Can you connect PVC to ABS?

PVC (polyvinyl chloride) and ABS (acrylonitrile butadiene styrene) are two of the most common types of plastic pipes used in plumbing systems. Both offer advantages such as durability, corrosion resistance, and cost-effectiveness. However, there is an important difference between PVC and ABS that affects whether and how the two can be connected. Specifically, PVC and ABS are incompatible plastics with different properties that make joining them directly problematic.

In general, plumbers recommend avoiding connecting PVC and ABS piping. But there are certain transition methods that can allow you to switch between PVC and ABS if necessary. Understanding the differences between PVC and ABS and the limitations on connecting them will help you decide when it’s possible or advisable to transition between the two in a residential or commercial plumbing system.

The Differences Between PVC and ABS Pipes

PVC and ABS have different chemical compositions that account for their distinct properties and compatibility issues when joining them together:

PVC

– PVC stands for polyvinyl chloride plastic.
– It is made of vinyl polymers with chlorine atoms.
– PVC has high tensile strength but low ductility. It is rigid and can be brittle.
– PVC is naturally white in color but can be dyed grey or black.
– It has a high resistance to chemicals, weathering, and abrasion.
– However, PVC on its own has poor impact resistance. It becomes more durable when combined with impact modifiers.
– PVC has a high heat distortion temperature of 140°F, making it suitable for hot and cold water plumbing.
– Chlorinated PVC (CPVC) has increased heat resistance for temperatures up to 200°F.

ABS

– ABS stands for acrylonitrile butadiene styrene plastic.
– It is made from styrene polymers combined with acrylonitrile and polybutadiene rubber.
– ABS has higher ductility and impact resistance but lower tensile strength compared to PVC.
– It is opaque in color and more glossy than PVC.
– ABS also has high corrosion and chemical resistance, which makes it useful for drains.
– It has a lower heat distortion temperature than PVC, around 105°F to 125°F.

The differing chemical makeup of PVC and ABS makes them incompatible for gluing, welding, or transitioning directly. Attempting to join them can result in bonds that are weak and prone to leaking and separation over time.

Can PVC and ABS Be Connected?

While PVC and ABS plumbing pipes cannot be connected directly, it is possible to transition between them with the use of proper adapters and joining techniques. The key requirements are:

– Use appropriate transition fittings. You need an adapter made for connecting PVC and ABS, such as a transition union. Regular PVC or ABS fittings alone will not create a viable connection between the two.

– Prepare the pipes properly. The ABS and PVC pipe ends must be undamaged, free of debris and cleaned with primer/cleaner before applying glue. Match the sizes of the pipes to the correct fitting size.

– Use the right cement/solvent glue. You need a two-part cement formulation made for bonding ABS and PVC together, applied thoroughly to both pieces. Do not use regular PVC or ABS cement alone.

– Allow time to cure fully. The specialized PVC-ABS glue takes longer to cure completely than regular ABS or PVC cement. The connection should not be under pressure and needs undisturbed curing time.

Following these important steps will allow you to transition safely from a PVC system to an ABS drain line or vice versa with the proper adapter. However, there are also cases where avoiding PVC-ABS connections is recommended.

Limitations of Connecting PVC and ABS

While connecting PVC to ABS with a transition fitting is possible, there are some drawbacks and instances where it should be avoided:

– The mixed connection is always the weak point. Even with proper gluing, the bond between PVC and ABS has less strength than pure PVC-PVC or ABS-ABS joints. The transition coupling is more vulnerable to separation and leaking.

– It is not approved for pressurized systems. PVC-ABS connections should only be used for low-pressure drain, waste and vent lines. They are not authorized for pressurized water distribution lines up to drinking water standards.

– Transition fittings have size limitations. PVC-ABS adapters are made in smaller diameter sizes, usually up to 3-inch for residential use. Larger commercial sizes may not be available.

– Code approval is limited. Because of their vulnerabilities, PVC-ABS couplings are restricted by plumbing codes. Their use must conform to code specifications.

– Incompatible temperatures. Since PVC and ABS have different heat tolerances, the mixed joint can fail earlier if temperatures exceed ABS limits.

