PLGN 5.02 Brickwork & Stone - A Difficult Surface to Paint

Common Bricks are normally rendered or left unpainted, because of the high risk of failure due to poor adhesion of the applied paint film. Failure occurs over "kiss marks" in the bricks. Spalling is another problem that often occurs when the bricks become frosted.

Engineering Bricks are very hard bricks with low absorption to moisture. They are normally used for damp courses or for decorative heading bricks above windows and doors etc. They must not be painted because paint will not adhere to them and will quickly flake off.

Flettons are a common brick manufactured by the London Brick Company and named after the village near Peterborough where they are made. Flettons should not be painted externally for the reasons described above. The BRE publish a very informative paper 1P22179 Difficulties in Painting Fletton Bricks.

Glazed Bricks or vitrified bricks have a surface glaze which is melted on to the brick in the kiln during manufacture. They are normally used for decorative brickwork and must not be painted.

Stone is a durable material with an attractive natural appearance and, when new, does not require painting. Later in the life of a building, painting may be required to improve appearance, hide repairs, reduce rain penetration, etc.

Where external stone work is subjected to severe weathering conditions such as parapets, retaining walls etc, it becomes difficult to prevent the ingress of moisture. This can lead to the disruption of the paint coating . It is therefore not advisable to paint in these situations.

The types of natural stone to be found are numerous, varying in porosity hardness . Limestone and sandstone are porous whilst marble and granite are virtually non-porous. Stone is dressed in many different ways, thus affecting the surface texture. The successful adhesion of conventional paint systems will be affected by finish, texture, porosity, etc. For example, adhesion to a polished, non-porous stone is likely to be poor.

For further information on the painting of stone refer to B.S. 6150 : 1991: 33.2 (or as amended)