Article written by: Jason Danaher Ph.D.

This tech talk will introduce the process of identifying and joining polyvinyl chloride (PVC) pipe using primer and cement. Plastic pipe made of PVC is commonly used in aquaculture applications to contain and direct the flow of untreated or treated water and pressurized gasses in and around the production system. There are two types of PVC pipe (Table 1) applicable to aquaculture and the main difference is wall thickness expressed in “schedules”. The pipe schedule is abbreviated as SCH. 

The first common schedule pipe used in aquaculture is SCH 80 PVC pipe. It is highly durable, has high tensile and impact strength, and is resistant to many corrosive chemicals like ozone.  Schedule 80 PVC pipe is usually dark gray in color and has a thicker wall compared to Schedule 40 PVC. The thicker wall allows SCH 80 PVC to handle higher pressure ratings for fluids or gasses.

Schedule 40 PVC pipe is white in color. It also is durable, but it cannot handle corrosive chemicals like ozone and the pressure rating for SCH 40 PVC is reduced because it has a thinner wall compared to SCH 80 PVC. Nonetheless, SCH 40 PVC pipe is commonly used for aquaculture plumbing components because it is less expensive, and its characteristics satisfy many scenarios encountered in aquaculture applications. 

Table 1. Characteristics of Schedule 80 polyvinyl chloride (PVC) and Schedule 40 PVC.

There is another type of ‘white colored’ PVC pipe used for drain and sewer line applications. This pipe is known as PVC Drain Waste and Vent (DWV) and is lighter in weight and has thinner walls compared to SCH 40 and SCH 80 PVC (Figure 1). 

Figure 1. Visual comparison of same sized diameter polyvinyl chloride (PVC) pipe to show differences in wall thickness for PVC DWV, SCH 40 PVC and SCH 80 PVC. 

The PVC DWV should not be used to move pressurized gas or liquid in or around an aquaculture system and typically is avoided all together for aquaculture applications. Markings on the pipe can help identify the schedule. The text printed directly onto the pipe surface for identification and quality control purposes is referred to as the "PVC print stream" which includes details like the pipe size, material type (PVC), schedule (e.g., 40, 80), manufacturer's name and production code. Each manufacturer is different, but below is an example of how manufacturers mark PVC pipe and what to look for (Figure 2).

Figure 2. Example of potential markings on the surface of 3.0-inch diameter, schedule 40 PVC pipe to identify the size and type. 

Note:  Each manufacturer marks their pipe differently. There is no standard print size, format or order to display text.

Whether it is SCH 40 PVC or SCH 80 PVC, connecting the pipe together requires proper “slip” fittings and specially formulated primer and cement. A slip and socket fitting refers to a PVC connection with no threads or barbs and simply goes over the end of a pipe. Different sized socket fittings have specific depths the pipe must be inserted to form a strong joint. A slip or socket fitting requires PVC primer and cement to join the fitting and pipe together.

The PVC primer is a low viscosity, chemical solvent applied to the surface of PVC pipe or the inside surface of PVC fittings before applying cement. The primer is a crucial component to ensure your pipes and fittings are appropriately prepared for a secure and long-lasting connection. When the primer is applied to the PVC and allowed to dry, the solvents in the primer help to slightly dissolve the outer layer of the PVC pipe or fitting. This chemical reaction establishes a rougher surface that allows the cement to fuse to the surface more effectively. 

PVC cement, also known as solvent cement or "pipe glue," is generally a medium viscosity, chemical adhesive specifically designed for joining PVC pipes and fittings. It melts the plastic and fuses the individual components together with a durable, airtight and waterproof bond. The cement is applied to the surface of PVC pipe or the inside surface of PVC fittings after applying the primer and allowing the primer to dry. 

The basic process of preparing and cementing PVC pipe involves the following steps:

1. Clean the pipe with a clean rag or brush to remove any dirt, dust, or debris.
2. Apply primer to the outside of the pipe and the inside of the fitting to clean and prepare the PVC surface of each.
3. Allow the primer to dry for about 10 to 15 seconds after application.
4. When the PVC surface no longer appears wet and the primer has dried, then apply an even coat of the cement to the same area where primer was added on the pipe and fitting.
5. Insert the pipe firmly into the fitting, give it one-quarter turn and allow the cement to begin the drying process.
6. Maintain pressure on the cemented joint for a minimum of 30 to 60 seconds while the cement starts to dry and does not retract from the joint. The time required is dependent on the diameter of the pipe and also the type of PVC fitting used at the joint. If the manual pressure is not maintained after cementing the joint then the end of the pipe will push away from the fitting in the opposite direction and the bond will be lost or severely weakened.
7. It is recommended to allow at least 24 to 72 hours for joints to cure before pressurizing the plumbing with water or air and checking for leaks. Refer to the manufacturer’s product label for a specific cure time.

