I'm somewhat dreading asking this as its a bit complex. I shall try.

I have a motorcycle. Italian. The gas tank is plastic and is painted. Tank is in good shape. I purchased a spare tank as a backup and it needs repainting.

I suspect the seller replaced it as it had started to bubble due to the permeability of the plastic. It is a common problem with these tanks. They also have issues with expansion/contraction. I don't ever leave gas in the tank.

I have a supplied air respirator, paint booth and have done a fair bit of motorcycle painting but this will be my first time trying to repaint a plastic petrol tank. If you're inclined to tell me not to bother, please don't. The tank was discontinued years ago so buying new isn't an option.

Lechler (also Italian) has a good technical note here on repainting plastic motorcycle tanks.

I talked to someone in the UK who repainted the same tank 5 years ago. It turned out great and it's still fine.

Instead of the Lechler LS920 he used Sikkens 2K Plastic Primer followed by Sikkens Autosurfacer primer which I think is a Urethane. No flex additive in the primer. Then basecoat. 2K clear with flex additive.

The problem is that many of these products are not available here in the US.

My local paint shop suggested:
- strip off old paint
- flame seal per Lechler doc
- 1k adhesion promoter
- thin sealing coat of 2k epoxy primer (10% reduced acetone plus a flex additive)
- basecoat
- 2k clear with a flex additive

My only concern is that 2k epoxy doesn't block down well so I'm unsure if I can get a smooth finish since I'll have to remove the old paint using abrasive methods. Advice I got from paint shop was "the less paint the better", the more/thicker the coats, the more chance of cracking due to expansion.

Anyways, long story short. Anyone have any advice?

The 2K epoxy is definitely the right choice, it will block fine if you just let it cure longer,
I let it cure 48 hrs minimum. If it's still gummy, wet sanding will go better than dry.
But either way, after 3 days of being kept warm, it should sand to your liking.

JCCLARK wrote:The 2K epoxy is definitely the right choice, it will block fine if you just let it cure longer,
I let it cure 48 hrs minimum. If it's still gummy, wet sanding will go better than dry.
But either way, after 3 days of being kept warm, it should sand to your liking.

Thanks for the reply. I'll give it a go. Paint store recommended plasticizer (flex additive) in the epoxy and clear.

I was pondering trying this: CP-9600 universal flex additive. It says it works with any paint https://www.cumberlandproductsinc.com/page-7 I'm pretty confident it will work with the clear I have but not 100% sure on the epoxy. I'll call them.

I always end up with diff brands of paint, I'm a hobbyist not a pro, so buying each brands/line of specific flex when I need so little isn't appealing.

I always use epoxy on my bumper repaints, it lessens the rock chips a lot.
I've never used a flex agent in it or the clear.
I don't think it needs it, epoxy stays pretty flexible.

JCCLARK wrote:I always use epoxy on my bumper repaints, it lessens the rock chips a lot.
I've never used a flex agent in it or the clear.
I don't think it needs it, epoxy stays pretty flexible.

This isn't a bumper. It contains fuel. So it has far more "movement" than a bumper.

Not sure on the epoxy but absolutely needed on the clear per the Lechler note, first link in original post

"Application of the lacquer: a two-pack acrylic lacquer or a matt basecoat + acrylic clearcoat can be directly applied. It is absolutely necessary to add 20-30% of 09760 PLASTICIZER to the top coat (acrylic lacquer of clearcoat). Do not use fast or extra fast hardeners which would make the film fragile".

So I'm pretty sure that "universal flex" will work for the clear.

I can't imagine a gas tank flexing more than a bumper.
I can bend the corner of a bumper in half with my hands and
it still doesn't crack.
A gas tank flexing more than that?.

JCCLARK wrote:I can't imagine a gas tank flexing more than a bumper.

Again, it's not flexing in the sense of a bumper. It's a swelling and contracting of the entire tank. A bit like your lungs or a balloon that you let air in and out of.