In Episode 7 of this project we prepared the chassis for powder-coating. Now we get busy with the plastic powder…
For those of you yet to sample the wonder of powder coating, the process is that a fine plastic dust is sprayed from a gun which has an electrostatic charge. The thing you want to coat has the opposite charge so the fine powder is attracted to it, not only on the side you spray, but also the reverse side and in nooks and crannies that even a Thai football team would struggle to reach.
Once the powder is applied you bake it in a large oven and the powder particles melt into a single sheet of plastic over the entire surface of the part.
Proper painters tend to get a bit sniffy about powder coating, saying it’s a lesser price for a lesser finish. Maybe so, but it has plenty of advantages too:
- It requires much less surface preparation
- It is more durable and scratch-resistant than paint
- Posh finishes like candies and flakes are still being developed
- It requires much less skill to get a good result
As we explained in episode 7, we have a friendly local powder-coater in the form of Gibbo from Nuneaton Alloys and Powder Coating who was prepared to show Sam the ropes so he could do the job himself.
What’s the process?
Stage 1 of any job like this is to clean your junk, even before you remove any old coatings.
Stage 2 – if the parts were previously powder coated or painted – is to dip them in a chemical stripping tank. We covered that in episode 7.
Stage 3 is to blast the parts to remove any corrosion and provide a good keyed surface for the powder to grip to.
Stage 4 is to make any required repairs by welding and grinding of the base metal. If the parts go rusty during repair work they may need to be cleaned and blasted again before coating.
Stage 5 is to apply any powder base primer. In many cases the top powder colour can be applied to bare metal, but where there is corrosion you can apply extra layers of primer powder to level the surface for a smoother finish. This primer would then be baked.
Stage 6 is to apply your main powder colour which is again baked in the oven. Temperature and duration varies according to the size of the part and the powder used.
Stage 7 only applies to parts requiring a high-gloss finish. After the main powder colour it is also possible to add a powder-coat clear lacquer before a final bake of the parts to produce a smooth shiny surface.
Easy does it
The key problem areas of powder-coating scooter parts are simply due to the thickness and durability of the coating. For instance, if you go really heavy on the primer, powder and lacquer then you could add 2mm or more of thickness to a part; which is much thicker than a normal paint finish. If you do that to a Lambretta headset top and bottom then don’t expect them to mate together again properly without getting the Dremel out to grind off some of the coating where the parts overlap.
Other areas of concern are threaded areas and places where there is supposed to be metal-to-metal contact. The rear shock mount on a Lambretta frame is a good example. Not only should you mask the thread where the shock nut goes, but also the shaft that the shock slips onto. If you, or the powder coater, fail to do this then cleaning up to fit a shock again will be a really laborious task.
The key here is to either pick a powder coater that knows and understands scooters so that they can mask the correct areas for you, or for you to mask those areas yourself.
Expecting a powder coater who normally does railings and racking to understand which parts of your precious machine need care is unrealistic. You must either take it to a scooter specialist or tell them precisely what to do.
Skill still required?
Painters would have you believe that there’s no skill in applying powder because it naturally wants to stick to the workpiece thanks to the electrical charge. They may even suggest that those doing the actual coating are there because they are unskilled and spent most of their school years bunking off and playing video games. That would be a slur, obviously.
This plainly isn’t true, at least it wasn’t when you watch a novice coating a wheel and adding a bit too much powder in one area which then sagged into a monstrous drip which then baked hard like a wobbly snot trail. Clearly there is some skill to applying powder successfully, but Sam picked it up quickly.
The other skill is knowing which bits to protect from the powder in the first place. For the SuperLui we put sacrificial old bolts in various threaded holes to protect the threads from coating. If you do this, make sure the bolts are clean of oil or it will boil and spit into your new powder. If the hole goes right through then leave the end of the bolt flush with the back of the bracket. If the bolt ends up powder coated on both sides of a hole then it will be a nightmare to get out. Alternatively, you can leave this sort of thing to your powder-coater. They may well have a selection of special bungs that can be used to plug important holes. Anything that can’t be protected with a bolt or a bung must be laboriously masked with heat-resistant tape.
Finally, we got to see the results of Graham McBear’s suggestion about using JB Weld epoxy as a filler on parts that are going for powder coating. Thankfully the tip worked perfectly with no sign of the resin burning, cracking or shrinking.
That’s a tip worth making space in the old brain for then. Just forget everything you ever remembered about algebra and I reckon that’ll be room enough.
Words and photos: Sticky
Next Time: Technical tricks to traverse tank traumas and a few other rebuild tips learned along the way…
Step inside – we don’t do powder coating but we do sell coats