Cast-iron downpipe repairs

Cast-iron downpipes are usually attached to walls by pipe nails driven into metal, lead or wood plugs. The nails run through cast metal brackets some of which have spacers behind to prevent contact between the pipe and the wall. Brackets often come loose, making the pipe dangerous.

To secure a loose bracket, start by removing the bracket nearest to the ground and repeat the operation up to and including the bracket that is loose. To remove a bracket, lever out the nails with a claw hammer. Use an offcut of timber held against the wall to obtain the necessary leverage. Withdraw the section of downpipe. Where the joints have been sealed and do not fall away easily, heat them with a blow lamp to loosen the sealing compound or chip the compound away by hand.

Remove the loose plugs by digging them out of the masonry, and make up replacements – slightly larger all round than the holes – from pieces of 12mm dowel. If necessary, extend the holes with a 12mm masonry drill. Drive the replacement plugs into the wall until they are flush , check that they are firm, then refit the downpipe.

In many houses, downpipe joints are unsealed. If dirt collects in an unsealed joint, water may gather and freeze and crack the pipe. Avoid this by filling any unsealed joints with a mixture of red lead and putty or a proprietary mastic. Wipe it smooth with a rag then seal the joint with a coat of bituminous paint. Do the same with sealed joints that have become loose, having first chipped off the old compound.

Replacing a cast-iron section

If the whole system has eroded, it may be advisable to replace it with plastics guttering.

However, if the rest of the run is still in good condition, replacing a corroded cast-iron section is well worthwhile.

Where possible, take the old section to a builder’s merchant and obtain a matching replacement. As well as the shape and diameter, check that the new section matches the existing joints. If not, buy the appropriate union at the same time.

Cast-iron guttering is normally sold in 1.8mm lengths, so the new section may have to be cut to fit. When measuring it up, take into account any overlap for the joints or new joint unions.

To cut it, lay the old section over the top of the new and use it as a guide. Mark the new section in pencil and lay a strip of masking tape along the mark, towards the waste side, to give a clearer guide. Cut the section with a large hacksaw.

Mark the positions of the joint bolt holes and punch and drill them to a diameter of 8mm before you fit the new section into place.

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