How to Install a Toilet Flange on a Concrete Slab

Installing a Toilet on a Flange
Before installing a toilet, you first need to install the toilet flange. Creativel/Getty Images
  • 01 of 07

    Toilet Flange Installation Made Easy With a Hammer Drill

    Toilet Flange Resting In Place In Sewer Pipe
    Unattached toilet flange resting in place on concrete floor. Lee Wallender

    Have you removed an old toilet and discovered that the existing toilet flange will not work for your new toilet because you have a concrete slab floor? As you may have already discovered, it is not easy to remove and replace the flange. One reason is that it is difficult to drill holes into concrete.

    Learn how to install a toilet flange on a concrete slab floor by using a multi-tool or other metal cutting device and a hammer drill.

    Tools and Materials

    • Hammer Drill: One tool that makes this project go smoother is a hammer drill. Unlike conventional drills which just rotate, hammer drills both rotate and move the bit up and down, ever so slightly. For concrete and other masonry drilling, hammer drills are about the only way to go. You can purchase or rent an inexpensive hammer drill at one of the ​home improvement stores. As a homeowner infrequently drilling into concrete, renting a hammer drill is probably your best option. If you plan to drill into masonry more often, save yourself the frustration and get a higher quality tool, such as a Bosch, Hilti, DeWalt, or Milwaukee hammer drill.  
    • Multi-Tool or Angle Grinder: Because the old bolts will need to be cut off, you need some type of power tool that will 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.
    • Toilet Closet Flange: Toilet flanges are key elements at connecting toilets to sewers because this is where the wax ring goes. Not only that, they perform the job of securing the toilet to the floor and keeping it stable.
    • Tapcon Screws
    • Putty Knife
    • Latex Gloves
    • Trash Bag
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  • 02 of 07

    Cut off the Old Flange and Obstructions

    Cut Off Old Bolts and Flange
    Cut off the old toilet flange and bolts. Lee Wallender

    After you remove the toilet, most likely the old flange will be in place. It would be very rare to find a toilet that is attached to the sewer line without a flange. You will need to remove the old flange and any obstructions before you can install the new flange.

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

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

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  • 03 of 07

    Scrape off the Old Wax Ring

    Scrape Off Old Wax Ring
    The old wax ring must be scraped off of the concrete floor. Lee Wallender

    After you remove the obstructions, the old wax ring will be in place. The wax most likely will be thick, gunky, and stained with sewage. Removing the wax ring requires patience, a putty knife, and thin latex gloves. Methodically remove all traces of the old wax ring and deposit the bits directly in a plastic bag.

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  • 04 of 07

    Place T-Bolts in Flange

    Place T Bolts In Flange
    The T-bolts should be placed on the flange. Lee Wallender

    Place the T bolts upside-down in the flange so that the threaded parts are sticking up. This step is all about placement of the flange, not about installing the toilet. Having the bolts in place helps you better visualize how the toilet will be positioned.

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  • 05 of 07

    Measure to Ensure That the Toilet Parallel to the Wall

    Measure To Ensure Toilet Parallel To Wall
    It is necessary to measure the toilet distance to the back wall. Lee Wallender

    Press the toilet closet flange down into the sewer pipe. Use the T-bolts as positioning points. You will want both of them to be at equal distances from the back wall. This 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. Even after the toilet is placed, you still have the opportunity for some minor rotation. Even so, it is always best to get the position as straight as possible before placing the toilet.

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  • 06 of 07

    Drill Holes Into Concrete

    Drill Holes Into Concrete
    Drill holes into the concrete with the hammer drill. Lee Wallender

    With your hammer drill and 1/4-inch concrete/masonry bit, bore 4 holes equidistant around the ring directly through the holes. Use your hammer drill's depth gauge to reach the necessary depth. Be careful not to let the drill bear towards the sewer pipe. If you break the top lip of the sewer pipe, repair or replacement will be costly and difficult.

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  • 07 of 07

    Screw the Toilet Flange Onto the Concrete

    Screw Toilet Flange Onto Concrete
    Screw the toilet flange onto the concrete floor. Lee Wallender

    Use Tapcon or similar masonry/concrete screws to fasten the closet flange to the concrete slab. If using a plastic flange ring like the Sioux Push Tite flange, be careful so that you don't crack the ring by drilling in too far.