How to Repair Cast Iron Pipes


There are three ways to repair iron pipes, depending on the extent of the damaged area, and on what materials you can get hold of.

If the damaged area is small and there is at least 25mm (1") clearance around the pipe, buy a single Johnston coupling and use this to seal the hole.

Where the damage extends over a larger area, you have two choices:

1♦ Cut out the old section of pipe and fit a new piece of cast iron pipe between two Johnston couplings or Primofit push-fit joints.

2♦ Unscrew the complete damaged section at the nearest threaded joints, and fit a new section using adaptor couplings. This may be easier where space around the pipe is limited, though you could have to remove several sections to get at the damaged one.

In this case, use plastic or stainless steel for the replacement section (but not copper, which sets up an electro-chemical reaction with iron that eventually causes the pipe-work to corrode). Choose the nearest matching diameter — eg 15mm plastic or 1/2" iron — then buy couplings to suit. There are versions for both stainless steel and plastic, with threaded joints on one side and compression joints on the other.

reparing a small hole in a cast iron pipe


For a small hole, saw through the pipe, ease open the cut and insert a Johnston coupling. Slide it over the cut and tighten the nuts with an adjustable wrench.




repairing more extensive damage to a cast iron pipeFor more extensive damage, cut out a section of pipe and fit a new piece. Use Johnston couplings or Primofit joints to avoid having to make threaded joints.

to replace a complete section of cast iron pipingTo replace a complete section, dismantle the run back to the nearest threaded joint. Clean the thread, wrap on PTFE tape, and fit a threaded adaptor …


then cut a new section of plastic or stainless steel pipe

… then cut a new section of plastic or stainless steel pipe and compression joint it to the adaptor. Repeat at the other end, then reassemble the run.






Modern joint fittings have made it possible to repair lead pipe without having to worry about traditional ‘wiped joints’. After cutting out the damaged section, simply join in a new section of copper pipe of the equivalent internal diameter.

The only difficult part is measuring the old pipe so that you know what size fitting to buy. Lead pipe varies in wall thickness according to its grade, so look for identification marks stamped on it giving the weight and bore size — eg ‘BS 602 3/4"x 11lbs’.

If you can’t find any stamp (very old pipe may not have one), either take the old damaged section with you to the merchants, or cut the pipe and then measure both the bore and the wall thickness.

When cutting out the old section, take care to support the pipe so that you don’t cause any damage further along the run. Remove any burrs with a file or metal rasp, then cut the new copper section to the exact size of the gap.

1. Saw the lead pipe with a hacksaw or coarse toothed ‘Universal’ saw. Cut far enough past the damage to leave you with the true size of the pipe.

2. Join in the new section of copper pipe using a pair of your chosen fittings. Take care to assemble them in the right order then tighten the nuts.

24. May 2011 by admin
Categories: Heating, Plumbing | Tags: , , | Comments Off on How to Repair Cast Iron Pipes


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