My house is built with prefab concrete slabs for walls and floors. These have been prefabricated with most of the plumbing and electricity tubes pre- installed inside the concrete.

While redoing the bathroom I drilled an 8mm hole right through one of these sewer pipes in the ceiling (I think it must be PVC since the part coming out of the ceiling is PVC). On the floor above we have a washing-machine and two bedroom sinks connected to this pipe (all pipes are inside the floor). If we open any of these taps, the water comes through the hole.

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How can I fix this? Do I really have to break away the concrete or could I get away with plugging the hole with silicone kit (being careful not to block the pipe above with excessive kit). Would it become a problem if the concrete keeps getting wet near the leak?

If I really have to remove the concrete, how should I do it? I guess that when I use a jackhammer it would only cause more cracks and leaks in the pipes?

Another option might be to saw the large PVC pipe, and try to fix the leak from the inside of the pipe, maybe with polyester or some epoxy type of product?

Edit: the pipe appears to be about 55 mm deep inside the concrete and is about 80 mm in diameter. The floor/ceiling is at least 200 mm thick (rough guess).

Edit 2: After talking to a professional contractor, his advice was to use some kind of chemical plug with two components. I don't know what the components are but it did sound convincing, and I'm willing to give it a shot if it saves me breaking up the whole cealing (which I can always do afterwards if it turns out to be a flop). He'll be doing it for me next week if I agree (special tools are needed, so it would not be economical to do it myself).

  • 1
    The chemical plug is doing well. We did saw the pipe to the right off in order to smear the residue out flat from the inside. It's working perfectly. I think (but not 100% sure) it was "fischer FIS EM Injection Mortar", not cheap but saved us quite some work. Aug 31, 2015 at 22:51

2 Answers 2


You're not going to like the answer, but the way to properly fix this for good is to break up the concrete, cut out and replace the damaged section of pipe.

There are a variety of ways you could break this up. A sledge hammer, a hammer and chisel, a SDS drill with a chisel bit, or a larger chisel like a Brute. If you have a ton of time on your hands, you could use a standard hammer drill and drill tons of little holes around the area to remove and then break it up with a smaller hammer and chisel. The concrete should not crack outside of the immediate area you are working on. As for the pipe, yes you might damage it further but you need to replace a section anyways.

Once repaired you would add new concrete and replace the finish (hard to tell from the pic).

Any other fix is unlikely to be permanent or without compromise.

  • Thanks, that's what I was afraid of... How does the chemical plug idea sound to you? (see my 2nd edit). According to the contractor silicone would never last, but the chemical plug would be more durable. Aug 4, 2015 at 23:32
  • I'm not sure what a chemical plug is, but sounds like some sort of epoxy (two parts). There are other methods too like inserting a liner into the pipe, but these alternative methods tend to be expensive. I'm not sure what the price difference is between the proposed "plug" and ripping it out, but you can try, and then spend more money fixing it, or just do it once and do it right.
    – Steven
    Aug 5, 2015 at 0:05

Assuming there is no toilet above, all the waste going through these pipes should be water only (maybe a bit of hair in the sink). If so, you may be able to plug the leak with a solid rod that fits the hole. The water should run easily around it.

You need to figure out if there is one hole in the pipe or two (did you punch through upstairs? Even if not, you may have hit the bottom and top of the pipe.) You need to be able to push a closely fitting rod, preferably plastic (but not polyethylene or other slick types), through both the lower hole and the upper one, if there is an upper one.

Once you have tested pushing the rod into the hole(s), take it out, sand it lightly to give it some grip, coat it with sealer, preferably silicone that can be used in wet repairs, and reinsert into the hole. Tape it in place. Do not use for 24 hours. Then trim the excess.

  • I don't think we punctured the top. Considering the rod, I'm afraid this would cause a blockage in the long run. Lint from the washing machine and hair (as you mentioned) would probably pile up behind the rod I think? Thanks for the idea though. Aug 4, 2015 at 15:15
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    Obviously, you don't need to push the rod all the way into the pipe in the last step. If you know the inside diameter of the pipe, you mark that length on the rod, so that it stops just inside the first wall.
    – Dave Tweed
    Aug 4, 2015 at 15:58
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    @DaveTweed Excellent point if he is confident only the lower section was punctured.
    – bib
    Aug 4, 2015 at 18:24
  • Thinking about it again, maybe the top is also damaged. The drill did go up with a thud. I very much doubt that the water ever fills the whole pipe at that point though. According to a professional contractor, silicone would never be a lasting solution, and would make other solutions much more difficult because it would contaminate the hole. I'll probably try a chemical anchor (see my 2nd edit). Maybe I should patch up the top of the pipe by carefully pushing up a pin with a blob of silicone on top, and try to do it without contaminating the bottom part of the hole (seems difficult though). Aug 4, 2015 at 23:47
  • if you were confident about the composition of the pipe, you could use the solvent appropriate to the material. The blockage in the pipe is far from ideal, but it may never clog, and if it does, you are no worse off than you are now.
    – bib
    Aug 5, 2015 at 0:03

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