The first thing I ever had experience of painted in Hammerite was my Raleigh Chopper (push bike) - my Dad did it for me as he did up an old bike for my bithday. Sob sob.
Anyhow. Looked great, scratch and chip resistance was pants.
I continued using the product into motorbike and car ownership. I have never, ever, ever been happy with it, unless the item was not used. Once it was exposed to the vigours of everyday life it fell off and the item rusted.
I won't ever use it on anything I want to protect now. Just on something I want to look clean.
For the underside of your car there are lots more modern (better)products for actual protection. If I want it to be protected and also look good, then my preference is stone chip followed by 2 pack paint. If it's for rust protection there's waxoil, but for the cavities the Waxoil doesn't flow, and I prefer Ensis fluid as it's much more searching.
If you don't use your painted component / car very much, then I'm sure the Hammerite will be fine. If you want to use it a bit more, then reconsider.
From my practical personal experience I would say Hammerite is rubbish as a 'paint and forget' product. And now I'm thinking about it, it's only because of their penetrative (effective) marketing techniques that it's usually the only choice on the shelves (or it was when we were growing up).
Rant, rant, rant!
Shaun
