A chimney stack faces weather from every direction with none of the shelter that the rest of a house benefits from, and over enough winters this takes a visible toll on the brickwork itself. For many properties in Horfield, the first sign that a stack needs attention is a scatter of small brick fragments found on the roof or in the guttering below, long before any leak has actually made itself known indoors. Because it develops slowly, spalling is easy to miss until quite a few bricks are affected, which is why periodic checks are worth doing even when there is no obvious sign of a leak.
This is spalling, where water that has soaked into a brick freezes and expands, cracking and pushing off the outer face of the brick. It tends to affect the most exposed side of a stack first, usually the side facing the prevailing weather, and once it starts it will continue to worsen with each cold winter rather than settling down on its own, gradually eating further into the brick with every freeze-thaw cycle.
Unlike a mortar joint, a spalled brick cannot really be repaired in place, since the damage has affected the structure of the brick itself rather than just the surface. The only proper long-term fix is replacement, cutting out the damaged bricks and installing new ones bedded in fresh mortar. Attempting to patch or render over spalled brickwork tends to trap moisture and can make the underlying problem worse, effectively hiding rather than solving it. In some cases a brick can appear only lightly affected from a distance but turn out to be considerably more damaged once examined up close, which is why photographs alone rarely give a reliable picture.
Matching replacement bricks to the existing stack matters for both appearance and performance. Horfield has a good deal of housing built across different eras, and matching the size, colour and texture of older brick can mean sourcing reclaimed stock rather than simply picking something off a modern supplier's shelf, particularly for pre-war properties where the original bricks may no longer be produced at all.
Because spalling is usually a symptom of water getting into the brickwork in the first place, it is worth checking the surrounding mortar and any nearby flaunching or flashing at the same time, since these are often part of the same underlying cause. Replacing bricks without addressing why they got wet in the first place risks the same damage reappearing in a few years, undoing the benefit of the repair. This is also a good opportunity to check the condition of the flaunching at the top of the stack, since problems there often accompany, and sometimes cause, brick damage lower down.
If your Horfield chimney has bricks that look cracked, flaking or crumbling at the edges, it is worth getting it assessed sooner rather than later. Brunel Roofing Bristol offer free inspections and can advise on the right scope of brick replacement, all covered by our 15-year guarantee.
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