If rust has got into your welds, phosphoric acid is good stuff to get in there after it.It will also clean up all the crud around a fresh weld leaving it sparkly clean - useful stuff to have in your cupboard IMO. I have googleread thatyou don't need to worry about neutralising it, just let it dry. It's readily available on ebay as it's intended for skunk farmers.
my acid dried to a powdery finish, just a quick wipe and then bonda on it... at least it goes black so you can see any other rust....
Welds were all seam sealed it's just where panels have had the transport primer removed that the rust is.
Gotcha. The acid will transform that to bare shiney steel in a few minutes even if it looks pretty bad. I have a pic somewhere if I can find it...
Just buy of eBay 5 liters of QD zinc rich primer we use all day long and it will seal all metals plus 2 years later no rust for £25 quid plus it's an aka lid paint so won't react with other paint
I've used this on some of the bits I've been prepping for the underside of the bus. Seems pretty good.
Ive been looking into Bonda Primer, Im using it on an off topic car, and wondered if it was ok for bare metal or only rust, Seems to be fine on both, but, in its tech sheet online, it can be applied down to O degrees C. https://www.rustins.ltd/images/files/2409-PDS-Bonda Rust Primer and Zinc Oct 2018 PDS.pdf
MetalReady is good stuff for an initial blast on bare metal, although pricey. Phosphoric acid and zinc.
No one seems to be mentioning the real issue here, you're painting at knocking on 100% humidity! You can use the best paint in the world and you'll still get crappy results or film failure/rusting if you do this. Never paint unless at least 4 degrees above the dew point, which at this time of year you won't be able to achieve unless you have a very well insulated and/or heated garage. Dew point calculator. https://www.calculator.net/dew-point-calculator.html
