Ethan Clarke
Solvent welding is a method of joining two pieces of plastic waste pipe together by using a special glue known as solvent weld cement. This process involves applying a chemical to two plastic surfaces with a similar molecular structure, causing the molecules on both surfaces to break apart. When the surfaces are pressed together, the solvent evaporates, and the molecules reform and bond together, resulting in a molecular bond. Solvent welding is often used to join PVC pipes and fittings, creating a permanent joint. The process typically involves preparing the pipe surfaces, applying PVC primer and cement, and holding the pieces together until a strong bond is formed.
| Characteristics | Values |
|---|---|
| Process | Melding two pieces of the same material into one |
| Materials | Two pieces of PVC, PVC primer, PVC cement, gloves, paper towels, pipe cleaner, brush, pipe clips, air admittance valve |
| Procedure | Cut pipe end square, remove burrs, clean pipe, apply primer, apply cement, push pipe into fitting, hold, wipe off excess cement, clean brush |
| Safety | Do not force tightening of the joint, do not let cement sit on skin, do not use on pipes with discoloration/sun bleaching |
| Time | 10 minutes to set, 1 minute to become solid, 8 hours to fully cure, 24 hours before use |
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What You'll Learn
Preparing the pipe and fitting surfaces
To prepare the pipe and fitting surfaces for solvent welding, it is essential to follow these steps:
First, ensure you have the right materials. You will need PVC primer, PVC cement, gloves, and paper towels or clean lint-free cloths. Some sources also recommend using a cleaning solution or a dedicated cleaner for the PVC cement. It is also important to ensure that the fittings are made of rigid PVC and that the sizes and tolerances of the pipes and fittings are in accordance with standardisation.
Next, cut the pipe end square using a mitre block or a PVC pipe cutter. This straight cut will provide a good surface for joining. After cutting, remove any burrs from the cut end of the pipe using a file. This step will ensure that the end of the pipe is smooth and free of any sharp protrusions.
Then, clean the pipe and fitting surfaces thoroughly. Use a dry cloth or paper towel to wipe away any dirt or debris. You may also need to use a dedicated cleaner or cleaning solution, especially if your brand of PVC cement recommends it. A clean surface is crucial for a strong weld.
Before applying the cement, prepare the pipe end further by removing any swarf and chamfering the edge. Use a file or a cutting tool to create a chamfer of approximately 3mm x 45 degrees, or between 22.5 and 45 degrees. This chamfer will prevent the layer of cement from being scraped away when the pipe is inserted into the fitting. It is also recommended to mark the pipe with a felt-tip pen, pencil, or marker to indicate the distance the pipe will penetrate the fitting.
By following these steps, you will effectively prepare the pipe and fitting surfaces for solvent welding, ensuring a strong and secure joint.
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Using a primer
When solvent welding plastic pipes, primer is used to soften the joint surfaces before the application of solvent cement. Although clear primer is available, it is usually tinted purple for ease of visibility. A primer's main purpose is to clean and prepare the surface of plastic pipe and fittings.
To use a primer, open the can and use the attached applicator to cover each surface to be welded on both parts thoroughly. Be careful about runs. If you are doing several fittings, it is fine to prime parts ahead of time, as long as they don't get dirty before cementing. The primer is extremely fast at absorbing and evaporating, so the plastic won't be "wet to the touch" for very long. However, it is important for the plastic to be chemically "wet" with absorbed solvent. Therefore, it is recommended to not let the primed parts sit for more than 5 minutes before cementing.
After priming, you have 5 minutes to apply cement and finish the connection. Waiting too long will affect the creation of a good solvent weld. When applying primer, ensure that you are applying it aggressively to the fitting, the pipe, and the fitting once more, being sure to re-dip between each application.
Primer is not always necessary for solvent welding plastic pipes. For example, ABS pipe is the exception; never use primer on ABS pipe. However, primer is required for ChemDrain systems of 6 and 8 inches.
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Applying PVC cement
Prepare the Work Area and Materials
Before applying PVC cement, ensure your work area is well-ventilated, as the cement releases toxins into the air. If working indoors, keep the door open, or work in a garage or shed. If adequate ventilation is not possible, wear a certified vapor-resistant mask or a respirator to protect yourself from chemical inhalation. Cover your work surface with a tarp or towel to protect it from the glue.
