so i've got my replacement bumpers and i attemped to get the factory baked-on paint off today with very little sucess.
the guy from the custom paint store sold me this "bumper stripper" stuff thats ment to strip the paint off without distroying the plastic, that did very little. then i tried sanding the bumper, all that seemed to do was take the shine off.

anyone done this before? any products recomended or do i have to go down to the panel beater, get them to do it and pay their over-inflated costs?

Sanding should be enough to be able to repaint the bumper, if not pm me for my panel beaters details if you want, he's fairly reasonably priced

when sanding i was using 120 grit with a palm sander, should i go a rougher grit and/or hire an orbital sander?

i'd rather do it myself before i go to a panel beater, both for the money and the 'it's my car, i'll do it' factor...
but from the looks this is something i'm gonna need a pro for.

Not too sure, but should be the same as painting metal bits, ie rough up the surface so the primer has something to stick to, and then the paint to that. Don't think you need to totally strip the bumper of colour, here's my front bar when the car was getting done, looks like it was just given a good sanding:
http://i482.photobucket.com/albums/rr187/mr_cosmo/DSC00170.jpg

Yep, sanding back to smooth/dull is all that is required. AND KEEP THAT ORBITAL SANDER AWAY!!!!Excessive sanding down to the plastic will leave grooves and gauges - the plastic is much softer than the paint and will melt very quickly! Make sure the correct primer/topcoat is used - a flexing agent/additive is needed for many paint types otherwise the paint will crack and flake 3 months later! Done 2 bumpers myself the wrong way and 4 the right way. RESEARCH the proper method for the paint type you use!

Honestly mate, i'd have left the factory paint there and just sanded it back a bit.

in my experience with painting (mostly bike parts, not much car stuff yet) the factory paint tends to stick VERY well and is probably the best primer you will ever get on the surface.

what i've always done is sand the original paint back smooth ( up to about 600-800 grit) and then put your primer (or just paint) on that, you want a nice dull finish to the paint so the new stuff has something to stick to.

honestly though, if i was to paint my bumpers i'd be using primer/filler to get them nice and smooth.
spray on primer/filler, sand back smooth, spray on more, sand back again, and again, until it's perfect.


i'm sure there is a bootload of 'how to paint' articles on the internet, so why not try google and if you find something good then post a link to it. i'm sure others would benefit from a bit of a painting lesson.

i'd write more, but i don't know everything and i'd just be saying what has and hasn't worked for me in the past...

alright, i'll give the sanding a go with the 120 grit,
i got plastic primer and the paint was made up to be the MITSU "WP" colour coded white, with the flexi-resin stuff added to it.

120 grit? I'd be using 800 grade wet and dry!

Paint: Yep - that's the way to go. Use the plastic primer sparingly and all over - takes a while to dry. Make sure the thing is CLEAN before you paint - lots of nooks and ridges for the sandineg sludge to accumulate in! Stiff brush dipped in wax/grease remover works well - wipe with paper towel before it dries! Prep is 99% of the effort needed to do a good job - waving a spraygun around is the fun part. Make sure the back is clean too - crap tends to migrate when the spray hits the front! When you think you have finished painting, get a bright light and look for light-on paint in the hard to get at spots. I bet you will find some! Go slow, be critical - once back on the car any flaws/light areas will annoy you greatly. And - from experience - be prepared to "touch up" any assembly damage. ($20 airbrush works great!)

EDIT: even though the bumpers are a "minor" part of a car, and consume only a small part of the paint required to do a full respray, they are some of the more time consuming items and require the most care in preparation work of any part of the car. A full respray (colour change) takes me 3 months (it's a part time hobby job) and both bumpers take 2 weeks out of that. The cost, money wise, is minimal, the cost labour wise is substancial.

"honestly though, if i was to paint my bumpers i'd be using primer/filler to get them nice and smooth.
spray on primer/filler, sand back smooth, spray on more, sand back again, and again, until it's perfect."

This is the standard approach for steel panels - not a good idea on flexible plastic!

You had better be using the right primer/filler - with flex aid - don't want the stuff flaking off in sheets do we?

EDIT: If your sanding was done with too rough paper you will see many scratch marks through the new paint!
Minimal use of fillers is best - that's why carefull sanding is essential. Minimum use of hand putty (add some flex aid to be sure) is much better.

Just get it sand blasted.

Yes, carefully, and by someone who is experienced!

Bead blasting? A better option, more choice in the abrasiveness of the material being used.

Either one,

Will take someone 5 minutes to strip a bar....and you wont damage the plastic.

I will keep that in mind, for the next time I do a car. Ta!

I have painted more bumpers than I care to think of

If the bumper is painted already and you have not gone through the paint, you do not need plastic primer. As the Magna bumper is a fairly solid bar, you will not need to use flex additive either although it will crack if hit hard, it will need repairing anyway.

The best way is to use an osilating sander, usually air powered. This is what the body shops use. You would usually start out fairly course and work back to finer say 360is. Then you use a primer/filler, hand wet rub and top coats/clear

Paint is actually a lot more flexible that a lot of people give it credit for. Cheap paints will flake off but only if the surface is not prepared properly will it peel.

Pity you are not in Melb, could help you out