I have 2 cracks in plastic i would like to fix. 1st, is in the interior somewhere on one of the panels. It is a small crack where the piece broke into 2. I have tried Plastic epoxy as well as jbweld, both cracked soon after again. I applied the products right too. Roughed up, cleaned with acetone, applied to both surfaces, held together for 24 hours untouched.

I also have small cracks all the way through my fenders on the bottom. I tried jbweld and it didnt even seem to stick at all. Both crack again.

Is there any proper way to fix cracked plastic. I would like to fix my fenders, sand it down and do touch ups.

 

I've never done it nor do I know exactly how it's done, so don't quote me on it. But I heard you can use fiberglass, and it comes out looking perfect.

 

Repairing interior plastics can be difficult. You need to know what type of plastic you are dealing with. Knowing that will help determine the material choice for the repair. It may be easier to look on e-bay to find a replacement panel.

If you can tell me which panel you are attempting to repair, I'll look in my shop manuals to see what plastic you have. I'll also need to know a little more specific info on the extent of the damage to help diagnose the fix.

I haven't researched it yet, but I believe the fenders are made of SMC (sheet molded compound), a paste blend of polyester resins an chopped glass fiber. That is a little easier to fix:

Materials needed:
*assorted grit sandpaper
*polyester resin and catalyst--available at Wal-mart, home depot, autozone etc.
*fiberglass (cloth preferred, mat if you can't get cloth)
*cheap disposable paint brushes
*bondo or similar body filler

Ideally, you need access to both sides of the area to be repaired. Thoroughly clean the interior and exterior surfaces with isopropyl alcohol, not acetone. Acetone can leave a residue that can affect the adhesive bond. Inspect the damaged area carefully to determine how much area needs to be sanded away. Sand the non-critical (for cosmetic purposes) side first. remove all traces of loose material (including all traces of previous repair material) until the surface is nice and solid. When you are finished sanding on this side, the sanded area should be about 2" larger than the damaged area in all directions. Again, thouroughly clean the surface with alcohol. When all traces of alcohol have evaporated, brush catalyzed resin over the entire sanded area. Cut pieces of fiberglass that will fit the repair area--4 or 5 layers. Place the fiberglass patches one at a time, wetting them thoroughly before applying the each subsequent layer. Use only as much resin as what can be absorbed by the fiberglass. Too much will make the repair weak. The fiberglass provides the strength for the repair, not the resin. NOTE: Polyester resin, when properly catalyzed and well mixed will cure quickly, so work with small amounts. Allow the patch to cure completely befor proceeding.

When the first side is cured, start sanding the side that is the cosmetically important. Taper sand the area around the damage. The area should "V" thinner toword the damage, removing all loose material--as done on the first side of the repair. Clean with alcohol and allow to dry. With this side being more cosmetically important, you need to test fit your dry glass patches for fit. Ideal fit of your patch layers should start small at the center of the damaged area and progressively get largeras the hole is filled--looking like the rings of a bullseye target. Wet the surface with resin, place the plies of fiberglass one at a time--just like explained on the previous side. When everything is cured, sand as required to obtain the desired surface contour. Fill any pinholes with bondo or similar material. The coat of bondo should be a very thin skim coat. Multiple thin thin thin layers may be necessary to get it right. Bondo adds no structural integrity and will crack if put on too thick. Finish sand, and paint as required.

Another note, you can speed the cure of the resin by putting a little heat on it--like a hair dryer, not any hotter. Allow the resin to cure to the consistency of hard cheese at room temperature before adding heat or you will blister the repair.

Good luck. If there is anything I was not clear on, ask.

 

I've fixed several cracks in my plastic interior with an epoxy called plastic welder. They sell it at walmarts. It says its rated up to 3500psi. Which i don't believe but its really strong. When my dash pad started cracking in the corner. I pulled it off and sanded the under side of it. Then used the plastic welder on the back. I then took a coat hanger and cut it up into little bars about 2-3 inches long and put them in the plastic welder epoxy and covered them up. I have them running perpendicular across the crack. They work as reinforcement. The dashpad is as strong as new and has kept the crack from continuing across the pad.