How to paint your motorcycle parts

Resprayed tank

Resprayed tank

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Have you got an air compressor at home, with a spray booth and a decent paint spray gun? No? Out of luck eh?

Maybe not.

Who says you can’t paint some (or all) of your motorcycle project in your home shop with aerosol paint? Will you get the same result as a professional painter with a spray booth? No. Will it be a show-winning paint scheme? No. Will it be as durable as modern 2-part automotive paints? No. Will you have to spend time and money to strip it off if you change your mind and send the job to a professional? Yes. But do you want to learn some new skills? And have some fun? And get the satisfaction of doing-it-yourself?

Ok, stick with me, and speed up your learning curve.

The haters, trolls and purists will scoff at this article, but who cares what they say?

You can get an acceptable result painting in your home shop if you learn, practice and follow a process. Of course, go talk to your local auto body supplier for detailed product information and recommendations when you are ready to start. With the information in this article you should be able to ask intelligent questions.

Step 1: What does the final outcome look like?

Try thinking about the final finish. What colour scheme does my project have? What sort of lettering? Decals? Patterns? Lines? Flake? Flat colour? Gloss? Matte?

Once you have a final finish in mind, it will help determine the painting process and products needed. Again, ask your local auto body supplier for specific recommendations based on what you want to achieve.

A rough design of your paint scheme will help you plan the painting steps, so don’t be afraid to make a sketch of your tins with your design drawn in. For a flat single colour, you can skip this step.

Step 2: Choose a paint system.

Since we’re assuming you don’t have an air compressor for this process that limits our paint selection a little.

Just quickly, lets cover some terminology you might hear around paint technology.

Single stage paint is one where the colour and the gloss are achieved by a single paint coating. Two-stage paints require one paint layer for the colour, and another for the protective clearcoat (which could be gloss or matte). These two-stage products are commonly called basecoat/clearcoat systems.

1K coatings refers to coatings that do not require a hardener, activator or other product to cure. House paint is a simple example of such a product. 1-Shot pinstriping enamel is another. Most aerosol paint falls into this category. 2K coatings are products mixed with a hardener just prior to spraying to activate a chemical reaction during drying. This provides a durable finished surface much less susceptible to damage from weather, UV rays, fuel or chemicals. Your average body shop will be spraying a 2K finish on modern cars in their spray booth.

As with everything, there are exceptions. Some vendors can supply an aerosol can that delivers a 2K clear coat. They manage this with a separate chamber in the can that contains the hardener. Right before spraying, you activate the hardener supply and it mixes with the clear coat. You then have a limited window to spray the clear coat before the paint in the can “goes off”.

And of course, you could have a 2-stage paint system with a 1K basecoat (colour) and a 2k clearcoat. Online sources like Eastwood are a great place to start to investigate your options.

Here’s a project of my own: I resprayed my ZX9R commuter bike in black and gold, with a 1K basecoat – both the black and gold – and a 2K matte clearcoat over an eBay sticker kit.

Resprayed ZX9R

For the tank I painted for photos as part of this article, I used a high-quality (read: relatively expensive) enamel aerosol paint from the hardware store, for a couple of reasons:

  1. The re-coating time was fast, about 20 minutes. I had lots of paint to lay down, and a deadline for this article.
  2. This tank was full of rust holes, so would never go back on a bike, and would only ever be garage art.
  3. It was far cheaper than a “proper” automotive paint.

If you wanted to tackle a project like this, I would encourage you to do something similar: find a surplus tank or fender and practice some of these techniques before you aim the aerosol can at your project bike. And worst case, if it doesn’t work, or you don’t like it, strip it off and start again.

Is there better paint for the final finish on your bike than hardware-shop enamel? Yes! Your paint product availability will vary depending on where you are in the world, so go ask your local suppliers for advice, or check out the Eastwood site and their resources.

Step 3: Preparation

The preparation is crucial to a quality finish. This is my general process:

  • Remove paint
  • Fill
  • Sand (repeat the fill & sand process again if needed)
  • Prime
  • Spray putty/filler
  • Sand
  • Prime

Remove Paint

You can repaint over an existing coat, whether this is a frame or a tank. If the paint is in good condition, you can simply scuff it up with 400 grit wet-and-dry paper and paint over it. You might be taking a risk with compatibility with the original paint. Test the existing paint. Hold a rag soaked in general purpose thinners on the paint. If the thinners dissolves the existing paint, consider stripping it off.

