Once you have gone all the way around with the fiberglass cloth and covered the areas of the grill, now run a bead of the problem plastic repair on top of the fiberglass cloth and smooth it out. Once this dries sand it down. Shape body lines and smooth out the surface. You should no gaps and so seams just a smoothed grill now.
You will have to use some glaze to skim the surface before you primer and paint the bumper, but at this stage the hard work is done.
Now if you want to ensure the grill does not ever crack flip the front fascia over and place on a stand and repeat the process on the back side. The back side does not need to be pretty because you will never see it.
Here are some pictures.. Remember to sand all areas good with 24 roloc grit and a grinder, also use a DA with 40 grit to get into tight areas. You must sand inbetween each coat of problem plastic repair.
