I have decided to treat (the bare metal of) the firewall / engine bay with Brunox. This is a kind of OK rust treatment. It doesn't come out in a Dutch anti-rust test as well as Hammerite No 1 rust beater / Hammerite products but it is much better at higher temperatures. Brunox can be baked at 180 degrees C if need be - so I hope it won't come off if the engine bay gets a bit warm (!)
Hammerite has a maximum working temperature of about 80 degrees (I mentioned it earlier - I can't be bothered to check the exact temp spec today sorry - check the tin / check earlier on in the thread if this information is of use to you) so I'm not putting it in the engine bay.
You can see the effect of Brunox working on the metal. Quite groovy...
...after finishing the seam sealer on the underside of the car I started to sand the No1 rust beater primer.
This is a really important step to make. You have to make sure that these rust proofing paints have stuck to the metal surface properly. I can't think of a single rust proofing product that does not have trouble sticking to remnants of old paint (and I've tried a few). By sanding now it is clear to see where the rust proofing paint has stuck and where it hasn't.
After sanding the rust proof paint it (of course) needs another coat.
I like using Eastwood's "pre" to make sure the next coat of paint will stick. As it is so flipping expensive I tend to remove any sanding dust with a damp cloth / towel sprayed with brake cleaner first =>
This gets rid of most of the dust before the expensive stuff =>
To make sure I don't get a nasty mixture of rust proofing paints I masked the firewall
(Top tip - if you ever buy stuff from Amazon their packing paper is ideal for masking!)
And then the next coat of No1 was sprayed on.
As I've gone over the seam sealer too I need to make sure the No1 stuff has adhered nicely to it - there might be trouble ahead...