Install Toilet on Concrete With No Closet Flange

What do you do if you remove an old toilet and discover that the closet bolts are rusted out, there is no closet flange, and the waste line is made of terra cotta? You could pay someone $$$$$ to jack hammer out half of your basement floor and connect up to the terra cotta. You could tapcon the toilet bowl to the floor with a rope of plumber's putty like they did in the old days. OR you can do what I did . . .

DISCLAIMER: I am not a licensed plumber. I am not responsible if you injure yourself, cause damage to your property, or violate your local plumbing code.

Step 1: The Problem(s)

Those brown spots above and below the drain pipe are the rusted remains of the closet bolts. I hacksawed the nubs so they were flush with the floor.

The mouth of the terra cotta (or clay) drain pipe is about 7" in diameter. The holes to mount a typical flange line up with the lip of the clay pipe and it wouldn't hold the flange.

Step 2: Break Out the Terra Cotta

The top section of the clay pipe had to go. I chipped it out down to the lower lip (about 1" - 1 3/4" down) using a cold chisel and a hammer.

You can see that I laid ceramic tile in the interim, so I was careful not to chip that.

Also, I covered the lower portion of the drain pipe with duct tape so none of the clay fragments went into the sanitary sewer.

Take your time and chip out a little at a time.

Step 3: Top Part of Drain Pipe Removed

The upper portion of the clay drain pipe is gone. Don't forget to wear safety glasses when forcefully chipping out sharp pieces of clay!

Step 4: Cut ABS Pipe to Length

The lower section is about 4 5/8" in diameter - perfect for accepting a piece of 4" ABS drain pipe. I used the yardstick to mark floor level.

Step 5: Pipe Cut and Fit

The ABS was cut with a mitre saw and dry fit into place. The towel keeps sewer gases from coming into the house.

Step 6: Dry Fit Flange

I dry fit the flange with and without the last ceramic tile.

Step 7: Cement It In

Making sure the ABS was plumb, I cemented it into place with mortar mix.

Step 8: Lay Final Tile

Since I would eventually be drilling into the new cement, I let it cure for a week before laying the final cermic tile with thinset.

Before laying the tile, I used a tile bit to drill holes where the flange would be screwed in. You can see where I cracked the edge of the tile when drilling. :-( No matter. It will be hidden under the toilet bowl!

Again, note the grungy towel stuffed into the hole the keep sewer gases from coming into the house.

Step 9: Install the Flange

I grouted the tile, then . . . the moment of truth:

Using the Tapcon drill bit, I drilled four holes down into the concrete to line up with the holes on the flange. I vacuumed out the holes to get rid of the resulting concrete dust.

I applied ABS cement to the inside of the cemented ABS piece and to the outside of the flange. Then I slid the flange into place and screwed in the Tapcons. I used the kind with the tapered wood screw type head so that once all the way in, they seated nicely in the recessed holes in the flange and held it tight.

Step 10: RESULTS!

Once the flange was in, I let the ABS cement dry for a couple of hours. Then proceeded with a normal toilet installation.

Good luck!



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    13 Discussions


    3 years ago on Introduction

    Has anyone heard of this Culwell Flange? Researching replacing my old flange led me here- was wondering of anyone had heard of it. Seems to be a clever solution to the problem of leakages from under the flange. is their site, I was hoping to get more info about it...


    6 years ago on Introduction

    why all the trouble ?
    if that is concrete under it like mine, after the bolts rusted out ,i just used my rechargeable hammer drill from Home Depot (50 bucks) and concrete bit ,for drilling out the old rusted bolts and on into the concrete ,the further you drill the longer the bolt you need, use two 1/4 inch concrete bolts (Blue) with toilet washers and was of 30 minutes.(the bit has to be slightly smaller then the bolts)
    they won't rust for another 40 years.
    your job looks fine, i just figured my way was a bit easier and also lots quicker.

    I have used that too and will agree that it works very well. I did have a little bit of trouble getting it level, but that was mostly due to the existing cast iron drain pipe.

    Still an excellent instructable.


    8 years ago on Introduction

    I have to do this and I'm not looking forward to it. Thanks for the tips!


    9 years ago on Introduction

    there is all so a nohub toilet fitting that goes over the pipe for this kind of thing.


    10 years ago on Step 9

    Neat work on tile and flange, and the good taste to replace the red tile.


    12 years ago

    Nice fix for a vexing, and hopefully rare problem. Sure beats digging up the slab and starting over! ;-) I wouldn't mind seeing a little more detail in how to do things, (e.g., "what's Thinset") [mortar, I presume] for those not in the know. On the other hand, if they're not, maybe they should stay that way in this case, thereby saving their marriage and a desperate Sunday afternoon call to Fly by Night Exhorbitant Plumbing Co. Any advice on how not to crack the tile when drilling? After all that hard work, it's a letdown to have the finish part go wrong in the end, yes? That would be a great tip, esp. for those that rarely drill the harder stuff.

    2 replies
    Dun MalgMarcos

    Reply 12 years ago

    To avoid cracking tile: 1) use a sharp carbide tipped masonry bit and squirt water on it periodically as you drill 2) drill slowly to minimize heat and vibration 3) use less and less pressure the deeper you get, till you're almost not pressing at all when you break through the back of the tile


    Reply 12 years ago

    Thanks for your comments. Laying tile was incidental to the project, and I am by no means an expert, so I skimmed over that part. Cracking a small corner of the tile was no big deal. I filled in the gap with thinset mortar and that part is hidden under the toilet anyway. I'm sure there are great instructables out there for laying tile and doing the final toilet installation for that matter.


    12 years ago

    Your pics are very helpful . Thanks !


    12 years ago

    Nicely done. I've run into a similar problem with a slab foundation and terribly rotted closet flange (metal) attached to PVC pipe. Unfortunately, PVC cement is permanent, and I ended up cutting a sizable chunk of the old pipe down with a Dremel tool (only thing I could use to cut below floor level!) and then retro-fitting a piece of PVC to use as a flange attachment. What a pain that job was! Nice fix.

    Tool Using Animal

    12 years ago

    no comment on the plumbing, but thanks for showing the right way to tile, can't believe how many times I've seen people lay tile around a toilet and just cut the tile to fit around it, ugh !