How To Replace A Cast Iron Toilet Flange In Concrete
When it comes time to replace a toilet, you might find that the existing toilet flange does not work with the new toilet. When you have concrete flooring, which is the case with slab foundations or basement bathrooms, replacing that flange can be quite difficult.
Finding that you have a cast iron toilet flange presents another set of issues. The good news is that, with an intermediate level of skill, you can fix the problem in about 90 minutes and for under $20. You just need to cut away the old flange, scrape off any ring wax, and install the new flange.
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Cast Iron Flanges
Whether broken or looking to replace it, a cast iron flange can be a pain to properly fix. Most of the time, the cast iron is so thick that going with a split-type repair flange means being too thin to make an impact. The full-sized spanner flanges, on the other hand, are damn near impossible to install because you can’t easily drill into a cast iron flange.
Cast iron is highly durable, so if you are looking for longevity out of your flange, that is the way to go. That said, if you are looking to repair a cast iron flange, you are better off just removing it entirely and installing a new one.
How to Replace a Cast Iron Toilet Flange in Concrete
It is important to note that there are difficulties here, but not in the way that you might think. The good news is that you won’t have to remove much concrete. Cutting out a square just larger than the space the flange occupies should be more than enough to work with.
From there, it is just a matter of following this step-by-step guide to get the job done. For those DIYers out there with a moderate level of skill, you are looking at about an hour and a half. Less experienced DIYers might take longer, but that is okay. This is a learning experience no matter what.
Step 1: Tools for the Job
Before you can begin, you need to come armed for battle. Having the proper tools can make the job a bit smoother. When it comes to working with concrete and cast iron, anyway that you can make this easier will be infinitely beneficial.
You will need a new toilet flange, some Tapcon screws, latex gloves, a trash bag (for cleanup), a multi-tool or angle grinder, a hammer drill with a ¼-inch masonry bit, a tape measurer, a screwdriver, a chisel, and a hammer.
Step 2: Creating a Hole in the Concrete
When you remove the toilet, you may find one of two things. You should either see the flag jutting out of the floor on its own or a square cut out around the flag. If the square has been pre-cut, you can skip to the next step.
Should you need to create an opening in the concrete, you can do so with your chisel and a hammer. Create a square around the flange so that you have a little room to work with. Even something 6” x 6” should be plenty to work with. Try to keep your work as even as possible, too.
If you do this properly, you won’t have to fill it back in since the toilet will sit over top. So use extra caution when breaking apart the concrete.
Step 3: Cutting Out the Old Flange
Remember that with cast iron flanges, you are better off simply replacing rather than repairing. Even if you think your cast iron flange is worth salvaging, scrap it and replace it with a new one. The cost is low enough that you will hardly notice the difference.
Using your angle grinder or multi-tool, coupled with a metal cutting blade, cut the old flange free. When you remove the top piece, the rest should come out easily. Just be careful and make sure that you don’t slip while cutting the flange.
Step 4: The Bolts
On concrete slabs, the old flange should be attached to bolts embedded in the concrete. Note the condition of the bolts. If they match up with the new flange and are in good shape, keep them for the new flange. If they aren’t in good shape, though, cut them off before installing the new one.
This is where your multi-tool or angle grinder will come in handy. Use a metal-cutting blade to cut those bolts out. Make sure that you cut the bolts down so that they are totally flush with the concrete.
Step 5: Scrape the Old Wax Ring Off
When the flange and any obstructions like the bolts are out of the way, you should notice an old wax ring sitting at the opening of the drain. The wax ring is probably sticky, thick, and maybe even stained from sewage.
This is where latex gloves and the putty knife come into play. Coupled with a lot of patience, scrape up the old ring and put the bits right into your plastic bag so that they can be disposed of easily. By far the grossest part of the job.
Step 6: New T-Bolts
If you managed to salvage the bolts from the previous cast iron flange, you can skip ahead. But if you had to cut them away, you will need to install new ones accordingly. After all, the flange needs something to grab hold of.
Place the T-bolts upside-down in your new flange. Make sure that the threads are point up at you. When you have the bolts in place, you can get a better visualization of how the toilet will then be placed.
Step 7: Positioning the Flange
Take your new flange and press it down into the opening of the drain. You can use your new T-bolts as a reference for positioning. Ensure that both bolts sit an equal distance from the wall where the toilet will be positioned. That means the toilet will be parallel to the wall.
Rotate the flange as needed to get the right alignment. Even after the toilet is placed, you will have a chance for some rotation, but it is easier at this point. Not only that, but it will ensure that the flange is straight before securing.
Step 8: Drilling New Holes
You now need the hammer drill and the masonry bit to bore four holes that are equidistant from one another around the ring. They will go through the holes in the toilet flange and right into the concrete subflooring itself.
You can use the hammer drill to gauge depth, just be careful not to angle the drill towards your sewer pipe. If you break that top lip, replacement or repair is super difficult and very costly. So, proceed with caution.
Step 9: Screwing the New Flange in Place
Finally, it is time to screw the new flag into place. Use those Tapcon anchors (or a similar type of concrete/masonry screw) to fasten your new flange into the concrete slab. If you make the switch to a plastic flange, make sure that you don’t overtighten or you could break the flange.
You are now ready to install your new toilet complete with a new wax ring. The process is really not all that bad, even for the most amateur DIYers out there. Just check your work and ensure that the flange is properly secured in place and does not move at all.
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When in Doubt, Call a Professional
All that said, there is no shame in needing professional help. This job requires quite a bit of tools and is better for those with at least a moderate level of DIY experience. Should the task seem daunting, don’t force yourself to do it.
A professional can come out and do the job in short order. Moreover, they are better suited to handle situations that may have been unexpected. Instead of having to guess and hope that you are doing the right thing, you can rest easy knowing the job will be done right. That saves you time and stress while providing peace of mind.
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Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.
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