The other day i picked up a damaged oem air dam for the s1 rx8 on ebay. I have the intention of fixing it on the cheapish, well aslong as its cheaper than buying a new one and getting it painted.
The splitter is average condition with expected chips and some scrape marks in the centre. It is however split in two, now ive looked around the internet to see what processes other people go through, it seems that fibre glassing is a common way of repairing bumpers but im looking at seeing if there is some kind of epoxy resin i can use to attach the two pieces together and then sand/fill and attempt to blend.
I dont have a picture right now of the split but one will follow over the weekend, for now i have this:

 

I would try a plastic welder. treat it like steel bevel and then weld it back together. should hold better than fiberglass and it wont crack from different expansion rates of the fiber over plastic.

 

+1 plastic repair will work fine if done correctly.

 

Plastic welder equipment seems expensive, and i dont particularly have the time to learn how to use it properly. I think i will get a quote from a bodyshop before i make the next move. The epoxy resin didnt do a very good job at all, as anticipated. If anything just made a mess of the paint surrounding the split when i tried to remove it.