I am finally ready to start welling parts back on my 68. I am installing a radiator support and fender apron. I know I need to clean the metal on both sides where I am going to do the simulated spot welds. My question is; do I need to use weld through primer on all of these lap weld seams or do I leave the metal bear and primer after the welding? Because these are spot welds I am worried about moister getting in between the two pieces of metal and starting to rust. What have you guys done in the past and how has it turned out?
Thanks.

 

i spray both pieces with weld thru primer. before welding i clean up the area within the hole punched for the plug weld with paint thinner to reduce spatter.

 

Bare metel will give you the best weld. After weld has dried I spray a light coat of primer/ sealent then paint to match.

 

I agree. Clean bare metal will give you a better weld. If the weld is primed and painted, then no moisture will get in. If in doubt, then use some seam seal.

 

Thanks guys. It is going to feel almost therapeutic to finally (after 20 some years of neglect) to finally start replacing metal. No more battery strapped down with an extension cord. No more Re/max floor boards. I can start flipping my cigarette buts out the window like normal people instead of dropping them onto the pavement through the floor board. (I will just need to take up smoking). The only thing I have not figured out is what to do with open containers at check points

 

Trap door. easy installation while the floors are being reworked.

Yeah attaching parts to a car is a good feeling. recently the father in law came over and checked on the projects. He said "Well you sure can take things apart good"... yeah.. now I need to put it together again and make it run..lol.. amazing how one small remark or innocent phrase can change the course of something...


HINT. Before you final weld anything, make sure the fenders and hood line up with where you have it.. put it together, take it apart, back together repeat a few times is par for the course... unless you dont care how it looks in the end...

 

Trying to weld and get the most corrosion protection is a balance. There isn't a 100% solution that I know of because when you weld you melt anything in the direct vicinity of that weld. Unless whatever you spray on becomes activated as a corrosive protectant when the metal becomes red hot then whatever is on that metal is going to burn off.
My experience with weld thru primer is that although it is ok, it will never give you as clean a weld as bare metal.

Here's what I do:
If feasible primer and paint everything first, even the areas that will be welded.
Grind off the paint around the weld area.
Paint those areas with weld thru primer.
Put your parts together.
Wire brush off the weld thru primer right where you will lay down the weld.

With spot weld holes I like to stick ear plugs into the hole so the inside edge does not get painted at all. You can use ear plugs or some other expanding foam.