Must-do’s when joining plastic pipe

Some types, cements may violate building code
Published on Apr 22, 2011

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For a wide variety of plumbing tasks around the house and yard, plastic pipe is one of the most useful materials you can find. Light, inexpensive and easy to work with, plastic pipe is an ideal material for professionals and do-it-yourselfers alike.

There are actually quite a number of plastic pipes on the market for a wide variety of applications. However, the three most common types that you’re likely to encounter are ABS (acrylonitrile butadiene styrene), PVC (polyvinyl chloride), and CPVC (chlorinated polyvinyl chloride).

All three types of pipe, and the fittings that go with them, are readily available at most home centers, hardware stores and other plumbing retailers.

Pipes and cements

Plastic pipes and fittings are joined together with a process known as solvent welding. A liquid cement actually melts the surface layer of the plastic and fuses the pipe and fitting together. Correctly done, solvent-welded joints are watertight and have more strength than the pipe itself.

Different plastics have different solvent cements that are specifically formulated for use with that material. The cements come in different consistencies — as a general rule of thumb use regular (thin) cements for pipes up to 2 inches in diameter, and medium cement for pipes up to 6 inches.

The cements are also colored, so that when building inspectors are looking at the joints they can readily identify that the proper one was used. Be sure you use the proper cement.

Before using any specific pipe or cement, verify with the building department that it’s approved for the area where you’re using it. Also, don’t use an all-purpose cement, which is not approved by code.

ABS: This black pipe is most commonly used for drain, waste and vent applications (DWV). It’s joined with ABS cement, which is black.

PVC: PVC pipe is white, and is most commonly used for exterior applications such as sprinklers. The cement is usually clear, but you’ll also find both blue and gray for specific applications.

CPVC: This pipe is approved by most codes for both hot and cold water applications. It’s also commonly used for building sprinklers. The pipe is more of a beige color, to distinguish it from regular PVC, and the proper cement is orange.

Primer: Primer is used to clean and soften the surface of the plastic to ensure a good solvent weld. It’s used with both PVC and CPVC, but is not required with ABS. The primer is a readily identified purple color.

ABS to PVC cement: You don’t want to be switching back and forth between these two materials within the plumbing system. However, it’s sometimes necessary to make a connection, such as where the house pipes join those from the city. For that, you can use an ABS to PVC cement, which is green.

Working with plastic pipe

The process of assembling the pipe and fittings is actually pretty simple. First, cut the pipe to the correct length using a hacksaw or a fine-toothed handsaw. It’s important that you cut the pipe end square so that it will seat completely into the fitting; use a miter box if necessary.

You can also use a tubing cutter made specifically for plastic pipe, and there are shears available for easy cutting of the smaller sizes of PVC. Avoid using power saws, since the high speed of the cutting blade can melt the plastic.

Lightly use a knife to remove any burrs on the end of the pipe left by the cutting; don’t use sandpaper. Inspect the pipe and the fitting for damage, and clean them both with a rag to remove any dust and dirt.

For both PVC and CPVC, apply primer to the fitting socket and the end of the pipe, using the brush inside the primer can. Do not omit this step! Next, apply a coating of the proper cement to the end of the pipe and the fitting socket, again using the brush that’s provided in the can of cement. Check to see that there are no uncoated areas.

Immediately join the pipe and the fitting. Press the two together, then twist the fitting slightly to be sure the cement is spread. Hold the two pieces together briefly, until you can see that the cement has set up.

Remember that you need to work quickly, and you’ll get only one shot at completing the joint. If the fitting doesn’t seat correctly, stop! Don’t try to force the joint together, and don’t try to separate it and reglue it. Instead, discard the fitting, cut the pipe back to a clean area, and try again.

Be sure that you read and follow all of the cement manufacturer’s specific instructions for ventilation, cleaning and other safety precautions. Also refer to their instructions for specifics on pipe diameters, application methods and conditions, and for timeframes of when the joint will be ready to use.

Remodeling and repair questions? E-mail Paul at All product reviews are based on the author’s actual testing of free review samples provided by the manufacturers.

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