Although black plastic is a durable and resilient material, it can scratch and gouge when things like rocks and metal pieces rub against it. This can create a rather unsightly appearance in black plastic parts made for the sake of appearance, such as car dashboards. Also these gouges can cause some problems if the black plastic part is needed for a machine's operations and not just for appearances. But rather than replace a plastic part that has gouges, it can be easily repaired with the use of some epoxy putty and a few other materials. Then rather than having to spend quite a bit of money on a new part, you can just spend a few dollars to repair the gouges in the black plastic.
Wet the shop rag in the bucket of water, then wring the rag out. Then apply grease-removing dish soap to the wet shop rag and use it to clean the gouged area on the black plastic. This is needed to remove any dirt and grease in the area of the gouges.
Rub a cotton ball over the area where the gouges are to dry the area completely. Apply rubbing alcohol to another cotton ball and rub that over the area to be repaired to remove any soap residue. Wait for about 15 minutes for the alcohol to evaporate completely. The area is now prepared for the repair process to begin.
Make a boundary around the area to be repaired using the masking tape. Then take a piece of the dark bar and light bar of the two-part epoxy putty, each about the length of the gouge that needs to be repaired. The dark bar of epoxy putty has the epoxy in it and the lighter bar is the hardener. Mix the two bars of epoxy putty in your hand until you get one solid mass and begin to feel heat coming off of the mixed putty. The putty should begin to be a consistent colour at this point. Both bars of the two-part epoxy putty must be mixed well to cause the chemical reaction needed to activate the putty and cause it to begin to harden after about 15 minutes. Now push the epoxy putty into the gouge, filling it. As you do this, smooth the putty into the gouge as much as possible with your fingers. Once you have filled the gouge, wait about 30 minutes for the epoxy putty to fully harden. The gouge is repaired at this point.
Sand the putty smooth with the 600-grit sandpaper.
Apply black paint to the ¼-inch-diameter paintbrush and paint the repaired area to match the rest of the plastic.
Remove the masking tape from the repaired area. Apply rubbing alcohol to a cotton ball and rub the area down to clean off any excess epoxy putty or paint outside of the repaired gouge.
Work as quickly as possible with the putty once you've mixed it because it will begin to harden after about 15 minutes.