How to connect PVC to cast iron

Though not commonly used these days, some homes still feature cast iron pipes in the plumbing system.

As such, it becomes necessary to devise ways to join PVC pipes to existing cast iron, for example, when upgrading drainage pipe installations in your house- which is not an easy task.

Why?

Unlike the friendly PVC piping, PVC is insanely difficult to cut.

Worse still, a cast-iron pipe is quite heavy and can be a pain to control.

That said, connecting PVC to cast iron is not an impossibility and there are several different ways you can make the connection.

We share some insights on tackling this plumbing problem step-by-step below.

How to connect PVC to cast iron

There are a few great PVC-cast iron couplings in the market and these come in very handy.

If you’re to go the connector way, we suggest that you use Fernco’s popular rubber couplings.

Keep reading to learn how to connect PVC to cast iron with Fernco’s special couplings.

How to use Fernco coupling to connect cast iron to PVC

Fernco makes lots of different-sized pipe couplings for this sort of connection and they fit nearly all types of situations.

Besides, their dimensional flexibility guarantees leakproof seals on cast iron and virtually any piping material.

Keep in mind that you must be sure of your pipes’ thickness – both the PVC and cast iron pipe openings- when shopping for a Fernco coupling (Fernco Donut to some folks).

It’s also worth mentioning that only shieldless Fernco couplings are to be used for below ground connections.

Procedure

Stage 1: Cutting the cast iron pipe

There are two ways you can cut out a length of the pipe:

  • with a snap cutter
  • Using your reciprocating saw

We shall concentrate on these two but I must say that cast iron pipe cutters make quick work of the pipe and could be an option (you may rent/borrow).

Cutting the cast iron pipe with a snap cutter

  1. Measure and mark the point you want to cut the pipe using chalk (draw a straight chalk line).
  2. Grab the chain of your snap cutter and wrap it around the pipe. Be sure to have many cutting wheels against the tape when doing this.
  3. You’re now ready to cut- put pressure onto the cutter’s handles such that the wheels begin to cut into the piping. 
  4. Repeat the above steps at every other chalk line as required.

How to use reciprocating saw to cut cast iron pipes

  1. Mount a metal cutting blade (make sure it’s long enough) onto the saw.
  2. Mark the lines to be cut, still with chalk (keep them straight).
  3. Hold your pipe in place (ensure its firm or have a friend help you hold it).
  4. Set the saw at a reasonably low speed and leave the blade to cut the pipe for you. 

Tip: Do not apply excessive pressure onto the saw as it may make the blade snap. Also, oil the blade frequently especially if cutting several pipes.

Stage 2: Making the connection

Having removed a length of the old cast iron pipe, we can move on to joining the PVC pipe.

  1. Unpack the Fernco and slide it on the PVC.
  2. Get hold of the PVC and insert it into its cast iron pipe counterpart to complete the connection. Be careful here to prevent possible leaks (the PVC should be fastened tight into the cast iron).
  3. You can conduct a pressure test before concealing or backfiling if applicable.

Tip: Rubbing some dish soap on the insides of the Fernco couplings will help make them slide more easily onto the pipe.

PS: You can order an appropriately sized Fernco coupling from Amazon.

How to connect PVC to cast iron hub

If you’re looking at connecting PVC to cast iron hub – perhaps a section of your cast iron piping has corroded badly- the ‘donut’ will still be useful.

Follow these steps:

Step 1: Cutting the existing cast iron pipe

First, cut your existing cast iron pipe about an inch (or even two) above the hub.

An effective tool to use for the job– if you don’t want to use the reciprocating saw or the ratcheting snap cutter- is the angle grinder (install an abrasive cut-off disc for this task).

Try hard until the pipe breaks from the hub while being keen not to cause damage.

Step 2: Clear the lead and oakum

You now need to get all the lead and oakum out of the hub/socket. Just use a screwdriver for this procedure.

After you have removed the lead, proceed to clean up the hub.

A wire brush could be practical to use in this case.

Step 3: Mount the Fernco donut and connect the pipe

Fix the Fernco into the hub then fit your new PVC piping.

As seen earlier, applying a little dishwashing solution on the pipe helps lubricate the part and will make it slide easily.

Alternative Method: Make the connection with Lead

Though not as easy as using Fernco special rubber donut, you can use lead to connect PVC into a cast iron hub too.

If done well, the lead works just fine – simply make the right alignment and pour the molten lead in the joint and you’re toast.

We however strongly discourage this not only because it’s more work but also some PVC manufacturers will never approve of lead connections.

Plus, there is a risk of the hot lead could melt your PVC.

Lastly, some building codes only allow the use of rubber accessories to connect PVC pipes to cast iron and you will be courting trouble with this approach.

Conclusion

This article has taught you how to connect PVC to cast iron.

Of course, there could be other DIY methods out there with varying levels of difficulty and it’s upon you to choose the technique that you feel works best for you.

Ultimately, the method with the widest acceptance even among professionals is the use of a Fernco Donut.

We encourage you to prioritize it.

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