Replacing a toilet sounds harder than it is. Most homeowners can pull the old toilet and set the new one in under an hour, until a complication appears. The most common complication is the closet flange, the metal or plastic ring that anchors the toilet to the floor. Years of water and stress leave it rusted, snapped, or shattered, and a new toilet often needs a ring in better shape than the old one can offer. When the bathroom sits on a concrete slab, as basement baths and slab-foundation homes often do, the flange work changes character: the old ring has to be cut free and new anchor holes drilled into concrete.
The job runs about 75 minutes of working time with one to two hours total, at a parts cost of $5 to $15. Skill level sits above average: you need a hammer drill and an oscillating multi-tool, plus enough plumbing sense to set the ring at the right height. Homeowners rearranging the bathroom at the same time can place modular closet systems so the new storage never blocks access to the flange.
Before You Begin: Tools and Safety
Two specialty tools carry the job: an oscillating multi-tool with a carbide-edged blade to cut the old ring free, and a hammer drill with a masonry bit to open anchor holes in the slab. Round out the kit with a chisel, a shop vacuum, a level, and a screwdriver. The tool budget stays near zero if you already own the drill, and a basic multi-tool rents for $30 to $50 at most home centers.
Safety comes first because concrete work makes dust and noise. Shut off the water and flush the toilet to drain the tank before you lift it. Wear safety glasses, a dust mask rated for silica, and ear protection for the hammer drill. Vacuum the debris as you go rather than sweeping it, since dry concrete dust spreads through the room fast. Pick the replacement toilet before the old flange comes out, and what to know before installing a dual-flush toilet covers the bowl size and supply decisions that shape the layout.
Gathering the specialty tools
- Oscillating multi-tool with a carbide blade
- Hammer drill with a 3/16-inch masonry bit
- Chisel and hammer
- Shop vacuum with a dust bag
- Level, tape measure, and marker
- Safety glasses, dust mask, and ear protection
Safety precautions
Confirm the water is off before removing the supply line, and cap the open pipe so nothing drops into the drain. Work in short bursts with the multi-tool so the blade does not overheat, and let the vacuum run continuously near the cutting line.
When to call a professional
This is not the project for a first-time DIYer. If the flange sits flush with the floor or below it, if the drain pipe is cracked, or if the slab has spalled around the old ring, a licensed plumber is the cheaper path. A mistake here means a toilet that rocks, leaks, or damages the subfloor, and the repair bill far exceeds the $150 to $300 a pro charges for the flange work.
Understanding Flange Types and Sizes
The replacement ring comes in two materials. Plastic rings in PVC or ABS resist corrosion, cost $8 to $15, and suit almost every residential drain. Metal rings in brass or coated steel survive heavier traffic and repeated servicing, but they corrode in wet bathrooms and cost two to three times as much. Most concrete-slab replacements use plastic because the ring never carries structural load, only the toilet weight.
Size matches the drain: a 3-inch flange fits 3-inch waste pipe, and a 4-inch flange fits 4-inch pipe, with a 3-by-4 adapter handling the transition. Height matters more than material. The top of the flange should sit about 1/4 inch above the finished floor so the wax ring compresses into a leak-free seal. The toilet choice influences the layout, and choosing the best one-piece toilet for the water closet settles clearance questions before the flange is set.
Metal versus plastic rings
Plastic wins on corrosion and cost, and modern PVC rings hold the toilet bolts as firmly as metal. Metal rings fit situations where the flange gets disassembled often, like rental units, but check the coating for damage before installing, since a scratch turns into a rust line within a season.
Ring height and offset
The 1/4-inch height rule assumes the finished floor is already in place. If the floor is being retiled, set the flange after the tile goes down, not before, or the height lands wrong. Offset flanges shift the toilet 2 inches in one direction to clear a wall or a drain that sits off-center.
| Flange type | Material | Best use | Typical cost |
|---|---|---|---|
| Standard replacement ring | PVC or ABS | Concrete slab, residential | $8 to $15 |
| Repair ring | PVC or ABS | Intact hub, cracked top ring | $10 to $20 |
| Metal ring | Brass or coated steel | Frequent servicing | $20 to $30 |
| Offset ring | PVC or ABS | Drain off-center | $15 to $25 |
Removing the Old Flange
Start with the toilet lifted off and the old wax ring scraped away. Inspect the flange: if the ring is intact and the bolt slots are sound, reuse it, but a cracked or corroded ring comes out. An oscillating multi-tool cuts the ring into two or three segments, and a chisel pops each segment free of the pipe hub. Cut in short strokes, keep the blade against the ring rather than the pipe, and let the vacuum capture the debris.
