Benefits of using lime mortars
Traditionally (up to around the 1930/40’s) most brick buildings and structures were built using solid brick walls with a lime mortar. During periods of rainfall, the walls absorb the moisture like a sponge which then dry out afterwards by natural evaporation. The most effective route for this evaporation to occur is through the permeable lime mortar joints which, being more porous than the bricks, act like a wick drawing the moisture from within the wall to the surface allowing it to evaporate. This is often described as “allowing the wall to breath.”
However, if a harder less permeable cement based mortar was used to build a solid wall or repoint brickwork originally built in lime mortar, then the moisture would be unable to be released through the joints therefore trapping the moisture within the bricks. The resulting moisture movement is then concentrated within the bricks which can cause problems such as saturated brickwork and potential damage due to the movement and crystallisation of soluble salts or frost damage.
Self healing properties of lime mortars
All brickwork walling naturally moves due to a number of reasons which can include moisture movement, structural loading and creep, thermal expansion and contraction, movement due to ground conditions (settlement and heave) and other external forces.
Where this movement is small, it is often taken up as many fine cracks within the mortar joints of lime based mortars. However, if a strong cement mortar is used then the cracking may occur as large cracks within the mortar joints or even through the bricks.
Lime mortars can also have a self healing capacity which contributes to their durability. This self healing is due to the ability of ‘free’ lime in the mortar being dissolved by water penetration and then transported to the site of the cracking where when water evaporates this ‘free’ lime is deposited beginning to ‘heal’ the crack.
Ecological benefits of using lime mortars
Lime mortars absorb carbon dioxide as they cure.
Lime is made at a lower temperature than cement therefore it requires less energy to produce resulting in less carbon dioxide output (less embodied energy).
Brickwork built using lime mortars can be easily recycled and reused in the future unlike cement bonded brickwork.
In a future Blog, I’ll talk about the different types of lime mortars available for the building and repointing of brickwork.