Following code requirements and the manufacturer’s instructions for PVC-ABS connections is essential to avoid potential failures. In some situations, it is better to cut out the incompatible section and replace it with uniform pipes and fittings rather than making a transition connection.

Where Can PVC-ABS Connections Be Used?

The main accepted uses for PVC-ABS transition fittings are:

– Drainage to sewer conversion. A PVC-ABS adapter can connect a PVC drain system to an ABS sewer lateral line or main sewer line where needed.

– Joining dissimilar drain and vent pipes. PVC and ABS drains and vents can be adapted where they intersect or connect within a drainage system.

– Drain and vent connections to PVC water pipes. An ABS drain, vent, or trap arm can tie into a PVC hot or cold water line with a proper transition fitting.

– Underground drainage transitions. PVC to ABS adapters may be used to connect buried drain pipes to each other where needed.

Even for approved applications, PVC-ABS connections should only be made where necessary. Use them sparingly and only where allowed by code. Avoid them for pressurized water lines, and do not transition back and forth repeatedly.

Examples of PVC-ABS Transition Fittings

PVC-ABS Union

A union fitting allows easy connecting and disconnecting of two pipes. PVC-ABS transition unions have PVC and ABS ends sized for the respective pipes to join. They come apart in two pieces so pipes can be separated later if needed.

PVC-ABS Coupling

Coupling fittings are used to permanently connect two pipes in a straight run. A PVC-ABS coupling has a PVC end and an ABS end sized to fit the pipes. Couplings do not come apart like unions.

PVC-ABS Adapter Bushing

A bushing is used to connect pipes of two different sizes together. A PVC-ABS bushing adapter allows connecting a larger PVC pipe to a smaller ABS pipe, or vice versa. Bushings are permanently connected like couplings.

PVC-ABS Fernco Donut

Flexible rubber Fernco couplings slide over the ends of two pipes to create a flexible, watertight gasket seal. Fernco donuts are made with PVC and ABS ends to transition between the pipe materials.

Transition Fitting	Image	Description
PVC-ABS Union		Two-piece fitting that allows disconnecting PVC and ABS pipes from each other
PVC-ABS Coupling		Single fitting that permanently connects PVC and ABS pipes in a straight run
PVC-ABS Adapter Bushing		Allows connecting a larger PVC pipe to a smaller ABS pipe, or vice versa
PVC-ABS Fernco Donut		Rubber sleeve coupling that seals over PVC and ABS pipe ends

Step-By-Step Instructions for Connecting PVC to ABS

Follow these key steps to ensure proper installation when using PVC-ABS transition fittings:

1. Gather Materials

– PVC and ABS pipes – cut and deburred ends square and smooth
– Approved PVC-ABS transition fitting for pipe sizes
– PVC-ABS solvent cement glue formulated for both materials
– Clean rags, paper towels
– PVC and ABS primer/cleaner
– Safety gear – gloves, goggles, respirator

2. Prep the Pipes

– Ensure pipe ends are cut square with no burrs or degradation
– Wipe dirt, oil and moisture from the outside of each pipe end
– Lightly sand pipe ends if needed to expose fresh material

3. Prep the Fitting

– Check the fitting is suitable for the pipe sizes and materials
– Inspect fitting interior and ends for debris, damage or defects
– For two-piece unions, test dry fit without glue and confirm proper mating

4. Apply Primer and Cleaner

– Use PVC primer on the PVC pipe end only
– Use ABS cleaner on the ABS pipe end only
– Avoid mixing primers; let dry completely

5. Cement the Joint

– Shake or stir the PVC-ABS cement before using
– Apply generous layer of cement to the inside of the fitting
– Apply thin coat of cement to outside of each pipe end
– While cement is still wet, insert pipe ends fully into fitting
– Hold in place for 30 seconds; wipe excess cement

6. Allow Proper Cure Time

– Support joint so it remains aligned while cement cures
– Do not disturb, pressure test or backfill joint for full cure time
– Cure times range from 2 hours to 2 days depending on pipe size

Following this procedure carefully creates a successful transition connection between PVC and ABS piping that should have a long service life if used in approved applications. Always refer to the transition fitting manufacturer’s instructions for proper installation and curing procedures.

