Is it safe to weld with factory paint on inside of panel?

[wrench_nz]

Hi

My countries regulating body for car modification/safety has approved a lap join technique for rear wheel arches and even provided an example:

https://imgur.com/l7Wecra

Remove the inside covering would be a hard job for some places around the arch. Iis it safe to leave it there for alternative spot/tack welding around wheel arch? Is there any post welding paint/metal technique to support a job like this?

This is an example of the rear heat affected area on a test piece:

https://imgur.com/9gr7bwJ

Has anyone has any experience doing this? Any tips?

Its a mid 90's japanese car.

Thank you

 

[pedrobedro]

No problem, I just clean it up or wire brush it, zinc prime it then give it a coat of underseal or whatever you use

 

[wrench_nz]

thanks Pedro

 

[hermetic]

Risk of fire is why you always remove the interior trim, there could be flammable sound deadening panels, wiring harnesses, tank breathers or an accumulation of dust and paper junk in there , never weld anywhere you can't get to the back of in a hurry, I used to have someone inside the car armed with airline and water when I was welding!
Phil

 

[Haz87]

Risk of fire is why you always remove the interior trim, there could be flammable sound deadening panels, wiring harnesses, tank breathers or an accumulation of dust and paper junk in there , never weld anywhere you can't get to the back of in a hurry, I used to have someone inside the car armed with airline and water when I was welding!
Phil

This!
When I was young, naive and dumb(er), and before I decided to buy my own equipment and do it all myself, I as good as stood and watched a welder set fire to my interior. He was patching a external sill with it up on a ramp and the smoke was building inside the car - I'd already commented from a distance about "you sure nothings alight" with response "nah its fine, just a little crud burning up" - I soon clocked just how much had accumulated knowing full well it wasn't just a little harmless smoke, ran over, jumped up to open the door to see that both the carpet and the interior sill cover (plastic) had gone up. The flames were just about to make a start on the front and rear seat too. Cost me a small fortune to replace those parts (ignoring the time to have to do a full carpet swap) and the car stank for absolutely ages! If I hadn't been loitering, I have little doubt the whole car would have ended up going up, or burning enough that it wouldn't have warranted saving.
Always strip anything in close proximity, and protect anything beyond that with a fire blanket or equivelant. Sparks and the odd bit of splatter can launch themselves a hell of a distance. If you have a spare someone to keep an eye, use them, else as much as a pain it is, try and make sure you take breaks between runs to get up and visually check alls ok.