Brick Repairs Due to Settlement and Shrinkage
This is a problem which may have been caused by imperfect foundations or movement of ground beneath the home. Common reasons are land on an unstable surface, such as an old rubbish tip, or building on clay subsoil, which moves in accordance with the amount of ground moisture.
Other reasons are rotted or decayed timber, which loses volume and causes subsidence. And tree roots affecting foundations. The roots of a tree roughly cover the spread of the branches. Roots may crack foundations or take moisture from the ground and cause soil to subside.
Subsidence is usually indicated by running cracks through brickwork joints. Gaps around door tops and window frames may be other indications, though these can be caused by natural shrinkage of timber.
There are two simple ways to check whether subsidence has ceased. Fix a piece of glass across a crack, using an epoxy-resin. Since glass has low tensile strength, any slight new movement will cause it to crack. You can bridge the gap with plaster of Paris. This will also crack if there is further subsidence.
All new structures settle and shrink and plaster cracks are not in themselves indication of subsidence.
Subsidence caused by building on clay may be apparent because cracks in inside walls may open and close with the weather. Serious settlement involves a costly and expert job of underpinning, in which hydraulic jacks may have to be employed.
Shrinkage may appear as stepped cracks in the brickwork joints, and sometimes even through the bricks. These can be repaired by raking out joints and repointing, or replacing cracked bricks.
Repairs should be carried out during dry weather, so that brickwork is dry, using a 1:2:9 mix of well-graded soft sand.
If it is difficult to point cracks you can feed a mortar grout into the fissures. Grout is a thinned mortar mixture.
The cracks should be masked with a plastic modelling or soft clay, or other impervious masking. The grout is poured into the fissure using a funnel and a piece of plastic tube. Allow the grout to dry out partially, and neatly point the crack surface.
Bricks can be repaired with mortar containing a pigment or a matching mortar made up with powdered brick of the same type.
10. November 2011 by admin
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