This custom painting guide will take you through the entire process of custom painting a motorcycle; from prep to finished and clear coated art work.
To start off, I would just like to say that everyone has their own way of doing things from the prep to the final clear, including the tools they use and how they use them.
The following is how I do the prep and paint on a motorcycle from the factory metal on up. It’s not the only way but it’s what works for me I guess.
The first thing that we should take a look at are some of the tools that will be needed.
You’re going to need a grinder for cleaning off rust and smoothing down welds as well as roughing up the metal where you want to fix imperfections with Bondo.
A good dual action (DA) feather edger for the heavy sanding and I like to have a couple of different grits of paper for it ; say #80, and #180 grit. I use the 80 for smoothing out grinder marks and any good two stage primer will fill 180 grit scratches so I use that on the wide open areas .
A drill and a variety of wire wheels , safety goggles , Scotch Brite, sanding blocks, sandpaper ( 80 to 2000 grit ), nitrate or latex gloves, ( nitrate will last longer ) and cotton work gloves , safety glasses, dust mask, putty slick and an air blower should pretty well cover it.
Here below is a picture of the parts that we’ll be working on. Both the oil and gas tank have had extensions welded to them. The gas tank has been Kreemed , (this seals the tank and helps prevent rust ) and pressure tested. Make sure that your customer has had this done before starting the prep. Nothing would be worse than to complete a paint job only to find that the tank has a leak and needs to be re welded. We’ll be doing the frame and swing arm as well.
If you have any sense ,… you’ll have all of these parts sandblasted to remove any rust welding flux and to give the primer a good clean surface to adhere to. I sent the frame out to be blasted ,… but we’ll do the tanks and fenders the hard way. We’ll use the gas and oil tank to demonstrate on ,… the methods are the same for the rest.
I start by washing the part completely down with a silicone and wax remover ( wear the nitrate or latex gloves ).
These parts have been handled a lot by the builder with greasy hands and could have any number of contaminants on them. When you wash with a silicone remover, make sure that you dry as you go or all you are doing is moving the contaminants around.
From this point on I usually put a pair of thin cotton work gloves on when handling the bare metal tanks until I get them into primer. The grease and salt from your finger tips can start problems back up that you have already solved.
Then I take my mini grinder ( put on the safety glasses , you only get one set of eyes ) and go over all the welds to get them as smooth as I can, low spots can be filled later but high spots are much harder to get rid of.
Now I start going over all the same welds with the wire wheel on my drill. This cleans out all the nooks and crannies where that black welding flux can be hiding.
A good selection of wire wheels helps here for getting into tight spots and corners like inside the battery box. Keep in mind that anything that you miss is going to be a weak spot in your job and that anything that you put on top is only as good as what’s underneath it.
Your name and reputation are going on this job , so you want it to look right and last. After I’ve done all I can with the grinder and wire wheel , I use the DA to sand the entire surface to ready it for the body work.
A couple of things about mixing and applying Bondo .
First off, don’t try and apply it all in one coat. It’s much better if you apply thinner coats and work your way up.
The second is to stir your hardener into the plastic slowly and try not to flip it over on itself trapping air bubbles. These will show up as pinholes later when you sand the plastic.
There is a perfect time to sand Bondo: to soon and you gob up and clog your sandpaper , to long and it can be like sanding concrete. If you hit it just right it sands smoothly and quickly ,… so put the beer down and pay attention and always use a sanding block.
Try and have several different types of sanding blocks. For large surfaces it’s nice to have a long block ,… and for those curved surfaces a soft block works well but if you want it perfectly smooth you must use a sanding block.
I use bondo for the main restructuring of the tanks ,… and then change to a polyester putty when I get down to the final finishing touches . It cures faster and sands nicer than the bondo ,… but its for cosmetics only.
Use it to fill minor imperfections like small grinder marks and pinholes etc . In this picture you can see the different colour of the putty from the bondo. The sides of the tank were a little wobbly ,… so I used a skim coat just to smooth it out . Its quicker and cheaper then spraying and blocking coat after coat of primer to get it smooth.
The next step is a coat of self-etching wash primer. This is a two stage primer and must be mixed one to one with wash hardener.
A self-etching primer offers superior corrosion resistance and excellent primer and paint adhesion to steel , galvanized steel aluminum and stainless steel. With this primer there is no need to use metal prep or conditioners which if used incorrectly can cause more problems then they solve.
