Continuing on with the floorboards I started grinding down the welds.  I started off using a grinding wheel in the angle grinder but had better luck with a flap disk.

I ground the patches flat on top and tried to angle the sides down to the base floorboard.   It became obvious that my welds were hardly perfect but it is NOT coming off of there and that is all I care about.

From the bottom it is clear I have good weld penetration.  I scraped all the old undercoating and crap off of the weld area then cleaned everything well.

Once cleaned I masked the patch areas with newspaper and old sheets.  Ready to paint!

I think this looks good but that might just be the paint fumes talking.

Underneath I brush primed everything with rusty metal primer.   I thought about using clean metal primer but I had this and there is rust in there too.

I let the primer dry overnight then wet-sanded it.   Once that dried I put seam sealer on the weld.  This is both to actually seal the seam and to help hide my ugly-ass welds.  I did the same thing underneath but did not take any pictures since I got as much seam sealer on me as on the car.  This brush-on seam sealer is super gooey and it was hard to get it worked in to the seams above the frame rails and muffler.  But it does dry fast.

  

I have to put something on top so I just sprayed it flat black.  It looks fine.   The fumes from the black spray paint were even more potent than the primer.  I think I lost some brain cells here.

Here is a little before action here to show what I started with.   Big improvement!  I also crawled underneath and brush painted everything flat black.   That was even messier than the seam sealer so no pictures.