Roof Leaks: Avoiding Roofing Problems

Moisture seems to have a capacity to get in almost anywhere, and keeping out damp can prove quite a problem in older homes in particular. However, both traditional and modern methods can often be allied to keep the home dry and free from water damage.

Flashings consist of various types of watertight joint outside homes. These are used where chimney stacks come through roofs, where a roof abuts a wall, or around roof lights and dormer windows.

The traditional flashing materials are lead, zinc and copper. However, lead-beating is a skilled job calling for special tools. Though this is not necessarily beyond the skill of a handyman, other materials are easier to work and can usually be used. Both lead and zinc may deteriorate in time and need replacement.

Aluminium-based flashing, such as Evode Flashband, and mastics, can often be used for repair and replacement. Mastic glazing tapes and cords can also be used to effect repairs to deteriorated flashing.

Another type of flashing material is a pliable bituminous sheeting which can be softened with heat and manipulated to replace damaged areas.

The intrusion of damp into areas such as chimney breasts, the loft or an attic ceiling or bedroom is an indication that all is not well. The best time to detect the source of the trouble is during heavy rain.

In some cases, porosity of brickwork may be the cause, or a joint in zinc or other metal sheet may have lifted. Mastic or cold asphalt may be used to effect a repair.


A roof ladder is needed to carry out repairs to chimneys. A form of flashing around chimney pots is the sloped mortar fillet called flaunching.

This may have cracked and broken away as a result of normal expansion and contraction of the fabric of the home. While these are natural conditions in any structure, they are more intensified near sources of heat, such as chimneys.

Careful inspection may show that slight damage can be repaired with a mastic, or damage patched up with new mortar. Where patching up of damaged or deteriorated flaunching using mortar still does not solve the problem, you may have to remove and replace the entire flashing.

In older homes, the flashing around the base of a chimney may be a mortar fillet or haunching. Modern flashings consist of stepped, side flashings, with a gutter flashing at the chimney top and an apron flashing at the bottom of the chimney. The stepped flashing is cut into steps and inserted into mortar joints down the side of the chimney.

Lead is a malleable metal and made in various weights. 1.81kg lead is needed for roof purposes. The brick joints should be raked out and the new flashing cut with metal shears and inserted. Small pieces of rolled lead should be inserted to fix the flashing into position and the joint re-mortared with a 1:3 mortar mix.

When repairing mortar fillets use a little adhesive to bond new mortar to old. Make sure that you brush off any algae.

Cracks, however, may open up again, and some bituminous mastic or a flexible compound should be used. This can be applied with a special ‘gun’, so that the joint is effectively penetrated and sealed. These mastics may also be applied by trowel from a tin.

When removing old mortar from a chimney, rake out a single section of the stack at a time to a depth of 15mm-20mm. Before repointing, dampen the joints and form a weather-struck joint.

Damaged flaunching should be chipped away and replaced. Use a club hammer and chisel and work carefully, avoiding cascading large chunks of mortar down the roof. Keep a bucket handy and place the broken mortar pieces in this.

Chimney pots

It may be necessary to replace or refix the chimney pot. If you do have to remove this, seal up the fireplaces below so that dirt, dust and soot do not damage furnishings and fabrics.

Once you have removed the old flaunching, locate the chimney pot back into position, dampen the surround and apply a 1:3 mortar mix with a high-alumina cement and a little PVA adhesive to assist bonding, for new chimney flaunching.

This might be the opportunity to replace a chimney pot with a terminal if a modern heating appliance is employed, or to cap off a chimney if the fire is no longer in use. Modern terminals are usually made of a light weight material and easy to handle.

Chimney pots are usually heavier than they seem, so you may need help, if you have to lower it to the ground. If one crashes down, considerable structural damage may be caused, and someone could be injured.

Secure the pot with a stout rope, fixed round the stack. It is advisable to organise help so that you can lower the old pot to the ground.

You may have to fit pieces of slate or tile around a new pot to make it vertical. Use a spirit level to check this. Make sure that the new mortar fillet fills the gaps between the base of the pot and brickwork, and take care that mortar does not go down the flue. You can also fit a cowl to an existing chimney.

10. November 2011 by admin
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