Painting underside

[malcolm]

I have a few areas under the car which have some surface rust; just on chassis members, not panels. Appearance isn't important as such, as it's right underneath, and it's really difficult to get at, so I was thinking of using Hammerite straight to rust. However, I have found out it would fail if exposed to oil or petrol long term so is not suitable.
I am therefore thinking of using hammerite rust beater No1 as a primer/undercoat, and a normal paint on top - but Hammerite can't tell me if the topcoat would react badly with the undercoat!
It's really difficult to get to the areas I'm looking at, at the rear of the car, so can't get the metal down to "bright and shiny", so what could I use as a primer over a slightly rusty member, and then what topcoat? Ideas?
I know I should probably strip entire car down, sandblast, etc etc, but I'm looking for a simpler way of providing protection against further rusting.

[norman m. macleod]

Hi Malcolm,
Treat the area(s) with POR "Metal Ready" and follow up with POR 15 Paint. POR 15 goes on direct to metal......no undercoat needed. It is a bit on the expensive side (US product), but bullet-proof thereafter.....
I did the entire underside of my 2 + 2 with the stuff (black)...
Regards,
Norman.

[malcolm]

Thanks for that Norman - but with this "metal ready", do I need to get back to clean metal, or can it go on slightly rusty surfaces?

[norman m. macleod]

No need to get back to "clean and shiny" metal, but if possible/accessible wire brush off any loose rust on the surface prior to using the "Metal Ready" pre-paint treatment. When thoroughly dry (see product instructions....) then paint with POR15, brush on OK. I have tried a number of products over the years, but none equal this stuff.............
Best regards,
Norman.

[malcolm]

That's great, thanks again. I'll go for that!

[vrracing]

Malcolm,

POR stands for Paint Over Rust.

One thing to note is that whatever POR touches it stains - almost forever - so be sure to wear throwaway clothes along with a bunny suit with long sleeve rubber gloves and something to cover your face.

Unless you like the splotchy tattoo look!

[malcolm]

Thanks for that - the missus would give me a bad time if I did my normal man thing of diving into jobs in the wrong clothes!

[SteveG]

Malcolm,

POR 15 is an excellent product and I have used it extensively on the underside of my car. The only problem with it is that it will break down with exposure to UV, if you want a black appearance then go over the POR with POR's other product, Chassis Black. This gives a satin almost powder coated look that is really tough and will withstand most harsh environments. Alternatively, should you prefer to finish in body colour the POR must be over-painted with Tie Coat Primer first or you will end up with a paint reaction.

[malcolm]

Thanks Steve, good advice. Where I'm using it, it should hardly see daylight, let alone UV, (unless I roll it!) so hopefully it will be alright.

[trondvo]

Double that, I always use POR15 on the floor, inner or outer.

Inside, the whole floor and sills covered in a rich layer.

Underbody, wherever the original coating is loose just brush/scrape away, wipe off with thinner and apply POR15. You can always spray a rubberized undercoating on top of it.

I always use latex gloves when working with POR15, when job is done just take off the glove, no hole?

Wrap the latex glove around the brush, push the brush into one of the fingers of the glove and make a knot with two other fingers. The brush stay soft for months!