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Summary: How to change a cast iron soil and vent pipe for plastic,
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Joining new plastic toilet connections to old cast iron waste pipes is a very common problem encountered by DIY enthusiasts. The difference in the pipe diameters and the rigidity of cast 
iron soil and vent pipes makes it very difficult to cut into them to add a new toilet or even the waste pipe from a wash hand basin or shower. Although cast iron pipes can be drilled to accept a new waste pipe and can also be ground down to accept a 100mm waste pipe collar, it is ultimately cheaper, in most circumstances, to change the cast iron pipes for a new plastic soil and vent system.
This is a long and detailed project divided into two parts and covers not only the fitting of the external waste pipework necessary for fitting a new toilet. The work required to fit 32 or 40mm solvent cement waste pipes for hand basins, sinks and shower waste pipes can be seen by clicking here and part Part 2 of the project can be seen by clicking here.
The first thing that needs to be done is to remove the existing soil and vent pipe. Do not do this until you have either drawn a diagram of where it went of taken a digital photograph. Later on you will see that it is important to put things back where they were as they will have been installed to building regulations and, unless a complete revamp is required the position should not be altered too much. Although we did not photograph the existing pipework you can see from the image on the left how a typical SVP layout is fitted.
Just above the horizontal grey pipe you can see a couple of pink dots. This is where the old cast iron toilet waste came out of the building together with the waste pipe from the wash hand basin. A new bathroom has been created to the left of the old one, hence all the pipes need moving.
A cast iron soil and vent pipe is a very heavy thing! Take the utmost care when removing the old one and always wear safety gloves and goggles. Very often the only way to remove and old pipe is by brute force and hitting the cast iron with a lump hammer will shatter it relatively easily but will create dangerous shards of iron. There is a cast iron hopper to the left of the window in the picture above. This hopper collected the water from the old bath waste (see the pink dot above the hopper). This was also removed later as a new bath waste was connected to the new plastic waste pipe.
Sometimes old soil and vent pipes can be made of cement fibres which look very much like asbestos. If you have any doubts as to their origin contact your local council for advice. Break all the existing pipework down to ground level where, at some point under the surface you will see that the soil and vent pipe is connected to a clay pipe which will take it to the nearest foul manhole.
In this instance the clay pipe was near the surface and by removing the old cast pipe the collar of the clay pipe broke off. It was necessary, as it probably will be with the job you undertake, to excavate around the clay pipe and give yourself plenty of room to cut the top of the pipe off square to allow a good connection to be made. The walls of the old clay pipes and cast pipes are a lot thicker than the new plastic pipes. Although the internal diameter is very nearly the same, the external diameter varies a great deal. The external diameter of a new plastic drainage pipe is usually 110mm but the diameter of a cast iron and/or clay pipe can be up to 136mm. This is where the difficulty in joining the two arises but fortunately these days it is overcome quite easily. When fitting a new soil and vent pipe always work out where your start (toilet) and end (ground connection) points are and draw the system you intend to install. This will allow you to work out how much pipe and what fittings you need. If you can see the finished job in your minds eye before you start it will be much easier to install.
This image shows a flexible rubber connector which can be bought from the top tools box you can see below. The principle is simple as you just slide the connector over both ends of each pipe and tighten the jubilee clips. THis gives a watertight joint which is also flexible enough to allow for ground movement. Joining pipes and connectors is not as easy as it sounds and the fittings for plastic pipes are made to be totally water, and in a lot of cases, air tight. This means they fit together very tightly and 99% of the time some lubricant is required to ease one part of the fitting into another. Historically Fairy Liquid has been used as a lubricant for fitting pipes to pipe fittings but this has a habit of getting everywhere and making tools, hands and everything else very slippery. It is much better, when buying your pipes and fittings to buy a tube of pipe joint lubricant. Smear the lubricant on both sides of the work and it will slide home easily.
When you have dug down and cut off the clay pipe to the required height you can fit the flexible connection sleeve. Undo the top jubilee clip so it is loose enough to allow the soil pipe to be dropped in and tighten the bottom clip us as tight as it will go. If you have to leave the clay pipe for any length of time because you need to go to the builders merchants, or even have your dinner, screw up a plastic bag with some newspaper in it to form a bung in the top of your pipe. If any debris is allowed to fall down into the pipe it will find its way into the manhole, or worse, to a bend before the manhole, where it will cause an obstruction which will later turn itself into a blocked pipe.
As we move up the wall making each fitting secure it is important that pipe brackets are fitted at regular intervals. We always fit brackets to vertical runs of pipe every two meters, and to horizontal runs, every meter. If there is a pipe fitting such as a bend or branch, a pipe bracket is always fitted either side of the fitting. It is much better to have too many pipe brackets than not enough.
When a length of soil pipe is cut the end is left fairly sharp and burred. It will not matter how much lubricant you put on the end of this, it will just rip out the rubber joint of the receiving collar. The end of a cut pipe should be filed to a shallow chamfer to make sure the pipe slides easily into the joint. You can see from the image left we have used a 4 inch grinding wheel to create our chamfer but this can easily be done with a rasp file or even a sheet of rough sand paper
. Unfortunately when you do this kind of a job for a living time is of the essence so speed of work is very important!.If you do use a grinder please make sure you have the correct safety equipment on and always use the grinder so the blade is throwing any waste away from your body.
Using the lubricant mentioned above, push the first length of pipe into the flexible sleeve connection and tighten the pipe bracket. This first, short section now forms the basis of all other connections as ultimately, this is where the whole system ends up. You can see from the image on the right we have now concreted in the connection and tightened the wall bracket to make sure our starting point is a solid place to work from. We try and get to this point at the end of a day so the concrete has a chance to go hard overnight. See our mixing concrete project for help on getting the right mix for this, and many other jobs.
From here on in it gets a little trickier as we have to join both ends to make the system. It is now time to work out exactly where the pipes have got to get to and where they will join up. If you are fitting, as we are, a new bathroom, with the toilet in a new position you will need to work out where you want the toilet and drill the hole for the new waste pipe. This is best done with a 15omm diamond core drill bit and a heavy duty drill, both of which can be hired from your local tool hire centre. It will cost you about £40.00 for both tools for a days hire but you if you try to do this any other way you could be on this job alone for days. If a job is worth doing it is worth doing well and with the right equipment you will only have to do this once. If you try and make the hole by by hand with a hammer and chisel you will wish you had not.
Put the back of the toilet to the wall and measure the distance between the toilet outlet and the wall. Now add to that the distance from the inside surface of the wall to the outside surface and cut a piece of pipe that long. Chamfer both ends as described above. Now slide on a 90 degree easy bend as seen in the left hand image and place the completed pipework into the hole in the wall. As you can see, using a 150mm drill bit gives you a little room for maneuver which you will be grateful for later on. All of the existing holes on this job were temporarily filled with expanding foam to stop the cavity getting rain soaked and later we went back and replaced the holes with new, matching bricks. See our project on replacing a damaged brick.
Its now time to click through to part two of the project. Please click here.
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