Over time, the mortar between brickwork joints can weaken, crack, and fall out. Missing mortar can lead to water ingress and damp problems and should be addressed as soon as the problem appears. In the case of chimney stacks, missing pointing can eventually lead to structural issues that may require a full or partial chimney rebuild.
Fortunately, repointing brickwork to make mortar joints watertight is a relatively simple and low-cost process.
The chimney repointing process starts with removing mortar from the affected areas to a depth of 25mm. An angle grinder is normally used for this, but hand tools may be preferred where the brickwork is particularly fragile or other restrictions prevent the use of power tools.
Once the joints of the chimney brickwork are raked out to the correct depth and loose material is removed, new mortar pointing is trowelled into joints using a 5:1 sand and cement mix, or a stronger 3:1 mix for chimney stacks that are particularly exposed.
When inspecting the condition of chimney stacks, special attention should be paid to the joints of flashings.
Chimney lead flashings including step flashing, aprons and back gutters are returned into brickwork and fixed with lead wedges or lead fixing clips. It is important to ensure that the joint where flashing are returned into the chimney stack is intact and watertight.
It is often the case, especially in older properties that flashings are pointed with mortart which is prone to cracking. A better option is lead sealant, a silicone based product elastic enough to withstand some movement and less prone to cracking than mortar. Monitor the pointing of leadwork around a chimney stack regularly to ensure it remains in good condition. If mortar joints need to be repointed, take the opportunity to replace mortar with lead sealant.
Daniel James Construction are experts in chimney repairs and maintenance with expert teams covering London and the South-East. Get in touch today for advice and assistance with chimney repairs and maintenance.