First think about the objective. The purpose is to remove the seams and enough material around the seams that is not properly filled-in with resin.
Disclaimer: This is my first time, but here is what I did and learnt.
I used the 4" grinder to remove the seams. As I went along, I also removed material near the edges of the seam to ENSURE THE BASE UNDER THAT MATERIAL was solid. The goal was to find air pockets. If there's a pocket, just grind the material away until you have solid surface. Don't be afraid, you can't mess it up, but don't go crazy either. The Epoxy filler will cover all the mistakes nicely.
In the end, I had the seams gone and perhaps 3/4" to 1.5" of material away from each edge also ground off. That gave me the satisfaction of knowing I had solid stuff and no hidden bubbles.
Next. I used masking tape (cheap kind) to tape 2 inches away from the edge and mixed 4 pumps at a time of the West resin/hardener. I used a 1 inch brush to "paint" the epoxy anywhere the grinder left a mark. The objective was to seal the fibers and provide a foundation (not to build up the seam, but to seal it, that's why I say paint it). After an hour or so, I remove the tape and when dry (next day), I used 80 grit paper to start shaping the seam by removing the excess epoxy from the gel coated areas unaffected by the grinding process. If you think about it, the gel coat ungrounded areas are the GUIDES.
Then I tape again, this time a little bit Awa's from the edge of the first tape. Mix the epoxy with resin and 410 to a medium thickness. Not runny, but not too stiff that it is hard to spread. You will know you have it down path if you can spread it thin and yet the mix stays put (say on the fenders). Of course, expect it to sag in vertical areas. Using a plastic spreader (3 inch), I covered the seam from edge of tape to edge of tape (Perpendicular to the seam). STAY THIN, don't try to cover it in one pass. After an hour or so, remove tape, let dry and spend hours sanding away.
After the first coat, you will know exactly what it is you are doing.
Repeat the process 2 or 3 more times. I had to do it 5 in mine. 1 with epoxy alone, and 4 with 410 filler.
Tips:
* Use masking tape to keep the edges of the epoxy from running wild and making sanding difficult.
* On each pass, expand the edge of the tape wider to feather out the effects of the sanding, just like doing drywall, I guess. By going wider, you get a chance to seal over the sanded gel coat.
* Use a flexible board or sanding blocks. Never your hand unless the boards can't be used.
* You know you got it when the edges of the epoxy start to melt down with the rest of the body. That's an indication that you are pretty well faired. Use the finger tips to feel for the edges. Remember that any unevenness of up to a 1/8" can be filled in with the K38 primer. I guess I was anal about it, but figure I'll have more chances to improve the finish when the guide coat sanding takes place.
*In the photos below, you can see where the where the solid WHITE is where grounding took place. The lighter WHITE is feathered epoxy into the gel coat cover. Notice my seams are between 1.5 and 2 inches. The most feathering took place in the front fender wells, which is the most difficult area to sand.
If you look way behind by the garage door, you can see I got so comfortable working with the epoxy and filler I decided to fill in the unevenness around the hood scoop opening and top. PS. A hard rasp SOMETIMES comes handy to shape gobs of dried epoxy before sanding with #80.
[ March 15, 2002: Message edited by: Pepe Borja ]
