Maintaining a chimney

When making repairs to the roof, it is always a good idea to check the condition of the chimney as well. Loose pots, cracked Warning Chimney pots are larger and heavier than you might expect, so handle them carefully and, if the pots are sound, take care not to crack them as the flaunching is chipped away. In old houses it is not unknown for the chimney pots to drop into the flue when the over the top of the chimney so it is about 60mm thick against the base of the pots and slopes down to about 20mm thick round the edge of the stack; form a gentle curve all round to throw water away from the pots.

Replacing pots

Cracked or broken pots must be replaced since they may be displaced in a gale and cause damage to the roof or injure people below. To find the size of the pot required, remove part of the bedding mortar and measure from top to bottom and the internal diameter at the top; if possible, the replacement pot should have a square base so it fits exactly over the flue opening in the stack. To replace a pot, remove all the flaunching as previously described, place the new pot over the flue opening and apply new flaunching mortar. if you are working on an old house, you may find the base of the new pot is too narrow to rest o’ver THE flue opening. In this case straddle the edges of the opening with pieces of roofing slate to restrict its size to a suitable width and support the pot on these. Where the base of the pot is built into the brickwork of the flue, you will have to remove bricks to release the pot; fit the new pot by replacing the bricks around IT.


If the chimney is no longer used, you can cap the flue to make it weatherproof, but it should not be tightly sealed or the flue will become damp and spoil wall decorations in rooms through which it passes. Metal and clay capping cowls are available. The metal type simply clips into the top of the chimney pot; the clay ones, which are longer lasting and less obtrusive, are secured with cement mortar between the cowl and the inside of the pot. When a disused flue has cracked pots or flaunching, it is best to remove the flaunching and pots and seal the flue with one or two paving slabs. Before fitting the slabs, knock out at least TWO bricks from the sides of the flue and replace them with airbricks. Bed the slabs on mortar so they are level and overhang the sides of the stack by at least 25mm all round. Alternatively you can lay slates over the flue after fitting the airbricks and cover the entire surface with new flaunching.


As long as you will never use the chimney again you can reduce the height of a chimney stack if you feel this will improve the appearance of the house or If the stack is dangerous and in need of repair. It is essential to erect scaffolding round the chimney or to work from a scaffold tower when possible. Use a club hammer and bolster chisel to remove the bricks course by course from the top down to the required height, taking care to prevent rubble falling down the flue. It is a good idea to tie a long length of stout string to the handles of the tools and tie the string firmly round the base of the stack; if you drop the tools down the flue, you can then retrieve them easily. Place the bricks in a bucket and lower them to the ground as work proceeds. At the top of the lowered stack, relay one or two courses of bricks to overhang the general brickwork surface slightly; this will help to throw water clear of the stack. Finally cap the flue.


If the mortar joints between the bricks of a chimney are crumbling, they must be repointed using the same technique as for repointing walls. After repointing or sealing a stack, it is a good idea to paint the brickwork with a clear silicone water repellant to prevent rainwater penetration. CRACKED BRICKS

These can often indicate serious faults and you should seek the advice of a builder or roofing specialist. Bulging brickwork or cement rendering should also be referred to a specialist.

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