rust on new arch

so i got my rear arch redone and not had the time to get it painted yet, it has been filled and primered but ive noticed in a few parts that rust is starting to come through again

should i take the grinder to it and get it back to bare metal and put some whatever on it to protect it? welder said it was all undersealed etc but i dont want to touch anything incase it fcks it up for the bodyshop?

Mmm this sort of thing is why I hate bodywork.
Filler & most primers except epoxy primers & red oxide primers are not a proper sealer from the elements & moisture so if out in elements & with UK winter weather this could cause issues.
issue also could be poor prep & treatment to steal before filler & painting.
Ideally that needs stripping right back to bare metal start again.
worth speaking to welder & bodyshop, was welder linked/recommended by bodyshop !?

Only been done like 5 weeks tops ...

Yeah as Mr B said primers are not proper sealers so water can be obsorbedand then into the fillter and if bare metal underneith it can pass through to that and start the whole process off again from the inside out.

Would be worth having a look and getting it sorted now as you havent had it blown over yet. Shouldnt be too much hastle

Depends on where its coming through sye ..... if its just where exposed metal is then just sand it back and treat it .... if its coming through behind filler etc chat with the bodyshop and express your concerns .... primers and such like are porous ...

yeah welder was recommeded by bodyshop, ill visit the bodyshop tonight and see what they say

there is no exposed metal its all been covered over, one part looks like its cracked, dont know if its where the weld is joined i dunno.

was just worried as to if i had it painted would it have started bubbling again a month down the line

Probably best to run it in then mate are you getting somebody else to paint it rather than the bodyshop you used ????

well i was going to get the bodyshop as they were very fair priced with the welding, and they seem a good company, few cars they had in for painting/resto looked very well done (and not cheap cars either, mustang, audi quattro porsche gt3 etc).

I would get them bare metal that to see what been done & be sure treated well prior to filler primer & top coat.
I would of used weldable primer on back of panel overlap & before filler would apply epoxy primer then work on top of that as normal .
Quite a few different ideas on what to do & use & i'm no exert on bodywork as absolutely hate touching it :-P

People moan at Nissan as arches rot after 20years but if bodyshop not top effort it won't last 20months ...
Worth getting in writing what guarantee they have too ...