A primer is a chemical substance used to prepare an object for painting or gluing. However, to potato-gun enthusiasts, primer is generally used in the process of combining PVC/CPVC fittings and pipes by preparing them for the gluing process.
How to use Primer
Primer is to be applied liberally to all PVC/CPVC joints, pipes or fittings (by use of a brush) where they are going to be connected together. In many cases, a brush is supplied with the primer. Application of primer should be done immediately before the application of PVC Glue. Most PVC glue manufacturers recommend that the cleaner not be allowed to dry before gluing the joint. As always, the directions on the can provide the best advice on the process of solvent welding.
Health and Safety
Primer is a mixture of methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and acetone. Tetrahydrofuran is a known carcinogen in animals, so primer should be used in a well ventilated area. Gloves can be worn, but care should be taken to avoid spilling primer on them, as acetone penetrates through latex and rubber gloves, where it is absorbed through the skin. In addition, long term exposure of skin to these low-polarity solvents will severely dry your skin out, possibly leading to dermatitis. Swallowing primer may result in death, and chronic inhalation of primer fumes can cause damage to several vital organs including the central nervous system, liver, and kidneys. Symptoms of acute (short term) overexposure include dizziness, headache, nausea, confusion, vomiting, and unconsciousness.
Be sure to read warnings and instructions. For more information the MSDS sheet for Oatey Primer Cleaner is available .
Typical composition of PVC Purple Primer/Cleaner;
|Methyl Ethyl Ketone (MEK)||13 - 17%|
|Acetone||70 - 80%|
|Cyclohexanone||5 - 10%|
|Tetrahydrofuran||1 - 5%|
Types of Primer
There are two basic "types" of building primer commonly used with potato cannons: clear and purple primer(s). The difference is simply that purple primer has a dye added to aid in the enforcement of building codes. This dye is essentially impossible to remove, as it soaks into the pipe fairly deeply. The dye will also stain skin, fabric, wood, concrete, just about everything except metal.
PVC primer is a very thin liquid and will run, drip and splash easily so it is a good idea to protect your work area with newspaper.
Both of these are manufactured by various companies and can usually be found at your local hardware store. Purple primer is easier to see when applied, clear primer can often be hard to detect after in dries. However, purple primer often leads to messy and unsightly purple smears on and around the project you are working on, best prevented by a generous application of masking tape around the non-joint area prior to gluing. Both are equally effective at getting the job done; it is up to you to decide which to use.
Use as a Dye/Paint
The unsightly stains caused by purple colored primer can be made to look less noticeable by covering the rest of the PVC pipe/fitting with primer also. Multiple coats may be necessary to achieve the desired shade. This dyeing method is especially resistant to scratching and was used in this .25 caliber piston valve cannon made by BillyBobJoe of the Spudtech forum.
It should be noted that this rifle suffered a fracture in the rear female adapter, which was most likely caused by an overtightened SCH. 80 plug. The primer only penetrates the surface of the pipe/fitting and once it has had time to dry and dissipate, overall strength of the finished product should not be compromised.
Wikipedia article on primer: