Seamlessly Connecting PVC And Cast Iron (Tips For A Watertight Joint)

Iron hubs are very common in older buildings. If you’re in the midst of a plumbing renovation in such a building, there are scenarios where you may be forced to connect PVC to a cast iron hub.

Because these two materials are very different, you may be wondering if it’s possible to create a seamless transition from PVC to cast iron hub.

Though incompatible, there is a way you can connect PVC to a cast iron hub and that’s what I’ll be discussing in the article below.

PVC Pipe

How to Connect PVC to Cast Iron Hub?

There are plenty of methods out there but the one I’ll be sharing with you entails the use of a no-hub coupling and an iron pipe hub adapter also known as a rubber gasket. These two objects will create a watertight seal with no room for leaks.

Let’s dive straight into how to connect PVC to a cast iron hub;

Step 1: Gather essential materials

You don’t need a lot of tools to pull off this job. At your nearby hardware store, look for a no-hub coupling and an iron hub adapter.

Make sure that you measure the diameter of the iron hub and PVC pipe so that you get them in the exact size. A torque wrench, wire brush, hacksaw, grinder, and screwdriver will also come in handy.

Step 2: Clean the cast iron hub before connecting it to the PVC

If the cast iron hub is in an old building, chances are it’s pretty dirty. Using a wire brush and some soapy water, scrub the dirt inside and around your cast iron hub. This will also remove any rust or scale that may’ve developed around the iron hub.

Step 3: Bevel the edges of the PVC and cut it to the desired length

Even though it’s possible to fit the PVC pipe into a cast iron hub using force, beveling the PVC guarantees a snug fit. Take the electric grinder and create a slope around the edges of the PVC pipe.

Once you’re done, cut the beveled PVC pipe to your desired length. A hacksaw should get that job done. Or, you could use a pipe cutter.

Step 4: Fit the hub adapter into the cat iron hub

The hub adapter or rubber gasket is the one that usually comes first before the no-hub coupling. Slide it inside the cat iron hub and make sure it’s secured firmly.

Step 5: Proceed to fit the PVC pipe into the cast iron hub

Using the side of the beveled PVC pipe, slide it inside the opening of the cast iron hub so that it fits inside the hub adapter.

I recommend using lubricant around the edges of the PVC as it makes penetration easier. Please note that lubricant won’t act as a sealant. This is why you need a no-hub coupling.

Step 6: Install the No-Hub Coupling

It’s now time for the no-hub coupling. Slide it down the PVC pipe until it reaches the transition area. Make sure that it covers both the PVC pipe, hub adapter and the cast iron hub.

On the side of your no-hub coupling, tighten the screws with a screwdriver. Ensure the tightness of these screws is per the instructions provided by the manufacturer. A torque wrench will help you get the required tightness.

And there you have it. You will have perfectly connected the PVC to the cast iron hub. Take a step back and examine if the transition is flawless.

In case you spot some misalignment, unscrew it and put it back together. The last step is to perform a leak test and if everything checks out, you can continue with other aspects of your plumbing renovation.

Cast Iron Hub Fittings

Can You Use Glue to Stick PVC to Cast Iron Hub?

You should never use glue to connect PVC to a cast iron hub. Glue or adhesive may seem like the easiest choice. However, it will not create a perfect bond between these two materials.

PVC glue is designed to connect PVC pipes. Therefore, if you use it with a cast iron hub, the bond won’t last long. Also, such a connection is more vulnerable to leaks.

If you want a secure connection between PVC to cast iron hub, use a no-hub coupling and an iron hub adapter.

Cast Iron pipes

What Can Go Wrong When Connecting PVC to Cast Iron Hub?

As long as you follow the steps I’ve shared with you above, you won’t run into any problems. However, it’s advisable to familiarize yourself with some of the things that might go wrong. This can help you avoid certain mistakes that might lead to issues later on.

So, here’s what may go wrong when connecting PVC to a cast iron hub;

• Incorrect fitment: Before even getting started with this project, you must make sure that the cast iron hub, PVC pipe, no-hub coupling, and hub adapter are of the same diameter. If you get one size wrong, you’ll run into fitment issues. Always confirm the size of your tools.

• Wrong tightening: If you under-tighten the no-hub coupling, the connection won’t be secure and it will leak. On the other hand, if you over-tighten the no-hub coupling, you risk interfering with its structural integrity.

You have to make sure that the connection is according to the measurements of the no-hub coupling manufacturer.

• Failing to lubricate the PVC pipe: Even though it’s not mandatory, lack of lubrication can make it challenging to slide the PVC pipe into the cast iron hub. Also, without lubrication, you may have to use a lot of force which could damage the PVC pipe.

• Misalignment: Sometimes, your connection may be misaligned and that could lead to leaks. To prevent such, always double-check every step before proceeding to the next.

• Damage to the cast iron hub or PVC pipe: During installation, the use of excessive force can damage either the PVC pipe or the cast iron hub, thus leading to costly repairs or replacements.

How to Ensure the Longevity of a PVC to Cast Iron Hub Connection?

There are a few things you can do to ensure your PVC to cast iron hub connection serves you longer, which include;

• Use high-quality materials: From the no-hub coupling to the rubber gasket, you should stick to only high-quality materials. Unlike inferior materials, high-quality coupling clamps last longer and are more resistant to issues like leaks.

• Follow the proper installation method: To ensure your connection lasts longer, make sure that you follow the expert tips shared above. Do not skip any steps because that might affect the reliability of your PVC to cast iron hub connection.

• Make time to inspect the connection frequently: Regular inspection allows you to spot and resolve problems before they become more complex. And by inspection, I don’t just mean checking for leaks.

You should also check for signs of deterioration or damage. it’s through regular inspections that you can spot misalignment. When inspecting the PVC to cast iron hub connection, confirm the tightness of the no-hub coupling.

• Support the entire piping system: Even though this doesn’t relate to the connection between PVC to cast iron hub, supporting the entire system minimizes stress which can affect the structural integrity of the system.

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