I much prefer to strip to bare metal regardless. I like to know what I am working with. You can see my favourite methods of removing paint in this article, but paint stripper is available in aerosol cans which might be suitable for a smaller motorcycle project.

paint stripping disc

On our project gas tank, I’d previously sanded the paint off. The downside of sanding is deep scratches in the metal. The strip-and-clean discs are a clear winner here.

You might see advice about preventing or neutralizing rust on your bare metal. I normally skip this as I go straight to the next step within hours of stripping the paint.

If you have purchased a new reproduction tank that’s clean, straight bare metal – you get to skip this step.

Fill

On a new or reproduction tank, you might be able to skip this step. You might also skip this on a frame. Otherwise, line up some automotive body filler. This is normally a two-part product. You need to mix a hardener with the filler to set up the reaction to cure the product.

Before mixing up the filler, put on some disposable gloves to protect your skin. Use Wax & Grease Remover with a clean rag, and wipe over the tank to ensure it is spotless and ready for the next step.

You’ll need a surface to mix the filler. Some sources suggest cardboard will absorb resins from the filler, so I use a $2 plastic chopping board from that big Swedish furniture store. Pick up some plastic body filler spreaders. These are a buck or so. The ones I bought had a slight moulded curve and a bevel on the knife edge. You could use any stiff plastic card if you were really on a budget.

Follow the instructions on the product packaging. Mine said something like “mix 1 part hardener to 50 parts filler by weight”. I have no idea how you’d actually do this. I scoop out some filler with the spreader and squeeze out a thin line of hardener across the filler. Use the plastic spreader to continually fold the mixture into itself until it has a consistent colour and texture.

You need to keep moving now as the filler is starting to cure. Use the plastic spreader to drag filler over the surface. I hold the spreader with thumb on one side and three fingers on the back. I can then curve the spreader to match the surface better. With a few attempts, you’ll determine the best angle and pressure that leaves a smooth coat on the surface. It seems filler manufacturers want you to apply a coat no more than 3mm or 1/8″ thick. If you have a deeper dent to build up, apply 3mm then let it dry before applying further coats to build it up.

Filler applied

You’ll find the filler getting harder to work as the minutes pass. Just mix up small quantities so you don’t waste any having it cure before you can use it. Aim to smooth out the filler as much as possible; leaving mounds and humps in your filler will add a lot of sanding effort in the next step.

Sand

Once the filler has cured (around 30 minutes if all goes well), you can start sanding. Keep the cost down and build up your guns by hand sanding. I aim to remove filler as quickly as possible, without leaving massive scratches that I’ll have to fill again later. My hardware store stocks 80 grit aluminum oxide paper in bulk rolls so I start with this. The 80 grit doesn’t leave significant scratches, and the aluminum oxide paper resists clogging.

While researching for this article, I found this 5lb-box of assorted grit paper which would be a good option if you wanted to order online. I also use a colour sanding block, which is a firm foam pad that you wrap your abrasive paper around. Rather than a hard, straight block – which is fine for straight, flat surfaces – the colour sanding block conforms to a curved surface like a tank or fender.

Filler sanded

With some reasonably coarse paper wrapped around a colour sanding block, start smoothing out the filler. This is dusty work so wear a disposable dust mask. Keep working though your supply of abrasive paper until the filler is only left in the low spots, such as dents.

Run your hand, palm down, over the surface. You’ll feel any low spots. The filler in these areas isn’t high enough to match the existing surface.  Mix up some more filler and repeat the filling and sanding process.

This step will likely take the longest, but is the foundation for your paint finish. In the tank I painted for this article, I spent around four hours filling and sanding. Mostly sanding. Be aware that while it might look great at the filler stage, the first coat of primer will really help highlight any flaws in this step. If you can see the flaw now, you can guarantee it will be visible under paint. Now is the time to patch with filler and smooth it out.

Before your progress to the next step, I would recommend progressively finer sanding with 120-240-400 grit papers. I’ve found I sometimes have trouble covering 80 grit sanding scratches in the priming and painting stages if I don’t smooth the filler coat further.

