Technical Weld Primer

I'm not a body repair person. So I'm going to learn on my F100 build. Painting is no problem as I used to do cycles and helmets.
I have started to replace the firewall, front half of floor and left side cowl panel,(past owner practiced Swiss cheese look). Very little rust repair below front cab mounts.
I noticed corrosion in the original joints and would like to make an attempt at preventing this from reoccurring.
What is a good product for weld primer that wont affect the weld integrity. Our should I just use seam sealer and forget about it.
This pic is the L front cab mount where the firewall meets floor.

R side rust damage. Both sides about the same.

I picked up some spot weld drills from Fastenal, 6.5mm and 8mm. They are about 1/8in larger than the two sizes of spot welds on this cab. Ford put these spot welds in some screwy places. Some are in radius areas.
I'm not sure about removing the left side cowl panel. Where the side meets the upper cowl there is a joint that I cant get too unless I hack up the side panel, then re-welding the joint there would be difficult.

 

3M and SEM both offer good weld-thru primers. The weld will spit n sputter a wee bit but not enough to rag about, and both are acceptable for ICAR body repair on new shi...uh, stuff. About $18 a can and goes a long way.

 

I use the SEM stuff. Replace the rusted sections then clean the areas as good as you can and spray the product into any surface before clamping them together and fill in the plug welds. Nothing will stop rust forever but it seems to work well.

 

Thanks for the replys
I'll try the SEM brand as I like their products.

 

I like UPOL weld thru. Whatever brand you get, after you use it, be sure to turn the can upside down and spray until clear. The weld thru seems to be pretty bad about clogging the tube, tip. Pretty expensive rattle can, ya wanna use it all.

I use an awl and scratch out the paint in the rosette weld area to start my weld, only takes a second and I know I won't have issues striking an arc.

 

Weld thru primer won't hold back that existing rust, it never sleeps.

 

I use an awl and scratch out the paint in the rosette weld area to start my weld, only takes a second and I know I won't have issues striking an arc.
indyjps, that's a good tip.

 

I can't weld rust very well so I'll be removing it.

 

I like SprayMax 3680001 weld through/self eitch primer, i get it from autobodytoolmart.com. When you are done using it flip it over and spray to clean out the tip.

 

make sure you use a respirator, most of the weld primers have zinc in it. Can be some nasty stuff!

 

Good info.
Thanks.

Ima bout 2 weldin sum cherokee rockerz. (not exactly a hotrod) : (

Its gotta inner and an outer panel... and they pinch seam at the bottom...

reckon, I'll weld through primer the whole thing... then scratch the hole to get the arc started... like previously stated...

I have also heard that you should lay the primer on heavy.... as the primer will get hot and almost melt... but then drip down and settle... covering your weld spot.