Identifying Your Plastic

Short of a full lab test, it would be difficult to actually identify a plastic since many have special additives and may even be mixed plastics. But, here is a simple test and a few tips to see if Plasti-Mend will work on your application.
 Since Plasti-Mend works only on solvent reactive plastics, the easiest test is with a solvent. The best solvent for this is the PM Thinner since it is the solvent used in Plasti-Mend products. One of next best solvents for this test is MEK or Methyl Ethyl Ketone. MEK can be obtained at your local hardware store and is also a major solvent in many lacquer thinners. You can also use a clear ABS, PVC, CPVC plastic plumbing cleaner. It has a mix of solvents, including MEK, that works quite well for this test as well as a prep for use of Plasti-Mend. Acetone by itself is not a good solvent to use for this test since it works too slow.
Take some solvent on a cloth, dauber or “Q-tip” and rub the plastic you want to test.  Use enough solvent to get the plastic wet.  If the plastic is solvent reactive, a small amount of the plastic will begin to dissolve, transferring to the cloth or dauber. It may take a minute or two for the plastic to begin to react depending upon the type of plastic. ABS will react within a short time. If the plastic shows signs of reaction to the solvent the Plasti-Mend products will work.
 Plasti-Mend contains solvents that are “hotter” than the cleaner or MEK so there are some plastics, such as acrylics and polycarbonates, that these solvents will have little effect on that Plasti-Mend will still work on. Many acrylics are the clear and transparent colored plastics that many people know by the brand name Plexiglas.
Polycarbonates can be any color but they are usually considered "unbreakable" due to their high impact resistance.
For RV holding tanks, one of the quickest and easiest ways to see what plastic you have is to look at the pipe connection coming out of the tank.
If the pipe is glued into the tank fitting, the tank will be ABS and Plasti-Mend will work fine for any repairs.
If the pipe is clamped or screwed into the tank, the tank will be Polyethylene and Plasti-Mend will not work on it. The only reliable repair for the PE will be themal welding.
 ABS tanks are thermoformed, usually of 1/8 inch sheet plastic. They will normally have a mounting lip around the top that the top sheet of the tank is glued on to.
If the pipe is clamped or screwed into the fitting, then the tank is polyethylene or other non-reactive plastic. It will be clamped because no glue or adhesive will work on these plastics. Any repairs should be with thermal plastic welding.
 Most polyethylene holding tanks are a milky gray to gray black and will be 1/4 to 3/8 inch thick, much thicker than ABS. Poly tanks are normally molded in one piece so mountings will be molded as part of the tank.
 Fresh water tanks are usually made of natural polyethylene, a milky clear plastic. Any black fresh water tanks will normally be ABS.
 Fuel tanks are not made of solvent reactive plastics since many additives and solvents in the fuels would melt or degrade the plastic. Most fuel tanks are polyethylene although some other plastics may be used.
ABS sheet plastic that many items are made from will usually have a "haircell" texture on one side. This is like an orange peel texture made to simulate leather. Most of the hard plastic interior trims on cars, trucks, boats and aircraft is ABS plastic with this texture.

A Typical ABS Plastic Holding Tank

Note the lip aroumd the top of the tank used for mounting. On the Polyethylene tank shown, the mounting is the wide formed ledge seen on the side or end of the tank.

A Typical Polyethylene Holding Tank

Note the mounting ledge on the side or end of the tank versus the lip on the top of the ABS tank. The fitting on the tank will be the same type of plastic as the tank although it may be a different color. The drain pipe will be clamped or threaded into this fitting.