What should I paint inside of sills with before welding up?

[schnappi]

I'm replacing an outer sill on a 1990 Astra Mk2 and am at the stage where I'm ready to weld it on. All the rot has been cut out and everything has been covered with U-POL weld through primer.

I've read today that this weld through primer is not water proof which sucks as now I'm held up on the job.

What should I paint the inner sill and the inside of the new outer sill with before I weld it up?

Having spent 3 whole days on this sill replacement I obviously don't want to be doing it again a few years from now! lol! Thanks in advance.

 

[Chickenjohn]

Inject the sill with cavity wax AFTER welding.

 

[schnappi]

Thanks, I've started welding it on now so will follow your advice when I'm done. Cheers.

 

[Chickenjohn]

Another thing you can do is have TWO schutz guns. Keep one for underbody and cavity wax and the other for applying stonechip primer and using the clean lance you can paint the inside of cavities. I use chassis black paint for this.

Then when this is dry, the cavity wax goes in.

Double protection!