Once mixed the pot life is about 8 hours so just mix what you are going to use in that time period. Now apply a single wet coat. This primer is transparent and only meant to be used for its adhesion properties so don’t over do it. You can see in the picture that the body work is still visible underneath it.
Ok..Three good coats of two stage high build primer surfacer ,… and wait the proper cure time. This can be decreased dramatically with the introduction of heat. What takes 3 hours at 70F only takes 30 minutes at 140F. If you are going to be doing a lot of this type of paint work I’d look into buying a couple of infra red heaters. They work great for curing your clear as well . I like to hang the parts up when I prime and paint so that I can get around the part 180 degrees and get 100 % coverage.
Now that we have a nice thick coat of primer on the parts, it’s time to sand most of it back off. This is where those sanding blocks come into play again. To make it easier to see where your high and low spots are give the part a light coat of a contrasting colour. This can be done with paint or another colour of primer. I usually use a bit of left over base coat from another job or a light shot with a spray bomb.
Now I’ll start block sanding with 180 grit ,… this is coarse enough to cut the primer down fairly quickly but the sand scratches will fill nicely with my next coat of primer. As you sand your guide coat will slowly disappear. As it does you will be able to clearly see where the low spots and heavy scratches are.
Keep sanding until all of your guide coat has disappeared or until you hit your high spots . These will be either bare metal or Bondo . If you have spots showing, either high or low, it’s time to repeat the process. Depending on how rough the parts and your body work where you may have to do this several times. The important thing is to get it right now. The greatest custom paint job in the world will only look as good and last as long as what’s underneath it.
As you’re sanding you are bound to go through to bare metal in the odd place, usually on high spots and sharp edges. I don’t know about other companies but Sikkens makes an Etch primer in a felt pen format . It’s very , very , handy to have on hand. Just give it a quick shake up, pop off the top and dab it on just like a big ol’ Bingo marker pen before re priming with the primer surfacer.
We’ve given the parts their final prime and sanded them smooth I prefer #400 grit for this but 500 or 600 will do just as well . So we’re ready to do some painting well almost.
I always like to spray a test card and get it OK’d by the customer if possible just so that there can be no back tracking on their part later when they see the painted parts and decide that it’s not quite the same as they thought it would be.
This is especially important if your doing a custom color like this one. It’s a tri-coat . The first coat will be a bright red, the second will be a gold pearl, then the clear coat.
When viewed in the sun it looks red one way, gold the other and orange in-between. The problem being that each coat of gold pearl that is applied changes the colour dramatically .
First we spray the whole card bright red now tape off a couple of inches and spray the rest of the card with a coat of pearl. When this flashes off tape off a couple more inches and spray the rest of the card with another coat of pearl.
You can repeat this as many times as you like and then remove the tape and clear the whole card. Now you will know exactly how many coats of pearl it will take to achieve the colour that you’re after. The customer in this case liked two coats.
Now we hang every thing in the booth, blow any dust off the parts with an air-gun and take a tack rag and go over them to remove any remaining dust and spray the base pearl and clear coats. We’re not to worried about achieving the perfect finish with this clear coat because it’s going to get sanded anyway.
Any surface that I’m going to airbrush on will be sanded with #1000 wet & dry or #800 dry paper. Wet & dry paper is always a little coarser then the dry paper so these two grits are about the same.
By clearing the surfaces before airbrushing if I screw up the design ( of course this never happens ) the worst case scenario is washing or sanding it back down to the clear coat which is no big deal. Respraying the whole part is another matter.
Time to add the graphics. The paint on the bike was very bright so the customer wanted the graphic to be subtle. So we went with just shades of black . I masked out the graphic, sprayed and added some drop shadows.
There was no need to repaint the back of the oil tank so I just taped it up and saved the clear. Anytime that you have a nice sharp edge, you can get an invisible blend by bringing a piece of tape out over the edge by about 1/4″.
As soon as you have sprayed your clear, pull this tape off and you won’t be able to see any line there at all.
After giving all the parts two good coats of final clear, I wet sand the areas where the graphics are with #2000 wet & dry on a sanding block, buff with Mequires Diamond Cut Compound and then 3M’s Finishing Glaze on a foam pad.
Now call the customer and get rid of it quick before something gets dropped on it or the dog knocks it onto the floor. Here’s how the bike looked when it was assembled.