How to connect a plastic pipe with cast iron

Sometimes when carrying out plumbing work it is necessary to connect pipes made from different materials. So, for example, the metalplastic pipes used today should be connected to pig-iron. This is usually required when you need to connect the sanitary pipes of the apartment water supply system to the sewage system. In old houses, the risers are made of cast iron, and therefore the question of how to connect a plastic pipe with a cast iron one is quite vital.

From a technical point of view, the methods will be somewhat different, and therefore it is worth considering separately each of them.

Simple connection

First of all, it is necessary to assess the condition of the cast-iron part intended for connection. If the strength is at a sufficient level, then you can proceed to work.

• First of all, you need to remove the old metal pipe. After that, it is necessary to assess the condition of the pipe to be connected. If it is durable, smooth and has a bell, then you can begin to work.
• All rust is removed from the inside of the pipe. To do this, you can use a metal brush and coarse sandpaper.

• Then a special rubber insert is inserted inside. It will act as a compactor. It must be recalled that before inserting a sealant on the adapter must be applied.
• After that, a plastic tube is inserted into the cuff, and to a depth of at least 5–8 cm for the greatest reliability.

This method is relevant only if the pipe has a special expansion socket. If not, then a slightly different method is used.

• The upper part of the pipe is cut with the help of a grinder, after which the end face will need to be processed with a file and sandpaper to remove all the burrs.
• Then a special adapter is installed on a cast-iron pipe, on top of which a plastic socket is put on.
• Further, the above steps are repeated. The connecting element is inserted, inside of which, in turn, a plastic pipe is mounted.

Caulking flax underwrap

As another method of connecting pipes, mention can be made of a caulking method with a sanitary roll. The method is simple, but requires experience.

• First, a sanitary winding is wound on a plastic pipe in several layers. The result should be a thickness approximately equal to the diameter of the cast iron pipe.
• Plastic pipe with a winding is inserted into the cast-iron.
• After that, a certain amount of winding is caulked into the gap between the connected pipes. For these purposes, you can use, for example, a narrow spatula.
• Then the remaining space of the gap between the pipes must be filled with a special solution. For its preparation, you need to mix the PVA glue and cement, diluting to the desired consistency with water. 

The resulting compound will be suitable for use in a day - two, when the mixture finally dries. The described method is relatively simple to use and is available. To use it, no special tools are needed, and all the necessary materials are available. Tubes connected in this way for a long time remain airtight, and in the event of a leak, you can always staking some additional amount of winding or apply a solution.

Compound using silicone sealant

It is worth saying that the above method was widely used before the advent of silicone fillers. Today, the popularity has received a slightly modified version.

• Before connecting the cast iron pipe must be well dried and cleaned.
• Then the pipe wrapped with plumbing thread must be inserted into the cast-iron socket to a depth of 10 cm.
• After that, the required amount of silicone sealant is fed to the remaining gap using a special mounting gun.
• Then the compound is left for about a day to freeze the silicone, after which the water supply can be used. 

The described method is much simpler than the previous one and to some extent preferable, since silicone decomposes longer. This means that the joint will be airtight longer.

Combined method

Each of the described methods has its own specifics and advantages, but nothing prevents you from using the combined method when connecting pipes. For example, a pipe can be wrapped with linen underwrap, but instead of caulking a gap, fill it with silicone sealant. You can experiment here, so everyone can find a method for themselves.

Press connection fitting

Another way to connect pipes of various materials is to connect using special connecting elements, called fittings.

• First, the cast-iron pipe (regardless of whether it has an expansion or it without a socket) is cut with a grinder. The cut end must be processed with a file and sandpaper to remove burrs.
• Next, the outer surface of the metal pipe must be coated with engine oil or grease.
• Then, using a special tool, an external thread is cut.
• After that, a sanitary thread is wound on the thread, over which the connecting fitting is wound.
• On the other side of this coupling element, a plastic tube with a compression sleeve is put on. It must be remembered that all sealing rings must be in place.
• Using a special tool crimped coupling. 

This method is reliable, durable and durable. Its application requires some effort, but the result will be valid for quite a long time.

Tip! Do not forget to be attentive to the little things and be sure to follow the safety instructions.

Video

If you are going to make the transition from iron sewage to plastic, you have to perform caulking a fan tee. This video shows how to do it. You will also see how to connect the plastic and cast iron pipes.