tbh if your new to this stuff its something which has gotta be done properly and effectivly or it WILL crack.
im currently fitting a rear defuser to an astra gte rear bumper which is off another car.
to start with you wanna line it all up, make sure it fits, its snug etc etc.
drill a hole straight through the side of your splitter and your bumper and screw in a self tapping screw. (use 1/8 or 3/16 drill bit)
do it the same for the other side.
do about 3 or 4 more self tappers on the front of the bumper thats facing you.
check the allignment, make sure your happy with the position.
undo all your screws and drop the splitter off, now, where your holes are in the splitter, you need to carefully get a big drill bit , (this size of the head of your screws) and just drill slightly into the splitter.
this creates an indent, so that when the screw is tightened upto the splitter and bumper, the screw becomes countersunk.
now get some bonding addhesive (i only recommend sikaflex) and run a pretty thick bead all the way along your splitter on the inside, quite a bit at the ends, and wherever you think it will touch the bumper and hold it securely.
put back in all of your screws so its nice and flush with the bumper and leave the sikaflex overnight to let it go off properly.
next you wanna check your screwheads, if any are sitting proud to the splitter and stick out a bit, then simply grind the heads off a bit with a grinder or whatever you got handy, possibly a dremmel.
now for the prep work.
all along your splitter at the top and where the bumper meets the splitter, give it a good scuffing up with around P80.
i generally try not to use P80 on plastic as it makes it "furr up" but were working with large areas of fibreglass and filler so its fine.
give these areas a good rubbing down with your P80 sandpaper.
mix up your fibreglass with your hardener, generally use about 3-5% hardener, and give it a nice skim right the way along where the splitter meets the bumper, push it right into any gaps, give it a good push down then smooth it off.
dont use too much as its a b**ch to rub down and a pain in the ass to work with, keep it to a minimal if you can but giving it as much protection from cracking as possible.
let this dry, then, if you have a sander, sand it all down so its smooth with P80, so youve got the general shape of how you want it smoothed in.
extend the prep with P180, basically where yourve sanded your fibreglass and youve sanded the plastic and splitter, sand it a few inches more to give the filler something to key to.
next you want to mix up some filler (easy-sand) again generally 3-5% with the hardener, then smooth it all over your fibreglass so its covered and smooth it into your bumper too.
fillerwork comes with practice and not something that you'll master quickly, ive been doing fillerwork a good 7 years and theres jobs that still test me to the full and can take me hours and hours on end.
once your fillers dry, you wanna start rubbing your filler down with P80.
now, for the sides of your bumper, you want it flat, so use a rubberblock with your P80 sandpaper to get it as flat as possible and also smoothed in properly.
as for the frunt, im guessing its gonna be a slightly rounded shape. so a rubberblock is no good for this as it will just take chunks out of places you dont want them taking out of. for places like this, find something that fits into the general shape of the curve, i generally grab a can of primer or a tube of sikaflex, wrap the sandpaper around it and use that to sand it down to a curve.
trial and error, just keep sanding areas that need sanding, applying more filler where needed, sand to your hearts content til your happy with the finish.
sand it all over again with P180 to get rid of ALL the deep scratches then sand it all again with P320 to get rid of those scratches.
dont cut corners, get rid of ALL the big scratches, if you dont, the primer will sink, the paint will sink, the laquer will sink and it will look a right dogs dinner.
once its all dry sanded with P320, i highly recommend giving it a good wet flat with P800. this gets rid of all the "furring up" i talked about earlier. give the entire bumper a wetflat with P800-P1200, this will act as a key for the paint (basecoat colour) but also smoothes out your old laquer for a nice flat surface.
once its all sanded, wet flatted, dried and cleaned, you are now ready to primer it.
i wouldnt really recommend using aersolos as youve worked with fibreglass, filler, been using P80, so ide say from there, take it to a bodyshop and get them to primer it for you with 2K primer.
alternativly if you have your own compressor, spray it up yourself.
you'll need 2k primer and 2k hardener.
also ide advise getting some thinners to clean your spray gun afterwards.
as for the crack, i dunno how big it is, where it is etc, get pics up and we can determine at what stage you should repair it, whether you do it before the splitter gets stuck on, or while your fibreglassing it into the bumper.
*this is a general guide, dont flame me, obviously people have different ways of doing things, this works for me**
Things You'll Need
- P80, P180, P320 dry sandpaper
- P800 or P1000 or P1200 wetordry sandpaper
- fibreglass
- filler
- sanding block
- sikaflex bonding addhesive
- drill with drill bits
- screws
