Replacing a toilet on a concrete floor is one of those DIY projects that is a lot more difficult than it sounds. If you have nothing to screw a toilet flange to a concrete floor, you’re stuck, right?
Fortunately, no. Even if you have no concrete holes to anchor the new flange, there are only two complicated parts of the project: Removing the old flange and drilling new holes for the new flange.
Short Answer: You can affix a new flange to a concrete floor by drilling new bolt holes or using the holes from the old flange. The tricky part is cutting out the old flange, but a reciprocating saw can make the job simpler.
Decide Whether You Need a New Flange
The first step is to assess the concrete floor and whether you need to install a new flange. While flanges are not universal, many fit different toilets. It is possible to use the old flange, and it will function exactly like a new flange.
I suggest you get the following tools to replace your flange:
- Reciprocating saw
- Small chisel
- Hammer drill
- Large old towel
- Medium tip Sharpie
- New wax toilet ring
- Measuring tape
Remove the Old Toilet and Flange
Remove the Old Toilet
I always say it’s best to turn off the water to the toilet and drain it. Unscrew the bolts that hold the toilet to the flange and remove the toilet. Place the toilet on an old towel that’s big enough to cover the entire toilet’s base and then some.
Putting the toilet on a towel does two things:
- Protects your floor from debris, dirt, and excess toilet wax
- Protects the toilet from chipping on the concrete floor
Place a towel into the drainpipe one inch below the end of the flange sleeve to prevent toilet gasses from entering your home and debris from the flange from falling into the drainpipe.
Remove the Flange Screws or Bolts
Once the toilet is secure, remove all of the wax ring from the flange. Inspect the flange once the wax is off and figure out what is wrong (if you are reinstalling the old toilet). Unscrew the bolts that hold the flange to the concrete and attempt to lift the flange off the drainpipe.
I know it may be hard but try and preserve the bolt holes as best you can. You may be able to use them with the new flange if the bolt holes on the new flange match the holes in the concrete. If you cannot get the bolts to budge, you will have to cut them out.
Cutting Out the Flange Bolts
If the bolts do not budge, you need to cut them out. Use an angle grinder or oscillating multi-tool to cut the bolts even with the concrete floor. Be careful not to damage the concrete with the angle grinder or oscillating multi-tool.
Remove the Flange
While the flange sleeve is likely sealed to the inside of the drain pipe, in some cases, the seal will not have been done properly, and the flange will lift out. Sometimes, if the sleeve fits tightly to the drainpipe wall, it will not have been sealed with PVC cement. If the fit is tight, you may need to pry the sleeve out with a pry bar.
Cutting Out the Flange
Is the flange sealed with PVC cement? Then you must cut it out. Use the reciprocating saw and cut off the top of the flange, flush with the floor. Remove the flange top and cut the drainpipe and flange sleeve flush with the floor if needed.
The next step is to separate the flange sleeve from the drainpipe. Holding the reciprocating saw vertically, cut through the sleeve to the drainpipe. Make sure your cut is straight. Do not cut into the pipe itself. Keeping the reciprocating saw steady can be challenging, especially if you have not used one before.
To overcome this, use the old advice about knives: Take your time and let the saw do the work. You want to make six or seven vertical cuts into the flange sleeve.
Once you have made your vertical cuts, use the hammer and chisel and carefully separate each segment of the flange sleeve from the drainpipe. Do not worry if you nick or even chip the edge of the top of the drainpipe.
Installing the New Flange
Before you do anything else, fit the new flange into the drainpipe. Try and line up the holes for the screws or bolts to anchor the flange to the cement floor. If they line up perfectly, you can use the bolts from the old flange to anchor the new one to the floor.
If not, you will have to drill new bolt or screw holes.
Positioning the New Flange
Put your new flange into position on top of the drainpipe, making sure that the anchor holes in the flange do not align with the old anchor holes. To ensure you have it aligned properly for the toilet, insert the toilet bolts into the slots on the flange. Measure the distance of each bolt from the wall and ensure they are even.
Once you have both bolts lined up, use the Sharpie to mark the cement underneath the flange bolt holes. You will use these markers to drill holes for the new bolts.
Drilling the Flange Bolt Holes
Using the hammer drill, fitted with a ¼-inch concrete or masonry drill bit, bore four holes where you made your Sharpie markers. Be careful not to drill towards the drainpipe.
You do not want to drill into the drainpipe. A drill hole would be bad, but that type of jarring pressure could crack the pipe, creating an all-new, much more complex plumbing issue.
Carefully drill down into the concrete subfloor. Use the hammer drill’s depth gauge to ensure you drill deep enough but not too deep.
Fit The Flange and Bolt it To The Floor
When drilling your holes, you need to fit the flange, lining up the flange bolt holes with the holes you drilled into the concrete subfloor. When you have them aligned, screw the flange bolts into the subfloor.
Be careful not to over-tighten the screws or bolts as that can lead to them breaking the flange, and you have to start all over again.
Reinstalling the Toilet
Once affixing the new flange firmly to the floor, fit the new wax ring in the appropriate place on the flange. Do not press it down, but make sure the wax forms a light bond. Position the toilet using the toilet bolts as a guide, lining them up with the holds at the side of the base of the toilet.
Lower the toilet onto the bolts and carefully wiggle the toilet right, left, forward, and backward. Wiggling the toilet will help build a seal between the exit hole in the toilet and the wax ring.
After wiggling the toilet into position, tighten the toilet bolts. Sit on the toilet for a couple of minutes to secure the wax bond.
Once fastening the toilet to the flange, flush it and look for leaks. You are good to go if no water comes from underneath the toilet!
If you have nothing to screw a toilet flange to a concrete floor, there is no need for concern (for help knowing what size bolts you need, read our guide here). I’m not a professional, but I find installing a new flange straightforward. By following these directions and using care and proper precautions, you can ensure your toilet and flange will give you years of service.