I'd like to hear everyones techniques/opinions on blocking out the last coat of primer/surfacer. I'm using DuPont URO on the car and blocking with 180 dry so far. I have been doing a panel at a time, allways ends up being over a week till I get back to a panel, trying to allow as much time as possible to cure/shrink. I've done a bit of reading here on blocking primer, and I think I know what I need to do next, but I need some clarification on a few things, so here it goes.

1. When I am satisfied that the panel is straight, I am going to apply another 3 coats of primer (using 180 dry till this point). Now I am a bit unsure about the next part, I've read that final sanding be done with 400/500 depending on topcoat. Do I work up to 400/500 (i.e. guide coat/220, guide coat/320, guide coat/400, etc.) or go right to 400/500 after the final application of primer?

2. I have read that finishing with 400 is fine as long as you are using a solid/non-metallic color (which is what I am using). Is this correct? Any benefit to going finer for non-metallics?

3. Wet or dry? At what point should I be adding water, or can it all be done dry and what are the advantages/disadvantages?

Thanks for your thoughts!

After the body is shaped right with no lows or highs apply 2-3 coats of primer like you already mentioned and guide coat. If the primer goes on smooth go right to 400 wet, if the primer is rough I sometimes start with 320 or 360 wet and reguidecoat, then 400, then 600. Guidecoating between grits allows you to see if the previous grit scratches have been fully removed. I prefer 600 grit for both solids and metalics. The smoother the surface the better the paint lays down and flows. I also stack three grey or white scotchbrite pads and rub the surface some as a last step before cleaning for sealer and or paint. The scotchbrite will remove or mellow any cut marks from the block edge you may have that are not visable in primer, just a small step towards perfecting the surface before paint but it does make a difference. Also check over all of your panel edges carefully and sand them smooth, people often neglect or overlook the edges. All the hard work will pay off. I prefer to wetsand in the final stages, better results IMO, and faster. The water keeps your paper clean letting your block cut nice and flat. Bob

10 4 on the scotchbrite. Does your technique change at all when you are getting down to the finer grits? Do you still use the same blocks that you did with the coarser grits? I have been using 3M self stick roll abrasives this far, but I haven't seen rolls finer than 400. What do you use as far as paper and boards?

I appreciate the help, I'm getting close and I don't want to do anything wrong!

dry board paper is available in 320, 360, and 400. but sanding dry can be tough with these finer grits IMO, I use the 9x11 sheets of wet or dry and tear them in three equal strips lengthwise. Mount them on a 9 inch rubber block. Use lots of water to keep the paper clean and it will cut fast. The hardness of the primer also dictates what grit I start with. If the primer is old, say over a month of dry time then it's usually harder than usual so I start with 320 or 360 rather than 400. The finer grit paper will reveal some smaller low spots that were'nt visable when you blocked with the coarse paper and that is to be expected. Also, when you apply these last coats of primer try to get it on evenly. Heavy spots of primer can actually become light mellow waves that are difficult to cut out with the finer grits, lay the primer on as though you're painting the car, nice and even. Bob

Ok, I think I'm clear on everything. I'm getting close to laying on the last primer coats and I'm making sure I have my game plan straight. One thing for certain, I am sure learning allot about this art. Thanks for all your help!

i am by no means a pro in body work. But i had been taught not to wet sand primers. I was told it may soak into any plastic fillers and make them bubble faster. Anyone with more knowledge than me know anything about that?

I've never seen any problems with wetsanding, only excellent results. Wetsanding is by far better for your health. And it has a cleaning effect on the surface of the car, oils float. People have been wetsanding for years. The amount of saturation in filler is debatable I guess. It's interesting that all the polyester primers and glazecoats I've used recomend wetsanding as a suitable proceedure, leads me to believe that short duration exposure to moisture is OK. I use epoxy primer as a base for my fillers and surfacers, which acts as a moiture barrier if the paint surface is opened exposing filler to moisture. I'll keep wetsanding, never had any problems even with cut throughs into the filler. Hell, before the nice polyester glazecoats came out I used to wetsand my filler prior to primer application and never seen any failures. Some testing would reveal what the absorbtion rate is on plastic fillers, maybe someone here can shed some more light on the subject. TTT