This section deals primarily with the application of surface coatings to common brickwork.
Common brick protection
The most commonly applied finish on common brickwork is plaster and paint. It is in our experience, the only truly durable finish for this type of brickwork.
Bag wash and paint
This form of treatment to common brickwork is popular because of its first cost. It is, however, not a durable finish for many reasons, not the least of which is its lack of good mechanical strength. Bag washes fail through flaking and peeling and generally do not have a life of more than about three to five years on the external faces of walls. As an internal finish, bag wash and paint is of course far more durable.
It is important at the point of application of the bag wash, during construction, to take account of the ‘pot life’ of the materials. If the initial set of the cement takes place prior to the application of the bag wash to the wall, its mechanical strength and hence durability will be considerably reduced. Further, freshly applied bag wash will dry out quickly on walls exposed to the sun and unless it is wetted down during the initial setting period of the cement, the mechanical strength of the bag wash will be reduced.
PVA paint on brickwork
PVA paint applied directly to clay brickwork is not recommended as it does not key well. Moisture movement through the wall causes the paint skin to peel.
SURFACE DRESSINGS ON FACE BRICKWORK
Varnish and brick dressings
Varnish and brick dressing suffer from poor key and rapid deterioration due to sunlight and moisture movement. These finishes are difficult to remove from brickwork and so it is almost impossible to restore the wall to its original condition.
Oiling of brickwork
If it is desired to brighten up brickwork, a mixture of clean engine oil and paraffin in the ratio 1:2 is recommended. This application gives a characteristic “oiled” appearance, without harmful side effects. The finish is not durable, but because it disappears through evaporation, can readily be re-applied without any further cleaning or pre-treatment of the brickwork being required.
The use of silicones on brickwork
Silicones are primarily water repellents and such can be used to assist in the solution to rain penetration problems. The application of silicone to brickwork, however, will not upgrade the durability of the product and is therefore, not a solution to problems arising from the incorrect application of bricks.
Silicones act by preventing water entering the pore structure of bricks and mortar through a water repelling action and not by a clogging or sealing of the pore structure. Silicone application does not prevent moisture movement through the wall, as water can still evaporate through the pore structure. Water penetration through cracks in bricks or mortar will, however, not necessarily be prevented by the action of silicone.
Research has been carried out into the possible use of silicones as a means of improving the rain penetration resistance of brick and block waling. Although the effectiveness of this treatment has now been proven, there is a lack of South African based scientific information regarding the durability of such finishes. To assist in finding an answer to this question, a blockwork test panel was set up at the National Building Research Institute in Pretoria. This panel, when tested for rain penetration in accordance with the standard test set down in the national Building Regulations, displayed significant water penetration. The test panel was subsequently allowed to dry out and then carefully siliconed. On re-test the wall showed no signs of water penetration. By agreement with the NBRI, this panel will be retested for rain penetration resistance on a six monthly basis.
In Europe, silicone durability has been assessed at least 15 years. The presence of a greater proportion of ultra-violet light in sunlight in South Africa, however, is likely to shorten this life. As and when the results of this research become available, the technical data will be updated.