Tape The Damage Together From The Front Side
Use masking tape to hold the cracks together. Do not try and apply the resin between the cracks as this will distort the box. Taping the damage together as tightly as possible will keep the shape while you begin the repair from the back side.
Remove Any Dirt, Grease, or Paint From The Back Side
Remove any dirt, grease, or paint from the back side. You need to get down to the raw plastic. The resin will melt into the plastic and bond the new ABS in the resin to the box. The resin cures in about 24 hours to a hard finish the same as the original plastic.
Apply The Resin Directly From The Applicator Bottle.
Apply the resin directly from the applicator bottle. There is nothing to mix or add. The resin will flow out and smooth as it cures. The resin is about the same constancy as thick yogurt and will stay where you put it. You can apply it upside down or on vertical surfaces and it will stay in place. The resin cures in about 24 hours and turn rock hard.
Continue The Repair From The Front Side
Remove the tape from the front side. I use a Dremel Tool to groove into the cracks. You can also use a knife or file to make the groove. Groove out 50% to 75% into the plastic.
Fill The Groove From The Front
Fill the groove with resin from the front side. You want to fill the groove completely, do not over fill as you will sand the repair. You can add more resin if needed after the first application is cured. Apply the resin directly from the applicator bottle. There is nothing to mix or add. Let the resin cure for about 24 hours. When the resin is rock hard you will know the resin is cured.
Sand The Repair Smooth
Sand the repair flat an smooth with the surrounding plastic. Do not use any two part bondo type fillers to even out the repair. This material will not stay bonded to the plastic and will crack and flake off. Use the same resin as a filler it will weld in place and never come out. In this case the Tule Box was painted a metallic black and I was not going to repaint. I masked the area around the repair to limit the amount of area sanded. There will be small air holes in the resin this is normal. Prime the area and if needed use a single part spot putty to fill the air holes. You can find the spot putty at any automotive store that sell auto-body supplies.
Finish The Repair, Final Sand, And Paint
The repaired area will sand and accept pain the same as the original surface because it is the resin is the same ABS plastic. Trying to repair plastic with any epoxy type product will not sand smooth because the Epoxy is so much harder than the plastic. In this repair the original paint is impossible to match and i did not want to repaint the whole box so I limited the area affected and had a local sign shop make a vinyl flame graphic to cover the repair.