Each sentence here corresponds with the pic with the same number... 1... Front plastic bumper with a crack. 2... See the crack is open. 3... Drilled 4 holes, tired it closed with some wire. 4... Drill holes 3mm to 6mm either side of the crack. 5... Countersink the holes (I used 12 mm drill). 6... Tape over the crack and holes to stop the fiberglass dripping through. 7... Mix fiberglass resin, put some in the holes and over the area, put on 2 layers of fiberglass mat, cover the mat with the rest of the resin. I used a wooden pop stick. 8... After it's set, remove tape, grind a (V) vee along the crack and expose 5 mm fiberglass from the back. Grind off the paint. Mix more resin, cover the grinded area with it. 9... My resin had sunk in the crack area so roughed it up and put on some body filler. Resin stays liquid too long and ran out the end of the crack. 10... Sand it back smooth ready for primer. 11... Here's the bumper finished and primed ready to be painted.
I'm sure you have to sand back the bumper until there's no shiny areas before painting if i'm correct.. well that's the way i would did it anyway, "unless your just painting the primer area" or go over it with some wax & grease remover. Nice fix those mate, i like your style I did a similar thing with a wing, though this was cracked down the middle inside, ended up bog'd up instead of fiber. Maybe step 12 could be the painted version or a new topic, how to paint plastic bumpers etc?
for a quick touch up, or even a quick (not a pro job) repaint of A panel you should use wax and grease remover, IMS should work too, then a light to moderate sand is required to A clean the surface further B to rough it up a bit and give the paint something nice to stick too, then wax and grease again Thats just my two cents, great post tbh.