I have seen several discussion on guides and also lots of "How much to re-spray my bumper" and How to repair my damaged bumper threads.
With this in mind I'm gonna try and write up this little job as a guide,
(if the Mods and members in general think it's not worth keeping in guides please move I won't take offence )
I do appreciate that I have the unfair advantage of having a well equipped ZedShed (garage) and hobby level spray equipment, however you could do a lot of this yourself and the prep is labour intensive so if you get it even just ready for primer your onto a winner (it's not hard as my apprentice will demonstrate if he can you can)
So the first thing we need is a damaged bumper BOB? Drive over that speed bump!
He's always happy to oblige
Firstly strip all the bits off - reflectors number plate, grill, canards and anything else Bob has no badges but there are guides on how to remove them.
Next access the damage remove loose and cracked shards of paint and fibreglass, it's better to replace than try and stick it back down with filler of a thin coat of resin (in my experience)
Bob has 3 split in his and where they end right on the edge of the bumper you need to reinforce or it will flex and just crack away.
So I ground out the end of the split to make it deep enough to repair properly
Next clean and sand the inside face where the reinforcing and patching will take place I used a 180 grit sanding disk attachment on an angle grinder (Lightly!!!) it can be done by hand or with a drill attachment.
sand off the loose and split material behind any splits or cracks
Next step is the fibreglass, Available in kits from Motor factors or eBay or as individual packs of resin and hardener and the matting.
Pre cut several patches from the matting and lay near to where they will be needed
Then simply mix the resin and hardener as per the instructions on the tin
1. Most people use to much hardener so it goes off to quick try not too
2. Mix in small quantities it will go off before you finish otherwise so make 2 or 3 small mixes
3. Use old plastic pots (margarine yoghurt etc) and bin them when finished along with a cheap brush
4. Wear latex gloves, save hours of scrubbing
Paint the resin onto the area to be repaired then lay the matting on top (you can dip the matting into the mix but it can be hard to use as it will fall apart) paint generous amounts of resin on top. the aim is to fully impregnate the matting and remove ALL air from in or under the patch.
Build up in layers until you are happy. Don't worry about neatness at this point it is easier to sand back to an edge than try and line up the matting perfectly
work the corners to get the matting all the way in and remove the air
Again building in layers
if it needs to be built up more wait for it to dry and add more - this is a bridge on the end of a split
Then sand back the excess with a course grade paper, I'm using 240 grit paper on the angle grinder but it's easy to go too far with that sort of cutting power!
Then go over it with something a bit less aggressive I'm onto a 320 now
Then to the filler, again plenty to choose from I use an "easy sand" option.
Filler is an art (that I don't have) so the same as the fibreglass mix in small portions and build it up - I'm told lots of thin layers is better than one big thick layer anyway,
Then sand it down, again working through the paper grades we started at a 120 to get the rough shape and very quickly down to a 400
Now sand it again - a block is useful - I'll get a picture for the next post
Second coat of filler and more sanding
Run you finger over the repair - if you can feel a bump or a dip or a little dimple - you will see it in the paint!! You can feel the imperfections better than you can see them at this point!
OK looking good? - SAND IT AGAIN!
OK Then it should now feel smooth and be looking something like this
Now another decision what are you doing? A full re-spray or a blend?
This one is a full re-spray so now the whole front bumper gets the 400 treatment, work the whole area and don't miss the awkward corners, when you think you have it just right - SAND IT AGAIN
FYI we are dry sanding at the moment, we will switch to wet and dry for the final sand before paint.
So that gets us to here -
We will finish the prep and get ready for primer this week so the next stage will follow soon.
Standard Disclaimer -
1. Don't follow this guide!
2. I am untrained, unqualified and have no idea what I'm talking about.
3. If you follow this guide and damage your car in anyway refer to disclaimer line 1
P.S - Sand it again