It’s vital to keep chimneys in good order, particularly in older properties. With the widespread use of central heating and rarity of log fires, many chimneys are now an unnecessary addition to a property. A loose component of a stack may be prone to collapse in high winds and other inclement weather, which may well lead to untold damage to property (or individuals) below.
Never attempt any repairs to chimneys unless the stack is little and easy to reach from a roof ladder or if you’ve hired correct chimney scaffolding.
Because chimney stacks are in a really blocks play and learn exposed position, it’s common for the pointing between the bricks to crumble away. This can lead to dampness and make the stack unstable. Damaged joints will have to be re-pointed:
First rake out the old mortar to a depth of about 20mm and lightly wet the points. A garden sprayer is ideal for this. Then press fresh mortar in place and smooth it off at a slight downward angle. The mortar really should consist of one part cement to five parts sharp sand, with a bit of PVA adhesive added to enhance its adhesion and workability.
An additional vulnerable spot is the mortar (known as flaunching) around the chimney pots. If there are cracks but the pots themselves are still held firmly in place you can fill them by injecting non-setting mastic. However, if the flaunching is loose you’ll need to chip it away – with care – and replace it with new mortar. Use one part cement to four parts sharp sand, once more with just a little PVA adhesive. Spread the mortar around the pots, building it up around the base and smoothing it so that it slopes down to the edges of the stack. This will allow any rainwater to drain off quickly.
Cracked chimney pots can occasionally be repaired with silicone mastic; otherwise they’ll have to be replaced. In the event you have an old home you could be able to get suitable pots from a demolition contractor or architectural salvage yard. To fit the new pot, chip away the old flaunching and replace it with new mortar, as described above.
If the flues are no longer used, you are able to fit ventilator caps to the pots to stop rain obtaining in. Alternatively, you are able to remove the pots and make the flues rainproof by bedding airbricks around the sides at the top and laying paving slabs over the flues to throw rainwater clear of the stack. The airbricks ensure a gentle supply of air to the flues to keep them dry.