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Four easy ways to wreck your terrace

Victorian era houses such as those found in Darlington and Chippendale were built from relatively porous materials compared to modern building materials. The bricks, mortar and render of Victorian houses absorb small amounts of moisture which then evaporates into the atmosphere. In other words the house “breathes” reports John Berry in the South Sydney Herald in October 2009.

Many renovators and builders mistakenly believe that when restoring a terrace, the best thing to do is to replace the old porous building materials, particularly the old lime based mortar and render, with modern cement based materials. This is in fact disastrous for the house because modern cement based mortar and render is not porous and does not breathe. Moisture still makes its way into the bricks but can become trapped by the modern mortar and render. The trapped moisture can then cause the bricks to decay. Very costly repairs down the track are the result, or if the damage is severe the building will have to be demolished.

Help protect your Victorian house and preserve what is left of the architectural heritage of our suburbs.

1. Do not use modern cement bases mortars and renders to make repairs. Use traditional lime based mortar and render, which “breathes”. Also, if there is any movement in the walls, modern cement based mortar is inflexible and will cause the brickwork to crack.

2. Do not replace a timber floor structure (which allows the building to "breathe") with a concrete slab. Concrete slabs trap moisture and forces it up into walls and causes decay in brickwork, mortar and sandstone. These slabs also force moisture up into the common walls, thereby causing dampness in your neighbour’s house.

3. Do not repair or cover sandstone foundations and walls with modern mortar or render, which will trap moisture and salt that rises from the ground, causing decay of the sandstone. A “sacrificial” layer of soft lime based mortar should always be used for repairs, which will absorb the moisture and salts and eventually decay, thus sparing the sandstone. The sacrificial layer can then be replaced.

4. Do not use modern plastic paints. They are not permeable and do not allow the walls to breathe. If possible, old-style permeable lime-wash paints should be used. If sourcing lime paint is difficult or cost prohibitive, modern flat acrylic paints can be used providing the old paint is removed and only two layers of acrylic paint are applied.

A recipe for lime mortar can be found at the link below, but caution should be taken in making the mixture. It is recommended that you seek the advice of an architect or builder who specialises in the restoration of old buildings before a restoration project. – then follow the link to Twelve tips on caring for old buildings.

Photo: Andrew Collis - The writer outside his terrace in Darlington