OK, but what I use is NOT "relatively safe" by any means! It contains isocyanates (read CYANIDE)! But it sure is durable for paint. Powdercoatingis the most "durable" finish for a bike frame;i.e. harder than heck to chip!
1) I start by removing the old finish; Paint on steel, I have it sand blasted w/60 mesh. Aluminum or Ti, I use Jasco Paint & Epoxy remover. (also good for removing powdercoating as blasting will likely damage your frame because it's so abrasion resistant) Carbon fibre, hand sand with 60 grit for the brunt of the removal. Then 220. Then 320.
2) Then I spray a couple of coats of PPG DPLF (Ditzler Primer Lead Free) in an appropriate color. On blasted steel, do this AS SOON AS POSSIBLE! The more time between blasting & priming, the more likely rust will happen sooner!
3) Now that the first shot of primer is on, I can take my time and clean up all the ****ers. I use ultrafine spot putty to fill rust pits, brazing holes and the like. It's like Bondo, only a finer consistency. You have to make little batches because it hardens in about 5-10 minutes. (you add a catalyst, just like regular Bondo)
4) Once that's all on there, I use 320 wet/dry and sand all the bondo spots smooth. Then I work around the rest of the frame and make it all nice and smooth. I like to use tools like a rounded point paint mixing stick that has about a 3/8" diameter at the tip to go around lugs and such. I also ahve a set of Tadpole sanding blocks for all the other tricky areas. I usually tear the sheet of sandpaper into about 2"X2" squares for use with the Tadpoles.
5) Now the frame is cleaned with 3M Wax & Grease remover as per instructions on can. I wear latex gloves to keep that stuff off my skin AND the fingerprints off the frame.
6A) READY FOR PAINT. I start with a fresh coat of DPLF primer thinned about 10-20% with 860 or 870. The frame is mounted on a special stand that has a 1" peg on top that I slide the headtube over to hold it, starting with the frame upside down. I begin by spraying around the BB and then the rear drop-outs, the brake bridge and then the seat cluster. Then I go go back to the BB and connect them to the drop-outs, and then the seat stays. Next is the headtube area. Now I spray the downtube, the top tube and the seat tube.
6B) I go to the other side of the frame and repeat the process, starting at the BB.
7A) I put my fingers in the BB shell & the seat tube and carefully flip the frame right side up and put it back on the peg.
7B) I start on the left side of the frame and begin at the seat cluster. I do the brake bridge, drop-outs & top of the BB. Then connect the seat cluster to the drop-outs, and then the chainstays. Next I spray the seat tube, top tube, head tube and then the downtube.
7C) I go to the right side of the frame and start at the seat cluster and repeat 7B to get a nice even coat.
I use an HVLP deatil gun with the fan pattern set on round. It takes about 7-10 minutes to spray ONE coat.
If I don't have any runs*, I wait about an hour before spraying Sikkens color(s) in the same pattern as above. I have turned the frame upside down again.
*IF I have any runs, I let the frame hang out overnight to cure. The next day I sand the runs smooth, using a small block of hardwood and being carefull to ONLY sand the run itself. I try not to sand through the primer down to the frame!
The window for DPLF is about 24 hours so I don't have to sand the whole frame again, just the runs.
8) I spray 2-3 coats of Sikkens with about 15 minutes "flash"time between coats. More time if the coats are thick, which ideally, they shouldn't be.
9) I wait 1-2 hours and then spray 3 coats of PPG 2042 clear in the manner described above. About 20-30 minutes flash time between coats. I try to get the last coat on quickly & evenly so that there are no dry or dusty spots and not so thick as to get runs. Then there won't be any time wasted trying to sand/polish the final finish.
10) Let the frame hang on the painting peg or on a peg elsewhere for about a week. If you can make an imprssion in the paint with your fingernail, let it hang some more. I usually check somewhere on the drop-out where the axle will be. Autobody shops have the luxury of "baking" the finished paint by heating the paint booth to about 140 degrees for about an hour.
Notes;
1) If you get runs in metallic/pearl colors, you will have to sand and respray those spots. Sanding metallic/pearl colors will scratch the flakes and clearing over that will NOT make it go away.
If at all possible, DO NOT SAND ANY METALLIC/PEARL COLORS!
2) If you want to add decals, pin striping etc; spray the color and only spray 1 (ONE) coat of clear. Let the frame sit overnight. Add decals/stripes etc and then go ahead and spray 2-3 more coats of clear over all that. If you are doing other art with say artists acrylics (in tubes) let the frame hang overnight (or 2) THEN SCUFF WITH FINE SCOTCHBRITE PADS. Clean with Wax & Grease remover.
THEN add your art/decals/stripes etc. Gold extra fine point paint pens work great as long as your careful. Slip? CAREFULLY remove the offending glitch with a paper towel dipped in 860/870.
Now you can clear with the final 2-3 coats of clear and the clear will stick properly. If you do the final work within 24 hours, you shouldn't have to scuff the whole frame.
Catalysed paints have a "window" of time where the next coat will stick without having to scuff or sand. Go outside that window and you WILL have to scuff/sand before applying the next coat. Got that?
3) DO NOT spray the final clear coats at the end of the day if it is going to be cold that evening. You run the risk of a NASTY problem called SOLVENT POPPING!
That happens when the paint skins over before the solvents have had a chance to escape. The result is little tiny "champagne" bubbles in the clear. They can NOT be sanded out as they are deep in the clear coats.
YOU WILL HAVE TO START ALL OVER AGAIN!!!
Dirtdrop, hope that answers some of your questions! If NOT, let me know and I'll do my best to help you out! Or ANY ONE for that matter. You can PM me, email me at
mb@mbent.net or call me 831-521-3801 California time.
Cheers & good luck to all,
Dr. Deltron