How much prep to paint my tank?

[wirelessguy]

Hi guys,

Being that I'm not an auto mechanic (nor a painter) I was wondering if anyone could give me some quick advice.

I'm including these hi res images of a tank I recently purchase and threw a couple of coats of paint stripper on. The vast majority of paint is off and I've taken a orbital sander with 80 grit paper to a good portion of the tank and the tank bottom (which did have a fair amount of rust on it).

Black spots on the tank? Is that some sort of paint undercoating? it is the metal itself? is it how rust starts?

I've no cue about these things and just wanted to know if I leave that alone or if I have to buff that out well before I can consider painting anything.

Also any suggestion on the tank underside would be good too. I've gotten a lot of the rust off but there are crevices not easily accessible with the sander. I've gone in and done what I can by hand but am not sure now much more to do. Also do I buy some sort of rust remover? Do I think about a rust bonder (like the POR-15 that I'd normally use inside the tank?)

Thanks.

images:

[81GS750]

Dark spots on tank are the beginning of oxidation. Paint stripper, especially the one called Aircraft Stripper has a tendency to turn oxidation black. Once you are down to bare metal on the tank, scuff it up with 180 grit paper, wipe it down with paint thinner (do not touch with bare hands after wiped down. Oils in your skin can get into the metal and cause paint trouble known as fisheye.), Spray the tank with a "self etching primer" It's really transparent, so your not looking to hose the tank down with it. Self etching primer also is called Acid Etching Primer, it will temporarily stop oxidation from forming and provides a suitable substrate for the primer/sealer to adhere to. Wait for the etch primer to dry (15-30min) and spray a coat of primer/sealer on the tank.

This will seal the tank and protect the metal. Let the primer dry, (12 hours is usually good), take a can of black spray paint and lightly coat the tank, this is your "guide coat" block the tank with a block wrapped in 400 grit paper make sure you keep the paper wet with water. What you want to happen is you sand away just enough of the guide coat to leave the primer level. Be sure you use a block and not your hand when sanding, using just your hand will leave grooves in the primer caused by uneven pressure on the sand paper, also known as "finger f***ing the primer" and that's not a good thing. Once the primer is sanded and smooth you can start you painting. Make sure you wipe the sanded primer with some sort of paint degreaser, the oils in your skin will seep into the primer and your paint will "fish eye" in that area, looks like a crater in the paint.

The key thing to remember with any paint job is that the prep work is THE MOST IMPORTANT part of the whole thing! If your prep is bad, your paint job will reflect it.

As far as the underside of the tank goes, you can scrub the loose rust off with a red scotch brite pad and wipe it with some Ospho. That will kill the rust and you can wipe the white residue left by the Ospho off, acid etch, prime, and paint as usual. Inside of the tank, POR it if it's really bad I guess. I've never used the stuff before but I have a feeling I will be soon with the Honda CB750C I just picked up last Friday!

This is just a basic outline of how to do it. I've been painting for over 12 years, but I don't claim to be an expert yet Hope the info helps you.

[nvr2old]

A wire wheel in a drill will take off what little rust you have left. Spray everything with an epoxy primer to seal the bare metal, then do whatever body work is necessary, primer again with a urethane high fill primer, block sand, and paint.

[Nessism]

I'd use a phosphate wash of some sort after sanding/wire wheeling to remove the rust. Epoxy primer after that to seal the metal. Epoxy primers typically have a limited time before they need to be top coated so pay attention to what the material mfg says. Nothing worse than having a paint job fail because you didn't read the instructions.