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Remove the flange from the dry fit. Ensure the rubber gasket is properly seated on the flange. Insert the flange back into the cast iron pipe, pressing it down firmly until it rests on the floor. Use a wrench or socket set to begin tightening the compression bolts on top of the flange. Alternate between the bolts, tightening each one a little at a time, similar to tightening lug nuts on a wheel. This ensures the rubber gasket expands evenly against the inside of the cast iron pipe, creating a strong, watertight seal. Tighten until snug and the flange feels secure. Do not overtighten.

You're viewing a step from: How to Replace a Cast Iron Toilet Flange with PVC

Intermediate

30 minutes

2/4 Inventory

This project involves the complete removal of an old, likely broken or leaking, cast iron toilet flange and replacing it with a modern, more durable PVC compression-style flange. The process includes removing the toilet, demolishing the old flange, cleaning the cast iron drain pipe, and installing the new flange before reinstalling the toilet and testing for leaks. This guide assumes the cast iron drain pipe itself is in good condition and the work is being performed on a solid wood subfloor from above.

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Frequently Asked Questions

How difficult is replacing a cast iron toilet flange with PVC, and how long should I expect it to take?

This project is rated as intermediate. While it doesn't require specialized plumbing skills, removing the old cast iron and lead/oakum seal can be physically demanding and time-consuming. Expect it to take anywhere from half a day to a full day, especially if you encounter unexpected issues like a stubborn old flange.

What specialized tools are absolutely essential for removing the old cast iron flange and its lead/oakum seal?

Beyond basic household tools, you'll definitely need a cold chisel and a hammer for breaking up the old cast iron and carefully removing the lead/oakum seal. A shop vacuum is also crucial for quickly cleaning up debris and ensuring the cast iron pipe is spotless before installing the new flange.

What are the most important safety precautions I should take when demolishing the old cast iron flange and seal?

Always wear heavy-duty safety glasses to protect against flying fragments and a respirator (like the Honeywell R95) to avoid inhaling dust and potential lead particles from the old seal. Heavy-duty gloves are also essential to protect your hands from sharp edges and the demolition tools.

What's a common mistake when installing the new PVC compression flange, and how can I avoid it?

A common mistake is not thoroughly cleaning and deburring the inside of the cast iron pipe after removing the old flange. Any rough edges, rust, or debris can compromise the compression seal of the new PVC flange, leading to leaks. Ensure the pipe's interior is smooth and completely clean for a watertight fit.