Cut and Prepare the Pipes
Cut the pipe according to your project design. You can use a traditional flat-edged saw, but for better results, an inside cutter is recommended. Smooth the cut edges using a deburring tool or sandpaper to remove any burrs and create a smooth finish. Ensure that the pipe ends are cut square, as this will ensure a snug fit with the fittings.
Dry Fit the Pipes
Before applying any cement, it is important to dry fit the pipes together to ensure a proper fit. This will help you identify any adjustments that may be needed and allow you to mark the pipes for reference. Remember that the receiving socket of a PVC pipe fitting is usually tapered, making it challenging to achieve a perfect dry fit.
Clean the Surfaces
Thoroughly clean the surfaces of both the pipe and the fitting using a clean, lint-free cloth and a suitable cleaner, such as MEK Cleaner. This step is crucial, as any dirt or residue on the surfaces can weaken the strength of the joint.
Apply the PVC Primer
Open the can of PVC primer and allow any excess to drip off. Cover each surface that will be welded, being careful to avoid runs. The primer will chemically react with the PVC, preparing the surfaces for the cement.
Stir and Apply the PVC Cement
Stir the PVC cement thoroughly and quickly. Using a clean brush that is approximately half the width of the pipe, apply the cement to the pipe and fittings. Apply the cement in longitudinal strokes, ensuring that all prepared areas are completely covered. The pipe should have a slightly thicker coat of cement than the fitting.
Join the Pipes and Fittings
Immediately after applying the cement, push the pipe fully onto the fitting without rotating. Twist the pipe a quarter turn as you push it into the fitting to help spread the cement evenly and create a stronger hold. Hold the pipe and fitting securely for up to a minute to prevent the fitting from sliding off.
Wipe Off Excess Cement
As you push the pipe into the fitting, some excess cement may be squeezed out. Wipe away this excess with a clean cloth. Ensure you do this promptly, as allowing the cement to sit too long on un-welded parts can weaken the structural integrity.
Allow the Joint to Cure
Once the pipes are joined, leave the joint undisturbed for at least 20 minutes to an hour before handling it again. The cement will start to dry quickly, but it is recommended to wait 24 hours before using the welded pipes to ensure they are fully cured.
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Cleaning up excess cement
When welding plastic pipes, it is important to clean up any excess cement. If cement is left on the pipe for too long, it can weaken the structural integrity of the plastic. To avoid this, you should wipe away any excess cement with a cloth. Paper towels can also be used to quickly clean up cement, as it does not take long for it to start drying.
If you are wearing gloves, you shouldn't need to worry about cement getting on your skin. However, if you do get cement on your skin, scrub it off. If the cement has dried, it will form a plastic coating that will peel off, similar to a blister.
It is also important to clean the applicator before the cement dries. An oversized applicator may result in excess cement pooling inside the fitting, so be sure to use an applicator that is roughly half as wide as the pipe. After use, clean the brush with MEK cleaner.
Finally, be sure to clean up any surfaces that have been stained by the cement. It can stain everything and will look like a spill.
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Drying and curing time
Solvent weld cement is rapid when it comes to drying and will start going off almost immediately. Most manufacturer variations will be waterproof in around 10-20 minutes and fully cured in about 8 hours. However, it is always recommended to leave the joint for 24 hours before using it.
In some cases, the solvent weld will set fully in about 10 minutes and will be pretty much solid after 1 minute.
In highly humid environments, curing times may increase by 50%. At 100 PSI and temperatures under 40 degrees Fahrenheit, a 1 1/4” CPVC pipe can cure in 2 hours. At 200 PSI, that figure becomes 120 hours, and at 225 PSI, curing takes 10 days.
After about 10-30 seconds, the bond should be strong enough to keep the parts from separating.
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Frequently asked questions
Solvent welding is a method of joining two pieces of plastic waste pipe together by using a special glue that’s known as solvent weld cement.
You will need two pieces of PVC, PVC primer, PVC cement, gloves, and paper towels. You can often get dual packs of PVC cement and primer.
First, cut the pipe end square. Then, remove burrs and clean out swarf. Next, use a pen or pencil to mark the pipe at the distance it will penetrate the fitting. Clean the surfaces of both the pipe and fitting, then apply the cement to the pipe and fittings in longitudinal strokes. Push the pipe fully into the fitting without rotating and hold for up to a minute. Finally, wipe off any excess cement.
You should wear gloves to protect your skin from the cement. You should also be careful not to let the cement dry on your skin as it will peel off like a blister and cause purple discolouration. In addition, do not force the tightening of the joint under any circumstances.
