Question about front spoiler repair

[chicane]

I have an OEM spoiler (plastic) for a late eighties BMW that I need to repair. It has a medium size crack down the center. These things are quite expensive new so it is worth it to repair and paint. I was wondering how to best provide both the rigidity and the flexibility to keep it strong but prevent cracking in the future?

 

[dude67]

Fiberglass overlay with 2 or 3 ply. on inside to hide repair. About 3 to 4 times larger than crack for strength followed by plastic filler for plastic bumpers. It more flexible than normal.

 

[ToolJunkie]

I just repair mine, wish I took pictures. I did not use any fiberglass. Got tips from a shop that repairs that kind of stuff. (BTW my stuff is an M-Technik2 front valance).
1- Clean the surface with paint thinner. (both sides).
2- 1 tube of plastic welder (Home Depot or Ace). It's a mix (2 into 1).
3- Wood sticks (from Michaels or buy a few ice creams bars like Hagen Daas). or get wood sticks to stir paint usually free at Home Depot. Cut it accordingly.
4- Use duct tape to 'fix' broken section on painted side. just try to get the crack together.
5- Prepare mix, and apply to one side of wood stick (maybe 1/4 by 1 inch) to back side of spoiler. You are trying to apply 'stiches' perpendicular to the crack.
6- Wait for glue to dry.
7- Remove duct tape. You should have a solid piece but with an ugly crack on the front
8- Use a dremmel type tool and make a 'V' notch along the crack on the painted side. Not too deep, just deep enough to spread more glue into it.
9- Prepare more mix.
10- Apply glue to notch. Wait till it dries and sand with coarse grit.
11- Apply more glue to back of spoiler between the 'stiches' (Along the crack)
12- Apply some filler to painted side(not bondo, just some lightweight paste).
13- Wet sand with 400 grit. Primer with SEM flex primer.
14- Admire your work. Should be stronger than new.

Hope it makes sense.

 

[ZRX61]

The FIRST thing to do it find out exactly what kind of plastic it is... There will be a 2, 3 or 4 letter code molded into it someplace: PUR, RIM & PRIM are thermoset, TPO, TEO, PP/EPDM are thermoplastic olefin, SMC, UP, FRP & TRM are fiberglass. There's a bunch more, but that's the main ones.

So whatcha got?