Can a cracked chimney pot be replaced?

Clay pots crack for ordinary reasons. Frost gets into a saturated pot and splits it, the flaunching around the base fails and water pools, or old age and heat take their toll. Not every crack means a new pot.

A fine crack in the surface or the glaze, with the pot still firm and the flaunching sound, can be watched. A crack that runs the full height of the pot, a pot that rocks when pressed, a section missing from the rim or fragments falling into the flue are different. A split pot can drop pieces into the flue and cause a blockage, and a loose one can come down in wind. Water also gets into the stack through the crack and keeps the masonry wet.

The practical test is simple: if the pot is still whole and stable, it can often be repaired by renewing the flaunching. If it is split, loose or missing pieces, replace it. A roofer looks at it from a platform at the top of the stack, not from the ground, because cracks are hard to see from below.

The roofer chips out the old flaunching, the mortar collar around the base, and lifts the damaged pot away. Any loose mortar or crumbling brick on the stack top is cleaned and made good, so the new pot sits on a firm bed. Then the new pot is bedded in mortar, set upright and level, and the flaunching is laid around it.

The flaunching is shaped into a smooth slope that sheds rain away from the pot and off the stack. The edge should project slightly so water drips clear of the brickwork, rather than running back under it. A well-made collar is solid, sloping and free of gaps where the mortar meets the pot. How the flaunching is made, and why it cracks, is covered in our guide to chimney flaunching, which is the right page for the mortar side.

A job for one pot is quick compared with most stack work, but the access still matters, so the platform is part of the quote, along with the pot and the mortar.

Pots come in many forms: plain round pots, tapered ones, tall cannon-head pots and others with decorative rims. On an older house the pots are part of the look, and a mismatched replacement shows from the street. We match the style, the height and the colour as closely as we can, and on a stack with several pots, we compare them side by side before ordering.

Fit matters too. The pot has to suit the size of the flue it sits on and the appliance below. A gas fire, an open fire and a stove can have different needs at the top of the flue. If a pot is replaced without a cowl, there is a chance of nests and rain; if a cowl is fitted, it must suit the appliance. Our guide to chimney pots, cowls and caps goes through the fittings.

Pots are part of a period house's character, so like for like is the sensible default, and the council should be asked first if you want a different type on a protected building.

With a pot lifted, the roofer can see what is underneath, and that is often more useful than the pot itself. We look at the top course of brickwork, which may be loose or spalled, and at the state of the flue liner or the top of the flue. Water from a damaged pot may have run down the stack and attacked the flashing at the base, where the brickwork meets the roof covering, so that gets a look too; if it has failed, our note on chimney flashing replacement explains the repair.

Brickwork that is crumbling at the top of the stack may need rebuilding a few courses before the pot goes back. Our guide on spalling chimney bricks covers that, and it is far better to find it now than to bed a new pot on a failing top.

It is also the moment to clear the flue of debris from the old pot, and to decide whether a cap or guard should go on to stop the next nest. A flue that is not in use may be better capped and ventilated.

After the survey you receive a written quote that covers the pot, the mortar, any brickwork repair and the access, so a replacement can be weighed against renewing the flaunching alone. Photographs from the survey show the cracked pot and the state of the stack top.

Where several pots are cracked, replacing them together is cheaper than coming back, because the access is shared. If the roof or flashing also needs work, one visit and one scaffold can cover all of it. Our 10-year workmanship guarantee is issued in writing once the job is done, and the old pot leaves with us. Ask for the pot's height and diameter to be written on the quote, so the delivery can be checked against it before anything goes up. For the rest of the stack, see chimney repairs in Stroud.