The process of joining PVC pipe and fittings with primer and cement is relatively simple, but also pretty easy to do improperly. Even the most skilled plumbers and “jack of all trades” have made mistakes when cementing PVC plumbing. Unfortunately, if you do make a mistake, you’ll have to cut out the pipe and fitting and then start over which wastes time and money. The mistakes often happen when the facility is located a long distance from hardware stores, occurs with specialty fittings not often inventoried in nearby hardware stores, or transpires after hours when nearby stores with inventory are closed. In short, plumbing mistakes happen at inconvenient times. The proceeding information will hopefully minimize mistakes from happening.

Choose The Correct Type of Cement and Primer.

Read labels carefully and be sure to select cement made specifically for PVC as there are different kinds of cements (and primers) on the market formulated for various types of plastic piping. The pipe cements and primers are specific to the pipe material you are working with and not all are interchangeable. A common brand of PVC cement used for SCH 40 PVC pipe is Oatey and can be found at most hardware stores (Figure 3). 

Figure 3. Oatey, a common pipe cement and primer available for plumbing Schedule 40 PVC pipe.

In addition, to cements made for different types of plastic pipe, there are also formulations designed for certain applications. Refer to the product's label to identify its intended use (i.e. quick drying, underwater or damp installation).

Furthermore, the primers come in two different colors: purple and clear. Purple primers are used in industrial applications to expedite the visual inspection process of the plumbing. The purple color may not be aesthetically pleasing and can appear “messy” compared to clear primer. Clear primer may be a preferred choice if the PVC pipe will remain exposed and local code allows for its use. The shelf-life of most unopened PVC primer and cement is 2 to 3 years from the product’s manufacturing date and can be found printed on the container or its packaging. 

Dry-Fit Your Pipe and Fittings Before Cementing.

Always take the time to dry-fit your components before applying any primer or cement.  Dry-fitting allows you to verify the alignment of plumbing and make sure the PVC pipe was cut to the correct length that you need so everything fits appropriately. Skipping this step can lead to misalignments and measurement errors, resulting in water or air leaks and weak joints. The universally recognized truth in all construction projects, “measure twice, cut (and glue) once” encourages careful first steps in plumbing to avoid extra work later.

Identify and Follow Safety Warnings.

Plumbing PVC pipe can quickly result in a messy work environment. Placing a drop cloth over your work surface can help to minimize difficult cleanup in the event of primer or cement drips. The viscosity of primer and cement in combination with the application technique can result in splashing. You should wear safety glasses and nitrile gloves to avoid eye and skin contact. The work area should also be well-ventilated with fans directing airflow towards open windows or doorways leading to the outside. The PVC pipe primer and cement can emit harmful toxins and inhaling the fumes can irritate the respiratory system, leading to symptoms such as coughing, shortness of breath, and chest discomfort.

Confirm The PVC Pipe Is Cut Clean.

There are several tools used to cut PVC pipe and the choice of which tool to use is often dependent on availability and the pipe diameter you are working with at the time of plumbing. Having a combination of tools available will prove useful because you will find yourself working with a variety of pipe diameters at aquaculture facilities. Common tools include:  a PVC cutter, fine-toothed handsaw or hacksaw, and miter saw (Figure 4). 

Figure 4. Images of a PVC cutter (left) and miter saw (right) commonly used to cut Schedule 40 PVC pipe.

The advantage of the PVC cutter is it makes a clean cut without leaving burrs on the PVC pipe compared to the handsaws or the miter saw. Saws always leave burrs that appear along the cut ends of the pipe and on the inside due to the friction caused by the tool. Be sure to remove any burrs from the edges of the cut surface with a utility knife or deburring tool (Figure 5). Deburring tools like those pictured in Figure 5 are also used to bevel, or angle, the PVC pipe end to ensure it slides into the socket fitting well.  

