I've done a few different key-word searches to learn the process of getting from A - Z with respect to preparing the body for primer and paint.
Nothing specific returns when searching for, "Fiberglass prep", "Body Work", "Sanding Fiberglass". So this thread is dedicated to all of the new
builders (like myself) who have little - to no experience with body work.
This post will be edited periodically to update the information. These recommendations come from members of this board. They all have their
strengths, and nobody's method should be taken as 'the golden rule'.
Safety
The pores in your skin open when you have a warm shower allowing the glass particles you just spend the day creating with your sandpaper to enter creating a seemingly incessant itchiness. Take a cold shower, the pores won't open and the fiberglass dust will wash away more readily. Proper breathing protection is important, you can't shower to wash the particles out of your lungs and I can't imagine how itchy it would feel inside your lungs.
And always practice safety when working this. You don't just cough this stuff up. Use the filter bags on your shopvac and suck up the fg dust/particles as you cut/grind/sand them if you can. Fans also help to push the dust out of your work space as you go. If you're working in an attached garage (as I am) take it all into the drive way. Your family will appreciate it.
Tips
When drilling fiberglass, start with a bit that is a few sizes smaller than the desired diameter. The 'glass tends to fray and split, so
working your way up from a smaller hole tends to leave a cleaner edge.
Use gloves at all times, or you'll be scratching and washing your hands for hours afterward. Also be sure to wear some sort of
filter over your nose and mouth. There's no need to ingest that crap.
Work in a circular motion and use little pressure when filing, or sanding. The 'glass eats away quickly and you'll end up with a
bite/valley in the immediate section almost instantly.
Measure twice, cut once. Rework and filling is a pain. I've already nicked through the front side of the light bucket (mine are
hollow which makes it easy for the drill bit to skip through).
Use similar product brand materials, do mix manufacturers if possible
Work on area of the car, don’t jump around.
Get the alignment done before trying to align the body work
Pin the rear of the car first and work toward the front
Do a dry run of everything you need to do before you do it for real with mixed goo. It will pay dividends down the road. You can always grind something off and then remake it with fiberglass
Most obvious tip (but a darn good one), was to use a stiff rubber block for sanding all your seams, soft ones sand on either side of what you are trying to sand.
Once you make the cut or drill that hole, you can not un-cut or un-drill that hole. When the body is laid up as one piece, and you remove part of that piece, there is no way to replace it. Yes, you can take fiberglass and resin and make patches and repairs, but:
1. They will NEVER be as strong as the original part because you are essentially just gluing the patch onto the existing surface. Laying new fiberglass over cured fiberglass does not make it one piece of fiberglass. It will forever be 2 pieces.....glued together by whatever bond strength the resin has.
2. You will never get back to the dimensions of the original part. I've had lots of doors come in on customers cars that the owner has already cut holes in and tried to install the doors. Once you cut the opening out for the latch hole, you can not make it smaller again, or move it over a little, etc. That material is gone. If you find that you cut the hole in the wrong place, and you need to adjust it to the point where the bolts that hold the latch to the fg door are....well, now hanging out in space where there used to be fiberglass.......well, it's not going to be pretty.......and new doors are $800 IIRC.
Great body work requires attention to detail and patience and lots of practice. If this is the first car you have done then take your time and don't create more work for yourself. Maybe offer free labor at a body shop in exchange for a little knowledge and experience.
one more thing that is huge, glass is real touchy to contaminants(sp), clean surface good first, then do not touch the raw glass once it's ready for the repair, I have seen even just the oil from our skin mess up a repair. I have fixed lots of old vettes, it is supriseing how clean you must keep the raw glass.
Materials
Another valuble supply is 3m 8115.
I ordered the Durablok kit, three(3) rolls of adhesive backed sand paper (80, 120 220 grit), an .8gal of Rage lightweight filler. I also have a gallon of resin, a gallon of reinforced filler, a bag of fg cloth, 3 bags of fg mat (3m from the home depot) and graduated cups, paint sticks, spreaders, cheap brushes and a fg roller. I
Dura Technologies, Duratec Gray Surface Primer 707-002
Evercoat Non-Clog Light Weight Filler
Technique
There is a pot life to epoxy so you do need to move (“apply fairly quick”) but don't rush it.
Check out some of the boatbuilding threads on other forums to learn their technique.
Keep your cuts on the safe side. You can easily cut it long, and then test fit and cut again or file-to-fit. You can NOT easily cut short and then make it longer again. Do not guess on where you're going to make your cuts and drill your holes. Take all the time you need to be sure that the hole you drill or the cut you make is exactly where you want it. One-shot-deal.
I am using the 80grit is used to knock down the flash and do the initial blocking of the gel coat (I have only completed the flash over the rear tires and RH front tire, saving it for after I finish all of the major stuff). I will use the 120grit to block after applying filler to the low spots. The sand paper(summit brand) is 48 times better than the auto parts of the shelf stuff. I've used the same 80grit piece on my long block to knock down the mold flash over the rear fenders and the RH side hood and it’s still like a fresh piece of sand paper. HTHs get you started.
I use Lite Weight products for body fillers. I prefer the "No Clog" but one of the pros I am using likes the Z-Grip. I find the No Clog sands much easier, but the Z Grip goes on and spreads very nicely. Niether ones adheres to wood as well as Bondo or 3M body filler, so I use those where I have wood in place of fiberglass to form a shape for mold making. The Lite Weight fillers are about half the cost of Bondo when you get it by the case from a body shop supplier.
I'm using a high fill primer that is catalized with MEKP. Nasty stuff, same as is used as a catalyst in resins, but is supposed to dry really quickly.
This is one of the better "how to" videos I've found. Unfortunately, there's a bit of bad language in this clip, but I think it's
interesting (from a beginner stand point):