Consensus on Lap Joint Weld Prep? Options

[bkrantz]

So based on experience and expert knowledge, what's the best way to prep metal for lap joints, especially with plug welds? No paint or treatment? Ospho? Weld-through primer? And what about seam sealant after welding before paint?

[Costa05]

Definitely no expert here but I lap welded my front half of floor pan to the original rear half and worked real well for me. Weekend warrior in on a fixed budget quality. First grind the lap weld area the best you can to remove any rust areas. I like to use 120 grit roloc sanding discs on an angle grinder and wire grinding wheels. For the more stubborn pitted rust areas apply Ospho (multiple applications) and brush with a small dense wire brush between applications. Rinse with water and dry immediately with a heat gun. Locate and drill your holes for puddle welds over good rust free metal only then apply the weld through primer to both panel surfaces prior to welding. Following welding I apply POR-15 with a brush to drag the sealer into the seams. When cured, use a seam sealer to close off any gaps in the seams using caulking gun or putty knife application. By the way, I like using cleco temporary fasteners on lap welding to hold your panels tight to each other before doing your plug welds. They make it way easier, cleaner results, and stronger puddle welds. (IMG:style_emoticons/default/beerchug.gif)