Figure 5. Images of commonly used hand deburring tools to remove burrs leftover from cutting Schedule 40 PVC pipe.

Burrs can be problematic because if they are left in place they can catch debris flowing through the pipe, resulting in future pipe clogs, or compromise the integrity of the cemented joint by interfering with bonding the two surfaces you are trying to join together.

Work Quickly, But Carefully.

It is not recommended to prime multiple, individual pieces of pre-cut PVC pipe before cementing together because it could affect the quality and strength of the bonded joint. It is recommended to prime and cement each joint one at a time. Immediately after applying the primer and allowing it to dry (10 to 15 seconds) you need to apply the cement evenly around the exterior perimeter of the pipe surface AND the interior surface of the fitting. Applying the cement to both surfaces may sound redundant, but it ensures an even coat is applied across the entire surface where the joint is to form. 

The female end is represented by the inside of the PVC fitting and the male end is represented by the PVC pipe end.  Primer should be added to the female end of the joint first and then to the male end of the joint. Next, the cement should be added to the female end of the joint and then to the male end. This order is important because of the way pipe and fittings are tapered to accept one another in forming the joint and because of the way the primer and cement prepare the surfaces for bonding.  

Proceed quickly when cementing PVC pipe; if the cement begins drying before you’re ready to insert the pipe into the fitting then reapply the cement to both surfaces. If the cement has completely dried because of a time delay or high ambient temperature, then the pipe and fitting cannot be used and must be replaced with a newly primed pipe end or fitting to ensure a quality joint is formed after new cement is applied to the prepared surfaces.

After applying the cement, you will immediately insert the pipe into the fitting. “Old school” plumbing rules suggest you should quickly apply a quarter turn twist as you push the pipe into the fitting. This allows the cement on both surfaces to blend, and the twisting will allow the softened surface of the two PVC surfaces (pipe + fitting) to increase contact area while bonding and result in a tighter and stronger bond. However, theoretically you do not need to provide a quarter turn if you prepare the pipe and fitting properly beforehand by applying primer and cement evenly on the surfaces and have removed all burrs from the inside and outside of the pipe. 

Whether you twist the pipe in the joint after inserting or choose not to twist, you must continue to apply firm pressure on the cemented joint for at least 30 seconds. Lab analyses have determined over the entire bonded surface of a PVC pipe contributing to the overall joint strength, the majority (85%) of the bonding force actually occurs within the first 15% of the pipe's surface area where it makes contact with the fitting. This stresses the importance of a  proper insertion depth and maintaining pressure for a strong connection.

Allow Sufficient Time After Cementing for Joint to Bond and Strengthen.

After holding the pipe in place for 30 seconds it will feel nearly impossible to manually twist or pull the joint apart. Don’t be fooled. Before repositioning the newly cemented plumbing, it is recommended to not disturb the joint for an additional 20 to 30 minutes if working with pipe diameter less than or equal to 3-inches (7.62 mm). This allows the cement to set and cure properly to a specific pressure rating. Set time refers to the time it takes for a cemented joint to become firm enough to handle without disturbing the connection, while cure time is the longer period needed for the joint to reach its full strength and be ready for fully functional design pressure. Manufacturers of PVC primer and cement have recommended set and cure times for  their products which is dependent on type of plastic pipe, diameter of pipe, ambient temperature and humidity. 

If the fitting you are connecting the pipe to has multiple joints (i.e. coupling, elbow, tee) it is ok to continue connecting the pipe to those remaining joints while the first one is curing. You should refrain from bending, torquing, or dragging recently cemented plumbing to another location immediately after cementing. If the joint is suspended, you should support it to keep it from bending or torquing before fully cured. It is best to allow the cement to cure and dry for at least 24 to 72 hours before implementing additional quality control checks for water or air leaks. 

In conclusion, you should now have the basic concepts required to understand good PVC plumbing techniques for your aquaculture facility. Learning to install or repair existing plumbing at an aquaculture facility requires skill and patience. Oftentimes the first project or two become great learning opportunities! Shadowing and practicing the basic skills discussed above under the supervision of a professional and/or experienced plumber will quickly advance your knowledge with cementing PVC pipe and fittings. In addition, the American Society of Mechanical Engineers (ASME) provides a solvent-welding certification course for interested individuals who work cementing PVC plumbing together on a regular basis.