A4 M3 lip spoiler (b5) by sandman
 

i will start off with the usual rating. from a scale of 1-10 10 being real difficult and 1 being easy i gave this project a 4.5. the hardest part is the painting process. i have heard that an auto body shop will paint it for you for around $40-$50. so if youre skittish i would reccomend going this route.

supplies i used,

300, 400, and 600 grit wet sandable sandpaper. (sanding wet is always key)
blow dryer
polishing compound
clay bar
some sort of paint safe marking tool (wax/crayon)

and an assortment of paints. from left to right.
--duplicolor adhesion promoter
--duplicolor wet sandable primer
--audi/VW paint (brilliant black)
--audi/VW gloss top coat

http://img221.imageshack.us/img221/9904/28xk1.jpg

my spoiler came with a weird carbon fiber lookalike film on it so the first thing i did was sand this stuff off, if you dont have this problem simply sand it to rough up the surface so the paint will stick well. i used the 300 grit for this.

http://img221.imageshack.us/img221/2425/17jx1.jpg

once you have bare plastic or have fully roughed the surface its time for the adhesion promoter, add a couple of coats allowing 2-3 minutes inbetween (this stuff drys fast). you will then need to paint on the primer, do this while the promoter is still tacky. after a couple of coats wet sand it with the 400 grit sandpaper, patients is key when it comes to paint so make sure that it is completley dry. paint it with another coat of primer and finish it off with 600 grit. ( if there is still apperant sanding marks at this point sand it with the 400 grit and add another coat of primer, but always finish off with 6oo grit before applying the color coat.)

http://img221.imageshack.us/img221/9674/32yd.jpg

add the color coat, again allow this paint to completley dry and only a couple of coats is necissary, just enough to make sure you didnt miss any spots. (i put some milk caps under the spoiler to keep the edges from sticking to the news paper).

http://img221.imageshack.us/img221/3239/49dt.jpg

once this coat is completley dry its time to add the gloss coat. now this may take practice but you need to make sure the paint is heavy but light enough that it doesnt drip. if its too light the coat will come out spotted.

http://img221.imageshack.us/img221/1999/51so.jpg

this coat will take the longest to dry, i would reccomend letting it dry over night (atleast 8 hrs). now while this is drying you can prepare youre trunk. use the polishing compound to remove all the old wax. then i used some clay bar to make sure the surface was absolutley clear of anything that would keep the tape from sticking, but if you dont have a clay bar just rub hard when using the polishing compound, that should be good enough.

http://img221.imageshack.us/img221/7851/67pt.jpg

http://img221.imageshack.us/img221/2078/76dy.jpg

now that the spoiler is dry place it on the bumper and tape it on in the position that you want it now outline the top with a crayon so you have some guidelines later on (the spoiler may take some bending to fit, if its cold you may have trouble doing this). now slightly heat up the trunk surface with the blow dryer (if its summer skip this step). stick it on and enjoy all the incredible rear downforce you now have LOL.

http://img221.imageshack.us/img221/2726/86kg.jpg

it looks so good that the spoiler paint looks better than the paint on the trunk.