Technical body repair question??

I repaired the rusted rear quarter panels on my '67 Fury III hardtop with lower patch panels. The left side is pictured but the passenger side was pretty much the same deal. My question is regarding the block sanding procedure. I have the new panels painted with a spray can paint but before I have the entire car painted I want to get the surfaces smoother than they now are.
I have seen on tv where body shops coat the entire area with a thin application of filler then use sanding blocks to show the high and low spots. What is the best type of sandpaper to use to achieve this and is there a filler that is easier to work with than the regular Bondo type? Thank you for any tips and advice.
John

 

Not sure why you painted before it was ready, but if it were mine: sand off the rattle can paint. lay down a good coat of primer. sand with 180grit on a long block. recoat with a different color primer, or mist on a coat of black lacquer from a rattle can. sand with the long board again. low spots will show up where paint isn't sanded off. recoat with body filler if needed, or use something like spot glaze. it goes over unsanded primer. spread a thin coat on everything, & sand again. repeat until you are satisfied.

 

What kind of weld is that?? Mig, tig or oxy acetylene?? Did it warp on you and you have a wavy surface?? You probably need to do some more hammer and dolly work if that is the case.

 

You need a long board, speed board or board file (I have heard all 3 names). Lightly grind the whole area, coat with bondo to a level thickness and sand smooth. Start with 40 grit . Do not over sand. You are looking for a level at this point not smoothness. Fill any low spots and go again. We used to have to start with a Stanley Surform cheese grater to take off the tacky surface but the newer bondo does not have this problem. File or sand as soon as the bondo is hard, about 20 minutes. It will sand easier than if it is fully hard.

Once you have a straight level surface board file again with 80 . Then go at it with an orbital sander and 120 till it is ready for primer. Go lightly with the orbital, gently smooth off the sanding scratches.

When the primer is good and dry hand sand with 100 or 120 and primer again. At this point it should be smooth enough to hand sand down to 400, 600 or whatever you need to paint over.

 

Thanks for the responses. I used a Craftsman Mig welder and did consecutive randomly placed tack welds until the entire panel was fastened to avoid warping. The repair panel pictured was not welded at that point. I use the car daily now and will not be painting it until next year so that is why the panels were painted. The panels were purchased on ebay and required a great amount of trial and error fitting and I am not skilled at body repair but I feel that they now look much better than the rusted out originals.