Prime

A primer is used to provide a key between the surface and paint, or in this case, between the filler and paint. Your paint supplier will recommend the best primer to suit your final paint finish product. The packaging will suggest how thick to lay it on – probably something like “apply three or four light coats” – and how long you need to wait between recoating.

Tank masked pre paint

Before you shoot any primer, you’ll need to use tape to mask off any parts that don’t need paint, like the fuel filler. As shown in the photos, I also masked from behind the tank seam to prevent any paint blowing onto the underside of the tank. I use a reasonable quality painters tape, not cheap domestic masking tape.

At the absolute last second before painting primer, or any coat for that matter, use a tack cloth and wipe the surface you’re about to paint. The tack cloth will pick up any dust or dirt that has settled and minimise how much ends up in your paint finish.

First primer coat

The primer you use might contain some filler product to help smooth the surface. If so, you can sand the primer. You might use a 240 grit at this stage, then a 400 grit before the next step. Taking the high spots off will level out the surface further.  If you sand back to the body filler, prime it again before moving to the next step.

If the primer doesn’t contain any filler (or enough to cover any marks) you might add the next step.

Spray putty

If you find some minor scratches in the primer, a spray putty can help fill these. Again, follow the product instructions. The spray putty I use suggests three to four coats, then sanding. Again, you might end up sanding the majority of the putty off and find it only remaining in the low spots.

Spray putty applied

Check your spray putty coverage and sand any marks out. Spot patch with more body filler if the spray putty didn’t cover up your earlier sins.

Spray putty sanded and additional body filler applied

Give it a final sand and check with your hand again. Hopefully you can’t feel any more marks in the surface.

Final sanding complete

If you’ve sanded back to bare metal, or the product recommends more primer over the putty, spray it on before moving to paint.

Another primer to seal the filler

Step 4: Painting

Now is a good time to explain spraying technique in detail. This applies to primer, spray putty, paint and pretty much any other aerosol product.

The objective is to apply a consistent thickness of product over the surface. On a high end spray rig, you can set the air pressure and fluid flow to achieve a desired spray pattern. With an aerosol, you don’t have this luxury; you just work with whatever spray pattern comes out of the can. What you can control is the angle of the can to the tank, how far away you hold the can, and how fast you move it. The combination of these three factors will determine the paint coverage on the surface.

To achieve the constant surface coverage, the spray needs to be kept perpendicular (right angles), a constant distance from the surface, and moved at a constant speed. If you move the can further away, the paint will disperse more and result in a thinner coat. Closer will give you a thicker coat. Faster movement will give you a thinner coat. Slower movement will give you a thicker coat. As you move from the side of the tank around to the top, you need to move the can to keep the spray at right angles to the surface. Otherwise the paint will be thicker where the can is closer to the surface.

Each aerosol brand and product will deliver a slightly different spray pattern. You should spray a test pattern on some newspaper or cardboard so you can see what you’ll get out of the can. More expensive automotive aerosols might be fitted with a nozzle that delivers a fan, much like a spray gun. Cheaper aerosols will deliver a conical spray pattern, but I find the fan pattern helps to deliver a consistent surface covering.

You have to experiment with your aerosol spray cans to see how far away you and fast you need to move to coat the surface. Spray some test passes on some cardboard and inspect the finish. On a vertical surface, too much paint will run and require more colour sanding to repair, but light coats can be easily built up further. If you’re building up a solid colour, who cares if it takes four coats to get it right?

Check the paint can instructions – there might be specific times for recoating, sanding and final cure. Of course, your local weather conditions (both temperature and humidity) will play a part in how your finish cures. Ask your paint retailer for advice if you are painting at either end of weather extremes.

On our sample tank, I wanted to have the option of “aging” the finish (faux patina) by rubbing through the top coat to reveal a coat underneath, so the first step was to spray two coats of red paint onto the primer.

Preliminary coat of red

Next was three coats of the base cream color:

Cream paint applied

Since my design included a central blue stripe, cream stars down the centre and red accent stripes, I needed to plan the steps to achieve this finish.

First was to print some star-shapes out, and use them as a template underneath some masking film to create five identical stars that I pressed onto the cream surface. Using a good-quality vinyl tape, I laid down the edges of the blue stripe. This tape is designed for painting, and should prevent any bleed, leaving a crisp line on your surface. The rest of the tank I protected with masking paper.

