastic. Paint sticks. Sand 320-400 grit to prep for the primer. 600 grit once the primer is dry. I used 220 grit when I used the bodyfiller to take it down fast, then 320. On your cracks, especially if they are stress cracks, read my success with Goop. I used it to reinforce my cracks in the back and then grind out the cracks and apply the filler. Gives it superior strength with a tad of flexibility so it won't crack again. It also absorbs some vibrations because of the consistancey. Be prepared to get pizzed off for not succeeding first time, it takes practice to figre out how the stuff flows.

[Cheriff]

What products are recommended to wash the fairings off prior to applying the base primer? I am assuming there must be something to ensure the surfaces are free from grease and oil. I couldn't find anything at Pep Boys.

[kevin2502000]

Buy a can of denatured alcohol, it evaporates and cleans perfectly. Wear vinyl gloves though to prevent your work from getting oil from skin back on it and to not dry out your hands. Use lots of clean paper towels and throw them away frequently.

[Cheriff]

Thanks.. I think I am going to wash with regular car wash first to get rid of the sanding dust first, then use the alcohol before spraying the primer. Sound good?

[kevin2502000]

yep. I always washed it off twice with the alcohol because I had to deal with fisheyes before and they suck!!! Don't be afraid to put pressure on it when rubbing to get it all.