Lime or cement mortar?
This is specific to old buildings, and walls of similar construction.
These houses typically use soft bricks that break easily, often have
little in the way of foundations, sometimes none, and most have no dpc.
Skimpy foundations mean minor movement is a normal event for many old
Cement is not movement friendly, and with any wall movement cement
typically makes a single clean break. It has no self healing ability.
Normal wall movement thus results in broken walls, which compromise the
overall house structure, and require extra repair work.
Cement mortar is stronger than soft brick, so when movement occurs it
is the bricks that will break rather than the cement. Broken bricks
have their core exposed, and without the protection of the fireskin
these bricks will usually begin to slowly deteriorate due to wet freeze
cycles. Gradual erosion of the brick leaves the wall in need of many
bricks being replaced. Its a shame to see walls like this, knowing that
just a little more knowledge and no damage would have occurred. Theres
a building near here that has about half the bricks near ground level
badly decayed, and is now in need of large numbers of bricks replaced.
Lime mortar is weaker than the soft bricks, so when movement occurs it
is the lime that cracks, not the bricks. This is the better option. No
bricks need replacement.
When moved to breaking point, instead of forming a single break, lime
tends to form lots of microcracks. Lime then reacts with the CO2 in the
air to grow hard crystals across these microcracks, and thus rebonds
itself. It self-heals. Lime mortar is not flexible, but it behaves as
if it were in this way. Lime accomodates normal minor movement without
Old houses handle damp differently to new builds. Soft bricks are
porous, and rain hitting them soaks in a little. Interior condensation
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