Summary: Learn how to make repairs to flashing, repair cracks and small holes in flashing, repair flashing mortar joints and replace damaged flashing.
Where one part of the roof meets another part or where the roof buts onto a wall, the joints are weatherproofed with ‘flashing'. There are different types of flashing for different types of joint.
Flashing comes in several materials: lead, zinc and bitumen (used on felted roofs).
Lead is the best material to use as it weathers extremely well and can be used on all types of roof. Zinc is less expensive but does not last as long as lead, and can be difficult to work.
Fine cracks in flashing can be repaired by injecting a bituminous sealant into them with an applicator gun. Large cracks and small holes will need to be patched with a self-adhesive metal-backed flashing-strip.
With a paintbrush apply flashing-strip primer over the damaged area and 50mm beyond.
When flashing is fixed in place its top edge will be fitted into the mortar between two courses of bricks. The flashing can sometimes work loose at this point and water can penetrate under the flashing and into the mortar joint.
If the flashing springs back after being pushed into the mortar joint, wedge it in place with small pieces of wood.
If an area of flashing is badly damaged or corroded it should be removed and replaced with self-adhesive metal-backed flashing strip, which, unlike lead flashing, is not fitted into mortar joints between courses of bricks.
Use two lengths of flashing strip positioned in place so they overlap the roof and wall/chimney stack by an equal amount.
For internal corners, make a small cut in the lower edge of the strip, overlapping the cut edges.
For external corners, cut a square patch to fit over the corner. The square patch must be fitted before the main strip as shown.
Join an existing conversation or create a new thread related to Roof and guttering in our DIY forum.