With the ring gone, clean the hub and the slab. Vacuum the bolt holes and chisel residue, then check the pipe: a PVC hub with cracks or chips needs a plumber before anything else goes in. Concrete that spalled around the old anchors gets patched with a masonry repair compound and left to cure overnight. Once the surface is clean and dry, the new ring sets in minutes. The toilet itself reconnects with a standard sequence, and how to fit a close-coupled toilet and toilet seat covers the positioning that keeps the base level and the seat aligned.
Cutting the old ring free
Two cuts at opposite points split the ring, then the chisel breaks the remaining bond. On rings glued into the hub, cut the ring flush and use a repair ring that slides inside instead of forcing the old hub.
Cleaning and inspecting the slab
Scrape old wax and caulk with a putty knife, then vacuum the entire area. Run a finger around the pipe hub to feel for cracks, and shine a light down the drain to confirm nothing fell in while you worked.
Installing the New Flange
Position the new ring over the drain with the bolt slots aligned to the room, mark the anchor holes with a pencil through the ring, then set the ring aside. Drill each hole with the hammer drill and the masonry bit, going about 1-1/4 inches deep and stopping before the bit binds. Vacuum the holes, tap in concrete anchors, and set the ring back in place. Drive the anchor screws with a driver set to low torque, since concrete strips out fast when the screw is forced.
Check the ring with a level in both directions. High spots come from debris under the ring, so lift, clean, and reset rather than forcing the screws. The top of the ring should sit 1/4 inch above the finished floor, and shims under the ring correct a low side before the anchors are torqued down. With the ring secured, the rest of the toilet internals deserve the same attention, and knowing how to replace a toilet flapper and stop a running toilet catches the most common post-install failure before it wastes water.
Drilling anchor holes in concrete
Use the hammer function only after the bit has seated, let the drill do the work, and pull the bit out periodically to clear dust. Match the bit to the anchor: a 3/16-inch masonry bit pairs with standard 3/16-inch anchors, and the hole depth follows the anchor’s rated embedment.
Setting the flange height and level
The wax ring compresses about 1/4 inch, so a ring sitting high leaves the toilet rocking and a ring sitting low leaves a gap. Measure the ring height against the floor with a straightedge, and shim or grind until the 1/4-inch target is hit.
Securing with concrete anchors
Drive the screws in a cross pattern, snug then firm, and stop the moment an anchor starts to spin. Two anchors opposite each other carry the load in most cases, with a third and fourth added when the ring flexes.
Reconnecting the Toilet and Testing
Set the wax ring on the flange, or on the toilet horn for rings with a plastic funnel, and lower the bowl straight down so the ring compresses evenly. Bolt the bowl to the flange with the supplied washers and nuts, tighten in a cross pattern, and rock the bowl gently to confirm it does not move. Connect the supply line, open the valve slowly, and let the tank fill.
Flush several times and watch the base for water. A bead of caulk around the base finishes the install, but leave the back edge open so a future leak shows up instead of hiding under the seal. If the layout allows options, how to choose the right toilet flange for a plumbing installation covers offset rings and repair rings in more depth for the next bathroom.
Setting the wax ring and seating the bowl
Wax rings cost $5 to $10 and come in standard and extra-thick versions. Use extra-thick when the flange sits below the 1/4-inch target, and never double-stack rings, which squeeze out under the bowl weight and fail.
Flush testing and leak checks
Check the tank-to-bowl gasket, the supply nut, and the base after the first flush, then again after 24 hours. A running toilet after install usually traces to the fill valve or flapper seat, both quick fixes once the bowl is down.
A flange replaced on concrete, with the ring level and the anchors snug, outlasts the toilet it supports. The same attention to detail carries into the rest of the room, and selecting and installing toilet paper holders for home renovations finishes the bathroom so the repair reads as a refresh rather than a patch.