How To Install a New Toilet Flange on a Concrete Slab

Toilet room in the modern interior
Artem Ermilov / Getty Images
Project Overview
  • Working Time: 1 hr, 15 mins
  • Total Time: 1 - 2 hrs
  • Skill Level: Advanced
  • Estimated Cost: $5 to $15

Replacing a toilet is one of those bathroom projects that sounds difficult but actually isn't. Even beginner DIY plumbers find that they can remove the old toilet and put in the new toilet in less than an hour, as long as there are no complications.

One complication that frequently arises has to do with the toilet closet flange—the metal or plastic ring that attaches the toilet to the floor.

When replacing a toilet, it's fairly common to discover that the existing toilet flange will not work for the new toilet. Subjected to water and stress for years, it might be rusted, snapped in half, shattered, or just too gunked up to be reused.

You may have a concrete subfloor, as is often the case with basement bathrooms or other slab foundation situations. Removing and replacing the toilet flange in concrete is no easy matter. It can be quite hard to drill holes to screw down a toilet flange in concrete to secure the new flange. Fortunately, a couple of tools will help with the process.


Fixing a broken toilet flange or replacing a toilet flange on concrete or tile can be very difficult and is not a project for the average DIYer. Only those with an above average understanding of plumbing and experience working with power tools should attempt this project.

Before You Begin

Using two specialty tools—a multi-tool or similar cutting device, along with a hammer drill—makes it easier to install a toilet flange on concrete.

Unlike conventional drills that just rotate the bit, hammer drills rotate and also move the bit up and down ever so slightly, which creates a pounding action along with the drilling motion. You can find an inexpensive hammer drill at a home improvement store or tool rental outlet. If your usage will be only occasionally, renting a hammer drill is probably your best option. If you expect to drill into masonry more often, purchase a good-quality tool.

Because the old bolts will need to be cut off, you'll need some type of power tool to do the job. A manual hacksaw will not work, because you need to move the saw blade against and parallel to the concrete slab. Either an oscillating multi-tool equipped with a metal-cutting blade or an angle grinder will do the trick.

Safety Considerations

Once the toilet has been removed, plug up the open pipe with old rags to prevent sewer gasses from escaping. This also helps if you accidentally drop a tool down the pipe. Work with latex gloves and thoroughly wash up after replacing the flange.

What You'll Need

Equipment / Tools

  • Hammer drill with 1/4-inch masonry bit
  • Multi-tool or angle grinder
  • Putty knife
  • Tape measure
  • Screwdriver


  • Toilet (closet) flange
  • Latex gloves
  • Trash bag
  • Tapcon screws


How To Install a New Toilet Flange on a Concrete Slab

  1. Cut off the Old Flange and Obstructions

    After you remove the toilet, you will probably find an existing toilet flange. (It is very rare to find a toilet that is attached to the sewer line without a flange.) You will need to remove this old flange and any obstructions before you can install the new flange.

    On concrete slabs, the old flange will be attached via bolts embedded in the concrete. If the old bolts are in good condition and match up perfectly with the new flange, you can keep them in place to secure the new flange. But if the bolts are unacceptable (too rusted, mismatched, too short, etc.), they must be cut off before installing the new flange.

    Use an angle grinder or a multi-tool equipped with a metal-cutting blade to hack off the bolts and other protruding obstructions. Make sure that all of these pieces are cut down perfectly flush with the concrete.

    Saw using to cut off the old toilet flange and bolts.
    Lee Wallender
  2. Scrape off Old Wax Ring

    After you remove the obstructions, the old wax ring will still be in place around the drain opening. The wax most likely will be thick, sticky, and possibly stained with sewage. Removing the wax ring requires patience, a putty knife, and latex gloves. Methodically remove all traces of the old wax ring and deposit the bits directly in a plastic bag for disposal.

    The old wax ring must be scraped off of the concrete floor.
    Lee Wallender
  3. Pick the Correct New Toilet Flange

    Take careful note of the size of the newly exposed drain pipe: Your new flange needs to match this pipe. Measure the diameter to help you purchase the replacement flange, or, if possible, take the original flange with you to the store to serve as a guide.

  4. Place T-Bolts in New Toilet Flange

    Place the T-bolts upside-down in the new toilet flange so that the threaded shafts are sticking up. Having the bolts in place helps you better visualize how the toilet will be positioned.

    Person placing T-bolts on the flange.
    Lee Wallender
  5. Position Toilet Flange

    Press the toilet flange down into the drain opening, using the T-bolts as reference points for positioning. Make sure both bolts are at equal distances from the back wall, which will ensure that the toilet tank will be parallel to the wall. You can rotate the flange in either direction until you have reached the preferred position. After the toilet is placed, you will have the opportunity for some minor rotation, but it is still best to get the position as straight as possible before securing the flange. Make sure the flange fits snugly, with no gaps.

    Person using a tape measure to determine the toilet distance to the back wall.
    Lee Wallender
  6. Drill Holes Into Concrete

    With a hammer drill and 1/4-inch concrete/masonry bit, bore four holes equidistant around the ring directly through the holes in the toilet flange and down into the concrete subfloor. Use the hammer drill's depth gauge to reach the necessary depth so you can bolt into concrete.


    Be careful not to let the drill angle towards the sewer pipe—if you accidentally break the top lip of the sewer pipe, repair or replacement will be costly and difficult.

    Person drilling holes into the concrete with the hammer drill.
    Lee Wallender
  7. Screw Toilet Flange Onto Concrete

    Use Tapcon anchors or a similar type of masonry/concrete screw to fasten the toilet flange to the concrete slab. If using a plastic flange ring, be careful not to crack the ring by screwing the anchors in too far.

    With the toilet flange in place, you are ready to install the toilet with a new wax ring.

    Person screwing the toilet flange onto the concrete floor.
    Lee Wallender

When to Call a Professional

Removing the old toilet flange is a dirty task that can challenge even the most tolerant do-it-yourselfer. Drilling into concrete and placing fasteners are specialty sub-projects that many do-it-yourselfers have never done. In either case, you may want to call a qualified licensed plumber.

  • Can you install a toilet on a concrete floor?

    You can install a toilet on a concrete floor if the drainage pipe and associated plumbing are in place and you are not moving a toilet. If you find that there is nothing there for you to screw the toilet flange onto the concrete floor, you'll have to drill the proper holes using a hammer drill and a 1/4-inch concrete/masonry bit. Drill four holes equal distance from each other into the concrete floor.

  • What size screws are used for a toilet flange in concrete?

    Since the standard size for toilet flange screw holes is 1/4 inch by 2 1/2 inches, you will need masonry screws that are 1/4 inch by 2 1/2 inches.

  • How do I replace a PVC toilet flange in concrete?

    Though toilet flanges can be made from PVC, ABS (another type of strong plastic), copper, cast iron, or even brass (for older homes), you'll likely work with a PVC flange that matches the sewer pipe. You will need to unbolt the existing flange from the concrete to replace it with a new flange.

Watch Now: How to Properly Set a Toilet to Prevent Leaks