Well, sort of, but if I said yes I don't think we'd be talking about the same thing. Let me run through the early process real quick and get you to the point of indicator coat and maybe it will make more sense. Oh, and it doesn't matter that its a car rather than a bike, other than you've got acres to sand whereas I can knock off a set of tins in a couple of hours.
OK, first you've got clean metal with a well abraded surface. So if you've welded anything new in there or had any pounding to do with hammers its already done and ground down clean. On top of that you've got a couple of coats of epoxy that seal the metal off acting a water-impermeable barrier. On top of that you laid on any body filler you used and got it all sanded flat using blocks all the way. So at this point you know you have a dead flat surface, but it may not be smooth because of transitions between different materials and of course you've been working with relatively coarse abrasives. You then retouched the epoxy so there is full coverage and then you shot your high build primer, the stuff that requires sanding. Now you're at the point where what you are filling in are minute low areas and sanding scratches from earlier work. You've laid on about 3 coats of your high-build (2-K as its often called) with plenty of dry time between coats so there is a thick buildup of sandable paint to work with.
Here is where the indicator coat comes in. Let's say your high-build primer is light gray in color. Get yourself a spray can of the very cheapest black primer you can find - I mean the real garbage stuff - and stand back about 2 feet and mist a fine coat of that stuff all over your nice new High-build. Don't worry if there are blotches and do not try to actually cover your primer, just make sure its everywhere, just like the nastiest overspray you can immagine. Let it dry over night.
Come back the next day and using about 600p sand paper just sand every bit of that indicator coat off. Sand in long pushes, in one direction, and for goodness sakes pay attention to this one rule - quit sanding when its gone, but get every bit of it off. Got that - quit when you are done, not later. How many ways can I say this, just sand the misted coat off, but no more. What happens as you sand it off is you are sanding off the high spots in the paint first and as the surface gets flatter and smoother less and less of it persists - the moment it is all gone, that last swipe with the sandpaper, that is when you have perfection - and sanding you do after that point makes it worse.
All sanding must - must - must - be done with a block. A long block, a short block, a hard block, a soft block, everything you can find to use as a block, but never sand anything without a block.
And when that indicator coat is gone you are ready to seal the surface with a reduced coat (or two) of epoxy and then go straight to your finish paint job.
You get that indicator coat right and 'black' will pose no challenge for you every after. Oh, and I should tell you, its actually very easy sanding. You aren't taking off much material at all but you have to pay close attention all the time while you're doing it. Just quit when you're done, not later; that's all there really is to it.
atriot:.
