Paint bubbling horror found under side step.

[Howzat]

Been cleaning the builders sh*te left by the previous owner in the back of my 67 plate van. The side step was horrid so I sourced a replacement and went to fit it this weekend but found this......



The paintwork was bubbling so I scrapped away the loose paint but can't work out what the marks are that seem to have caused the paint to come loose.



Anyone come across this on their van?

 

[Dave Mac]

Anyone of many things cement, brick cleaner, some types of plaster, solvents for cleaning plastics etc. clean it well, prep, prime and paint. As you said it was a builders van his workmanship was probably the same.

 

[Howzat]

The white/brown marks look like they're in the bodywork itself under the factory paintwork.
There were only 3 bubble marks to begin with but when I started scraping those more and more paint started coming way
My initial reaction was to repair it myself as you suggested @Dave Mac. It isn't a big job and doesn't need to be professional because it's under the step anyway but then I started thinking if it was like this from the factory then it might be a warranty claim? The rest of the paintwork in the back is like new. Only this section is bad.

 

[Niknak]

Make sure you rub it down well and do a couple coats of a good zinc primer and then a topcoat

 

[Howzat]

Thanks for the tips @Niknak

Would NO NONSENSE ZINC GALVANISING SPRAY PAINT SILVER 400ML be OK?
Do I need a topcoat as it's gonna be hidden once the side step is put back?

 

[Niknak]

I would still top coat it mate

 

[Howzat]

Roger that. Cheers bud.