How to Repair a Cast Iron Toilet Flange

Stop relying on plastic repair flanges and consider these steps for a more solid solution when preparing to fix a cast iron flange

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A broken cast iron toilet flange can be a pain to fix properly. Most times the cast iron flange is so thick that the split-type repair flanges are too thin to make an impact, and the full-sized spanner flanges are near impossible to install because cast iron is not easy to drill into. You need to remove the flange and start from scratch.

Here are some tips to keep in mind.

Pulling the Old Flange

Your first temptation will be to take a cold chisel and break that existing cast iron flange into pieces to make way for a new PVC repair flange. There is an easier way. Stop looking at that flange as if it is immovable. That flange was centered, packed, and poured with molten lead and can be removed in reverse order.

First, take a high-speed drill bit and drill a few holes in the old lead right alongside each other in a row so that you can have a starting point to pull the old lead out. If you can find and order an old “pitching” tool, do so. The pitching tool looks like a chisel that is straight on one side and bowed on the other, almost resembling a butter knife. If you can’t find one, you can either make one or find something similar. Once you get a starting hole in the lead, it’s time to beat that iron knife around and pry the lead up and out of its setting. 

Once you work the lead and pull it out, it is time to pull out the oakum. Oakum is the oiled hemp that was shoved down into the joint before pouring the lead. You will be surprised how tightly packed the oakum is between the flange and the cast iron piping. Once you have both the lead and the oakum removed, pull the cast iron flange up away from its resting place and take a wire brush and do your best to clean the outside of the pipe that remains.

Tools, Setup and Prep

Cast iron flanges come in two measurements. The first measurement is the diameter of the pipe — 3-inch or 4-inch. The second measurement is the depth of the flange — 2, 3, 4 or 6 inches. That’s because they are made to accommodate fluctuating floor levels. Get the one that you want ready and on site. You will need some basic tools to get molten lead. You will need to make a one-time purchase of the following hand tools — an offset yarning iron, a caulking iron with a fairly thick base, and an iron ladle. The materials you need to have handy are lead, oakum, a ball-peen hammer, and a means to melt the lead.

The yarning iron is a long, thin offset tool that is used to push and pack the oakum into the joint. The caulking iron is an offset tool loosely resembling a cold chisel that beats the lead down into the joint after the lead pour hardens. The ladle is used to hold the lead as it becomes liquefied and is used to pour the molten lead into the joint. If you are using a torch to heat the lead, you will only need a ladle. If you are using a Bunsen burner, you will need both a ladle and a melting pot because it is much easier. The Bunsen burner is, in my opinion, far easier since you can turn it on and let it do its thing. It is possible to get the lead too hot. Old-timers would roll up a piece of paper and dip it into the molten lead; if the paper lights on fire, it’s too hot. If the paper doesn’t light on fire, it is ready to go. You will notice the impurities rise to the top of the molten lead. Skim them out with your ladle and discard them.

Yarning the Joint

Set your cast iron flange around the pipe, making sure that it is centered. Now take your oakum and roll it with your hands, then shove it down between the pipe and the flange. You want to pack the oakum in with your yarning iron and ball peen hammer leaving about 1 inch of room for the lead.

Pouring the Joint

Once you have the oakum packed, it’s time to pour the lead. Take a towel and push it inside the pipe in order to prevent lead from going down the drain. Take your molten lead in the ladle and pour the lead into the joint with one continuous pour. You want about 1 inch of lead on most common toilet flange joints. Or pour it until it reaches the top fill.

Caulking the Joint

It is now time to do the most important part — caulking the joint. Take your caulking iron and beat the lead down with your hammer all around. There are all different kinds of caulking irons sold for inside pushes, outside pushes, wide bars, short bars, all of which you will understand once you actually caulk your first joint. The goal here is to “set” the joint. Pound the lead uniformly around the joint, packing the lead down into the oakum and sealing the joint for good. Now you can screw down the flange and set your toilet.

You will be utterly shocked how solid this flange sits, and more than likely you will never use those cheap plastic repair flanges again.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 


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