The joints in cast-iron gutter systems are held together by nuts and bolts which are usually screw-headed. A proprietary sealing compound – often a mixture of putty and red lead or a mastic sealer – is sandwiched between the two ends to make the joint watertight.
A leaking joint may be patched up by cleaning the area with a wire brush and applying one or two coats of bituminous paint. However, for a more permanent repair the section on one side of the leaking joint must be removed, cleaned and replaced. If the removed piece is in the middle of a run, two new joints have to be made – one at each end of the section.
Start by removing the bolts which hold the joints together. These may well have rusted and seized – in which case apply penetrating oil to loosen them. If this fails, saw through the bolts with a junior hacksaw. With Ogee-section guttering, remove the screws holding the section to the fascia as well.
Lift out the loosened section – making sure as you do so that its weight does not catch you off balance – and take it to the ground. Returning to the guttering, chip off all traces of old sealing compound from the hanging end and scour it thoroughly with a wire brush. Repeat the cleaning operation on the removed section.
Apply fresh sealing compound to the socket section of the joint, spreading it in an even layer about 6mm thick. Relocate the removed gutter section, screwing it to the fascia or laying it on its brackets and fitting the joints together.
Insert a new galvanized bolt into the joint from above. Screw on its securing nut, tightening gently so that the joint closes up and squeezes out any excess compound. Trim away the excess with a putty knife, wipe over the area with a damp rag, then repeat the operation for the other joint. Finally, repaint the joints with one or two coats of bituminous paint.