FIG. 1 - To join the solvent welding plastic pipe to its fittings, first cut the pipe and then deburr it with a knife.

FIG. 2 - Solvent weld the joint with a cleaner/primer followed by a liberal application of solvent cement to the pipe's end.

FIG. 3 - Next apply solvent cement sparingly to the fitting socket. If the joint is to be pressurized, give the pipe a second application of cement.

FIG. 4 - If you solvent weld a fitting incorrectly, you can saw it out and install the correct fitting. Use two couplings to join the new parts to the old.

SOLVENT WELDING

• The simple solvent-welding process used to join many plastic pipes must be done properly to prevent leaks.
  Here's how.
  
  
• Use the two-step method–employing cleaner/primer and solvent–except with ABS and styrene, with which the one-step method (solvent only) is usually enough.

  1. Inspect the pipe end and fitting socket for cracks, gouges, dirt and abrasion. If the pipe end is imperfect, it can be cut back to expose good material. Discard a damaged fitting.

   

  2. It's a good idea to purchase pipe and fittings made by the same manufacturer. If this isn't the case, test-fit them. The pipe should enter the fitting but meet resistance part-way in. Held upside down, the pipe should not fall off.

   

  3. Cutting pipes. Cut the pipe off squarely to the proper length using a fine-tooth saw or plastic pipe cutter (a hacksaw works well). Flexible plastic pipes are more easily severed with a sharp knife, but be careful not to cut yourself. If you have a large amount of cutting to do, you can get a tubing cutter with a special wheel for use on rigid plastics or a shear-type cutter for PVC. Then, using a knife, remove any burrs and chamfer the outer end of the pipe slightly (Fig. 1). Do not use sandpaper on plastic pipes. It may remove too much material for successful joining.

   

  4. Cleaning. Now, using a quality cleaner/primer, clean the pipe end and fitting socket (omit this entire step with ABS and styrene). Apply the cleaner/primer with a dauber, brush or clean cloth to remove grease, oil and dirt, and to prepare the plastic mating surfaces for solvent cement action. The surfaces to be joined should be clean and free of dirt and grease. The pipe should be dry before applying cement.

   

  5. Solvent welding. Brush on a coat of an ASTM-rated solvent cement that is matched to the type of pipe and fitting you are using. It is important to use the right type of solvent cement. Table B shows the various cements and the kinds of plastic they are suited to. Liberally apply cement first to the pipe end (Fig. 2), then apply it sparingly to the fitting socket (Fig. 3). Leave no bare spots. With chemical-resistant PVC and CPVC pressurized piping, give the pipe two applications of cement–one before and one after coating the fitting socket. With all solvent welding, use a dauber or brush that's at least one-third to one-half the pipe's diameter to apply the cement.

   

   

  6. Immediately join the pipe and fitting full-depth with a slight twist to bring it into correct alignment. The twist breaks up insertion lines in the solvent cement. Hold the fitting on until the solvent cement grabs tightly. A fillet of cement around the fitting indicates that you used enough solvent cement to ensure a leak-free joint. With PVC and CPVC, do not wipe off the fillet. On the other hand, the one-step solvent-welding method for ABS and styrene calls for wiping off any excess cement around the fitting. The joint should be ready for use in an hour.

   

• Safety precaution. Avoid prolonged breathing of solvent cement and cleaner/primer vapors. Work in a well-ventilated area, and cap the cans after each use. Keep solvent and cleaner away from any open flame. Read and follow the precautions that appear on the labels. Remove any cement on your hands with hand cleaner.
  
  
• Correcting errors. Solvent welding is normally a one-way process–you can install the fitting, but you cannot get it off again. When you accidentally put the wrong fitting on a pipe, you must cut it out and replace it with the correct fitting (Fig. 4).