Common Solvent Welding Mistakes

Creating a perfect solvent weld is an important skill that will come in handy while working on PVC, ABS or CPVC plumbing systems.

What is a solvent weld? When you join PVC, ABS or CPVC pipes and fittings, you aren’t gluing them together. (You’ll often hear solvent cements referred to with terms such as PVC glue, pipe glue, cement glue, plumbers glue, etc., but these terms are actually incorrect.) Instead, the pipe and the fitting are softened and chemically fused together creating one piece. Once they are joined, they cannot be taken apart.

Watch the video below for a simple tutorial on solvent welding. In addition, be sure to avoid the common mistakes listed below in order to get the best results.

Not choosing the right cement for the job

Make sure you’re using the right cement for the job based on pipe material, pipe size and job conditions. If your project uses CPVC pipe, be sure to use CPVC cement. For PVC pipe fittings, use PVC cement. For ABS pipe fittings, use ABS cement. If you use the wrong cement, you won’t create the weld you need.

Solvent cements should also be selected based on the pipe size. The larger the pipe, the thicker viscosity you need. For example, if your pipe is 6” in diameter, you can use medium body cement, but if your pipe is 8”, you should be using a heavy body cement. You can find the maximum recommended pipe size listed on the cement can. Finally, make sure that your cement is rated for the conditions of the job site. If you know you’ll be working in temperatures below 40°F, select a cement that is formulated to fully cure in those temperatures.

Similarly, if you’ll be working in wet or damp conditions, it’s important to choose a cement that is formulated to cure in damp conditions. You should also consider whether you’re working on a potable water system or a non-pressure DWV system and select the correct cement for that application.

Not preparing the pipe properly

Preparing the pipe properly before making a solvent weld helps reduce the opportunities for failure to occur. To properly prepare the pipe, you must:

• Cut the pipe square – This ensures maximum surface area to create fusion and joint strength, ensuring the strongest bond.
• Deburr the pipe – If you don’t deburr the pipe, pieces of plastic can break free and move through the system, which can lead to blockages in items like aerators. Burrs can also catch certain types of debris which could eventually lead to a blockage in the DWV system.
• Chamfer the pipe – If you don’t chamfer the pipe or bevel the outside edge, the sharp edges can scrape the cement off the walls of the fitting as the pipe is being inserted. This could potentially cause a blockage or leak paths.
• Clean the pipe – Make sure there’s no dirt or grease that may interfere with the cement’s adherence to the pipe and reduce its ability to create proper fusion and joint strength or scrape the interior of the fitting creating leak paths.
• Test the interference fit – Before primer or cement are applied to the pipe or fitting, ensure there’s resistance at 1/3 to 2/3 into the fitting hub, to ensure a good interference fit. The fittings are slightly tapered and designed to fit together very tightly. If the pipe and the fitting are not a good match, it can lead to a weak joint, pipe separation or a poor bond.

Skipping primer* or applying improperly

Primer must be used to create a solvent weld on PVC and CPVC pipes. The solvents in primer soften the pipe and fitting, making it more porous and allowing the cement to form a stronger bond. When applying primer, ensure that you’re applying it aggressively to the fitting, the pipe, and the fitting once more, being sure to re-dip between each application. Once you have primed the pipe and the fitting, you have 5 minutes to apply cement and finish the connection. Waiting too long will affect the creation of a good solvent weld.

*ABS pipe is the exception; never use primer on ABS pipe.

Not waiting the appropriate set and cure time

After the joint is assembled, it should be left undisturbed for the recommended set time period. Set time is the amount of time needed for the joint to achieve the strength required so that the bond is not compromised if small movements occur.

Cure times are based on pipe material, pipe size, ambient temperature and humidity. In humid areas, allow 50% additional time for the solvent weld to fully cure.

View our overview document for more information on all our cement offerings and their cure/set times.

Not having adequate airflow

For the same reason you need to wait the appropriate cure time for your project, there needs to be airflow in the plumbing system where you’re completing your solvent weld. Without adequate airflow, the solvent will not be able to evaporate. This could lead to pipe or joint failure as the solvents continue to soften the pipe and fitting surfaces.

With our tips for creating the perfect solvent weld and knowledge of how to avoid common mistakes, you’re all set to create long-lasting, leak-free connections.

Guest Author: Erin Bullock is Applications Manager, Oatey Company. He can be reached at technical@oatey.com