New rear sill/crossmember. POR15?? (1 Viewer)

[hodag]

I have cut out my basically non-existent rear crossmember and sill. I built a new crossmember out of 2"x2" square stock. I cut out holes where the body mounts go, but other than that it is a continuous tube.

I want to treat it before putting it back in permanently. I was planning on using POR15 on the inside. I figured that I would tape off the openings, pour in the POR15, slosh it around then pour out the excess. Then paint the whole thing with weld-through primer.

My problem will be when I go to spot weld the new rear sill to the crossmember. What will the heat of the spot welds do to the POR15 inside the tube? Should I plan on resealing it somehow once all the bodywork is final welded?

I'm just looking to not have to redo all this bodywork again in 15 years.

 

[Mace]

I would just use the weld through primer
Weld thru primer, Copper or Zinc?

 

[kevos37]

If your are looking to join 2 surfaces together with spot welding, by all means apply a weld through primer between the 2 mating surfaces. The weld through primer seals and provides conductivity for the weld. Just apply the primer between the sandwiched/encapsulated areas. The primer does not like to be coated over (paint, undercoating etc) it has marginal adhesion qualities, so limit it to your contact point area. If you undercoat then try to weld (depending on the product) you run the chance of starting a fire . Undercoating after the weld is completed would be the safest route. Another idea... you could use stainless steel for the 2x2 sill.

 

[DSRTRDR]

Hi Eric - long time no see

(we moved away from Omaha)

 

[SteveH]

I'm just looking to not have to redo all this bodywork again in 15 years.

If you make a DD out of it, and live in a crappy climate, it won't even last that long! When you are all done with other metal treatments, apply a grease type (not tar) rustproofing, and this can even be axle grease, to the backside of everything.

 

[1MAC]

POR 15 is not designed to be used on new steel. It will usually flake off if applied without a lot of prep. It sticks very well to lightly rusted steel, but it absolutely requires prep with degreaser and then a metal etch product. The only way it works well on bare steel is if you sandblast first, followed by the two-step prep.
I would use weld-thru primer on the backside of the sill and a wax or grease-based product on everything you can still access. Driving down a dusty gravel road afterward helps to solidify the whole mess!

 

[hodag]

Hi Eric - long time no see

(we moved away from Omaha)

Hey Claudia. Its been a while. I got out of the Cruiser game for a few years while I built a '51 Ford Tudor Custom. Sold the '51 to have funds to work on the FJ40. Now I'm able to do all the stuff that had been neglected (including an LS swap - hopefully).

 

[SteveH]

I would use weld-thru primer on the backside of the sill and a wax or grease-based product on everything you can still access. Driving down a dusty gravel road afterward helps to solidify the whole mess!

Spoken like a true home-brew rustproofer person - good advice!

 

[Splangy]

POR 15 is not designed to be used on new steel. It will usually flake off if applied without a lot of prep. It sticks very well to lightly rusted steel, but it absolutely requires prep with degreaser and then a metal etch product. The only way it works well on bare steel is if you sandblast first, followed by the two-step prep.
I would use weld-thru primer on the backside of the sill and a wax or grease-based product on everything you can still access. Driving down a dusty gravel road afterward helps to solidify the whole mess!

True, except you would wouldn't degrease and etch a freshly
sandblasted surface. Degreasing should be performed before sandblasting.

 

[1MAC]

Even better to do it before and after. Unless your blast media is brand new (unlikely), you're probably putting grease back on the parts when you blast them. I degrease all blasted steel prior to priming or painting - it's specified in the instructions for the epoxy primer I use.