Stars masked out

Now it was time to shoot the blue stripe down the centre. In this photo you can see the star-masks that will reveal the cream when removed:

Blue centre stripe painted

Once the blue paint had dried, I simply masked it off, and revealed the two accent stripes that were hit with more red paint:

Red accept stripes painted

It was pretty nerve-wracking peeling all the masks and vinyl tape off!

The finish isn’t show-class, but I’d be happy to paint something like this on my own project bikes:

Finished tank 1

Finished tank 5

Finished tank 4

Finished tank 3

Finished tank 2

Step 5: Colour sanding & polishing

Once the paint finish is completely cured, you might want to consider colour sanding. There are a couple of reasons for this:

  1. You might have minor blemishes in the finish you want to remove
  2. You might have an “orange peel” finish you want to smooth out, which is what happened with our subject tank.

“Orange peel” is a mottling of the paint surface that literally looks like the peel of an orange under the right light. If you ask the internet you’ll find a hundred explanations, mostly involving application technique, paint viscosity and spray rig preparation. Since we aren’t working with a spray rig, we’ll just have to work with whatever we get out of the can.

I’ll cover this briefly, as most people won’t have the rotary and random-orbital polishing machines that are virtually essential to this step.

Before considering colour sanding, check with your paint supplier to confirm it’s compatible with the paint you are using.

To achieve a glassy-looking, super smooth finish, you need to use finer and finer grades of abrasives to smooth the surface to the point where any scratches and defects are too small for the human eye to distinguish.

The colour sanding process I was taught by an auto manufacturer for repairing defects and orange peel on new cars looked like this:

  1. Wet sand with 1500 grit
  2. Wet sand with 2000 grit
  3. Rotary machine buff with cutting compound
  4. Random-orbital machine buff with polishing compound
  5. Apply protective wax

Wet sand with 1500 grit

Wet sanding literally means the surface and abrasive paper is wet. The paint dust from sanding is carried off by the water, and reduces scratches in the painted surface. To apply water, you can use a spray bottle, continually trickle water over the surface with a garden hose, or hold the part under a trickle of water from a tap over a sink, or have a bucket of water under the part and continually dip the paper in the water.

The colour sanding block is returned to service for this step as you need the paper to conform to the shape of the surface you are colour sanding.

Using the 1500 grit on the colour sanding block will take the “high spots” off the paint and you’ll see all the “shine” removed from the surface.

Wet sand with 2000 grit

Progressing to 2000 grit paper will smooth the 1500-grit sanded surface even further, making the scratches “smaller” or finer.

Rotary machine buff with cutting compound

Once you’ve sanded out the surface with 2000-grit paper, its time to move to liquid cutting compound. A product designed for machine compounding is preferred. Your autobody supply store can recommend a “system” of products that will work well for the following steps. I was taught with 3M products so I am comfortable recommending their rubbing compound.

A rotary machine buff looks like a large angle grinder, but the spindle speed is much slower than an angle grinder, and higher specification machines have variable speed controls. The slower speed reduces the chance of burning the paint from excessive heat. The machine buff might be fitted with a wool or foam buff, and the cutting compound is applied to the painted surface. The rotary action and polish reduces the 2000-grit scratches even further, but the spinning action leaves swirl marks (light circular scratches) in the painted surface.

Random-orbital machine buff with polishing compound

To remove the swirl marks left by the rotary buff, a random-orbital machine with a foam pad and a liquid polishing compound is the next step.

The random-orbital polishing machine rotates AND oscillates the pad at the same time. This “random” motion, combined with a very fine abrasive in the polish works to remove the circular scratches left by the previous step.

Apply protective wax

Finally, you can protect the finely polish surface you have prepared with a wax. This can be applied and buffed off by machine or hand.

Step 6: Enjoy!

If you’ve followed along and painted your own garage art, test part or project bike, congratulations! Like me, you’ll probably have found laying the paint pretty straight forward, but getting the surface smooth and straight was a big task!

My aim with this article is give you confidence to start tackling simple painting projects. Get out there and have a go!

Ready to start painting? Click here to get the painting supplies and consumables shopping list:

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Matt McLeod

About the Author

I teach people how to build custom motorcycles by helping them build skills and confidence with my coaching, articles and training videos. I provide better technical information for custom motorcycle builders. And I shorten the learning curve getting you there.


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