Cannot screw toilet flange to concrete floor

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DanFL

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I had a toilet moved for my bathroom renovation (house on concrete slab) and here is the new rough in that the plumber did. That's 3" PVC. He used some Ramboard to make a dam around the pipe when he refilled the concrete, so there is a void around the pipe about 1" from the pipe to the newly poured concrete. (I've never seen a toilet rough in done this way. I've always seen 4" stub out with solid concrete pour all around, but I'm not a plumber so maybe there was good reason for this...)

When I set the flange on the 3" pipe, any way I rotate the flange, the mounting screw holes line up either over the void, or only about 1/4" from the edge of the solid concrete. I'm concerned that it will just chip out as I drill the holes. There is some minor movement of the pipe + flange when I dry fit it, so it seems to me that I need to secure it to the slab. Can I get away without screwing it? I know those mounting holes on the flange are there for a reason, but are there any cases when I can get away without screws?

I was considering a couple options:
1. Attempt to drill and secure as best as possible with the current configuration. I could probably get at least 1, maybe 2 screws in this way if the concrete doesn't chip out.
2. Install a 3" to 4" coupling with 4" PVC stub out, and then fill the the void with concrete or thinset. Then I can cut that flush with the tile and install the flange inside the 4" sitting on top of the tile. This should eliminate any movement of the pipe and I have something solid to screw into. But... there may not be room for that as the hole is only 4" deep. I don't have a couple to confirm if this would fit.

Other suggestions are much appreciated!
 

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Reach4

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I would use a flange with a stainless steel ring. That is thinner. Then I would top that with a repair ring that has mounting tabs. Align the slots before screwing down the repair ring. There may be a better way, but I am sure this would be strong.

PASCO 21013 and Superior 21015 are repair rings with mounting tabs outside.
red_ring_repair_1.jpg


Another possibility would be to put a spacer reserving enough for your outside closet flange, and fill the rest with mortar. Then screw your flange into the mortar+concrete.
4 in. x 82 ft. R-2 Foam Closet Wrap is intended for the spacer purpose.
pipe-insulation-38712-64_145.jpg

You could dig out the foam after the mortar sets, but I think you may be able to melt it out with a torch. They make a cylinder to go over a 4 inch pipe, but I don't find one for a 3 inch pipe.
 
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DanFL

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Here's what I ended up doing, in case it can help anyone else. I found a PVC flange that would fit inside of a 3" coupling. I installed the 3" coupling on the existing 3" pipe, then dry fitted the flange to locate the holes, then pre-drilled the holes through the porcelain tile. All but one of the holes ended up in the void (tile was slightly overhanging the void), with one just barely in the existing concrete. I then installed masonry plastic sleeve anchors which were held tightly in place by the tile, then filled in the void with concrete which surrounded the anchors and the 3" coupling. When the concrete was set, I glued in the flange and screwed it down. Very solid installation now with no movement.
 

Jadnashua

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While they make them, an inside fit flange on a 3" pipe is not recommended. They tend to cause clogs. It may work fine. The ID of the horn on most toilets is a bit over 2", and with the inside fit flange, you have 2.5". Depending on the design of the toilet, some of them are trying to make a nearly 90-degree bend right at the flange...that smaller ID can make a difference.

Second, most plumbers do not like to use an all-plastic flange. If you overtighten the anchor bolts holding the toilet, or the toilet gets knocked, it's all too easy to crack the flange. Over time, even if not actually overtightened, the plastic can bend from the tension, and loosen things up.
 

wwhitney

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Jim, I think you misread the post before yours. Dan is describing a 3" spigot end closet flange, he says it fits inside a 3" coupling. Its internal diameter should be the same as a 3" pipe.

I infer that Dan's narrative skipped over the step of cutting back the existing 3" pipe stub with an internal pipe cutter so that the coupling would be at the correct elevation.

Cheers, Wayne
 

Reach4

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Dan is describing a 3" spigot end closet flange, he says it fits inside a 3" coupling. Its internal diameter should be the same as a 3" pipe.
I had missed that too. I guess if the PVC flange fails some day, he could apply a repair flange with tabs over that.
 

DanFL

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Wayne is correct. I used an internal pipe cutter to trim the 3" stub back to the proper height and then glued the coupling. The flange then fit inside of the coupling and did not reduce the pipe diameter as I was concerned about doing this and already decided I would not use the kind that fit inside the 3" pipe.

Regarding the PVC flange vs. stainless, I decided to go with PVC because I previously read (on this or another forum) about potential problems with the stainless variety failing due to moisture exposure and corrosion. Seems that most stainless steel items that I find these days come from China so forgive me for being skeptical, but I just don't trust it. I recently bought some "stainless steel" screws from a big hardware store - made in China. They have been installed for less than 6 months are are already corroded. So I just didn't trust the stainless steel flange either.
 
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