Spot Weld and Metal Prep Question

[thetoyotaman]

So, I'm learning about welding, body work and painting thanks to Mud and Mud members. I'd like to know the best way to prep a panel before it is spot welded such as where the rear wheel wells meet up with the rear quarter panels and bed. From what I can tell it appears the factory may have used a self etching primer and body sealer and then spot welded it together and that was 31 years ago. With today's products what are the pros doing to protect from rust and give a factory appearance? Thanks for the help.

 

[TCSTARK]

Interested in this as well.

 

[PAToyota]

I've used a weld through primer such as Eastwood's: http://www.eastwood.com/ew-self-etching-weld-thru-primer-16-oz-aero.html

Then seam sealer on either side of the joint and paint.

 

[thetoyotaman]

Is there a technique to welding two panels with the body sealer in between such as turning up the power or anything? I experimented with that and the welds were not penetrating as well.

 

[PAToyota]

I can't imagine having seam sealer between pieces being welded without it making a heck of a mess. The weldable primer is specially formulated for doing such things.

 

[PAToyota]

Another option over spot welding is to use one of the newer panel adhesives like 3M's product: http://3mcollision.com/products/adhesives/adhesives-products/3m-panel-bonding-adhesive-08115.html

It has a lot of benefits over spot welding.

 

[thetoyotaman]

Would you want to glue the wheelwells on?

 

[PAToyota]

Sure - with the proper prep and using one of those panel bonding adhesives properly.

 

[thetoyotaman]

Well, I have heard of that but plan on sticking to the factory style body work where possible. So, would it work to spray a panel with a weldable self etching primer, assemble, then cover with an Epoxy Primer like PPG when done? Will the Epoxy Primer work over say the Rustoleum Self Etching Primer?

 

[PAToyota]

I always try to use compatible systems. Not a big fan of using Rustoleum under "real" autobody paints.

For the panel adhesive, you're going to a continuous bond rather than just spot bonding with the spot welds. If you look at these areas, usually you start to see a dimple at the spot weld as the bond pulls apart due to load or vibration, then the areas between the welds open up and water and muck gets in there, the muck holds more water, and it starts rotting out from the inside. The panel adhesive gives you a continuous bond so there is less chance of it pulling apart and it seals the entire joint so that water and muck cannot get into it.

 

[thetoyotaman]

That's a good point. Sounds like it's better to assemble and then coat with some epoxy primer then.

 

[Splangy]

I use weld thru primers when "spot" welding. I usually have to crank up the welder a little bit more when using weld thru primer. It's conductive, but not conductive enough to get the same quality weld as without it.

 

[thetoyotaman]

I have always heard that primer absorbs moisture. Is that true? That's one of the reasons why I've wondered about the metal prep and spot welding.

 

[PAToyota]

I have always heard that primer absorbs moisture. Is that true? That's one of the reasons why I've wondered about the metal prep and spot welding.

Not for epoxy primers.