Solvent Cements for Joining PVC and ABS

Using the right cement solvent glue formulated specifically for bonding PVC and ABS is critical for proper fusion and sealing of the transition joint. The solvent literally melts and fuses the pipe and fitting materials together to create a permanent connection. Standard PVC or ABS only cements will NOT work for joining PVC and ABS reliably.

Some leading options for PVC-ABS transition solvent cements include:

Oatey All-Purpose ABS-PVC Cement

Oatey Hercules branded all-purpose cement joins ABS, PVC, or ABS to PVC. It softens and destroys the pipe surface materials to achieve fusion bonding. This cement meets ASTM standards D2235 and F628 and compliance codes.

Christy’s Red Hot Blue Glue

This ABS to PVC glue from Christy’s bonds and seals both plastic types with its solvent formula. It remains flexible to absorb vibration and avoids cracking. The glue cures blue for an easy visual cue of full bonding.

Weld-On 717 PVC and CPVC to ABS Transition Cement

Another leading brand for PVC-ABS connections is Weld-On 717, which chemically fuses and hardens the joint. It works on all schedules and classes of solid or cellular PVC and CPVC to ABS.

Oatey All-Purpose Cement in Twist N’ Seal packaging

Oatey also offers its trusted all-purpose ABS-PVC cement blend in a Twist N’ Seal applicator package. This allows controlled application directly into joints and fittings without pouring from a can.

When making the critical link between PVC and ABS pipes, be sure to use only a cement designated for chemically bonding the two specific plastic materials together. Follow instructions precisely for successful connections.

Troubleshooting Common PVC-ABS Connection Problems

While PVC-ABS connections can be reliable when installed properly, there are some common issues that can occur:

Loose Fit in Fitting

– Pipe ends not fully inserted into fitting or improper pipe size for fitting
– Worn-out fitting interior that doesn’t grip pipe end
– Fix by cutting pipe flush and replacing unfit fitting

Leaking at Pipe-Fitting Joint

– Insufficient cement applied to joint and pipes
– Cement not worked fully around joint
– Pipe inserted before cement cured
– Fix by thoroughly re-cementing joint

Cracked or Damaged Fitting

– Fitting hit or stressed while cement cured
– Freezing temperatures during cure time
– Age deterioration of fitting material
– Replace cracked or degraded fitting

Slow or Poor Cement Cure

– Expired cement or improper PVC-ABS formulation
– Low temperature slowed chemical reaction
– High humidity prevented drying
– Obtain fresh cement and ensure proper dry conditions

Diagnosing the cause of connection failures and following manufacturer’s directions can resolve many PVC-ABS joining issues. But if problems persist, replacement may be needed.

Alternatives to Connecting PVC and ABS Pipes

While PVC-ABS transition fittings provide one option for combining the two plastic pipe types, here are other potential alternatives in some situations:

Use All PVC or ABS System

Selecting one pipe material for the entire plumbing system avoids mixed joints. Plan drainage layouts to keep ABS only in lower drainage.

PVC or ABS Coupling Same Size Pipes

Cut out a section of one pipe and replace with the other using couplings. This may lose some length but avoids transitions.

PVC or ABS Socket Adapters to Join Different Sizes

A socket adapter allows joining a larger pipe to a smaller one or vice versa without mixing materials.

Transition to Non-Plastic DWV Pipe Sections

Connect to short sections of galvanized steel or cast iron drain pipe instead of directly between PVC and ABS.

Flexible Coupler Connections

Use rubber sleeve couplings like Fernco instead of rigidtransition fittings in some non-pressure applications.

Considering alternative connection options can provide ways to avoid the potential drawbacks of direct PVC-ABS joining in some plumbing systems and applications.

Conclusion

While PVC and ABS pipes have incompatible properties that prevent reliable direct connections, transitioning between them is possible in drain, waste and vent systems using proper fittings and solvent cement. PVC-ABS connections should only be made where code approved and not used in pressurized water lines. Following manufacturer instructions for preparation, glueing and curing results in durable mixed joints. With the right materials and careful installation, PVC and ABS pipes can be adapted in order to utilize the benefits of both plastic piping types where needed.