Many Building Materials such as Brick and Tile contain Clay and Sand as the main Materials.
A Sydney Building Defect Report might comment on a common building defect refered to as ‘Fretting’. Fretting is a form of deterioration commonly found in clay based terracotta / ceramic building products such as bricks and roof tiles, especially in older style properties or in coastal locations.
Before we explain Fretting, it is important to keep in mind, the typical domestic house brick was actually a natural clay material to begin with. The same goes for all ceramic building products such as roof tiles, floor tiles, pavers, some types of cladding as well as pots and other household ceramic items.
Clay based materials have been in use for at least ten thousands years, possibly much longer. The word Terracotta comes the Italian ‘terra kotta’ which literally translates to baked earth and from the Latin ‘terra cocta’ which means cooked earth.
Clay is still used for making modern house bricks. Most bricks are made by combining raw materials like clay, sand, shale and water. The materials are mixed, shaped (either by extrusion or dry pressing) and then baked / fired in a kiln at very high temperatures (1,000-1,200 degress). The baking process creates a series of chemical and physical changes in the material such as ‘sintering’ and then vitrification. Sintering in manufacturing is the process of turning powdered materials into a solid material through the application of heat and pressure. Vitrification occurs where the heat melts the sand into a ‘glassy’ liquid that fills the spaces between the particles. This firing process makes the bricks very durable to the weather and very strong in compressive strenght, yet relatively light and easy to mass produce.
Major brick fretting pier
Major tile fretting with hole
Mortar fretting in basement garage
Modern fully glazed roof tiles
Older Versions of these clay based Building Materials Suffered from a condition Known as "Fretting".
However earlier versions of these clay based building products sometimes suffered from deterioration known as fretting. Fretting is casued by the migration of mineral salts through the material. These minerals are ‘water born’, that is they are present as disolved minerals/salts in water. The exposure of brickwork or roof tiles to this mineral rich water allows the minerals to crystalise (to form crystals and come out of solution) in the microscopic gaps in the building material. Over a long period of time (usually many decades) the minerals or salt crystals build up causing surface damage or decay of the material, eventually causing failure of the element.
Areas we commonly find brick fretting include subfloor footings such as brick piers and lower subfloor walls in older style homes (30-40 years and older). This is due to the natural occurance of moisture in these low lying areas.
Around swimming pools is another common place to find brick fretting problems. This is due to the use of chemicals and mineral salts in the sterilisation of swimmings pools. Fretting is sometimes found on bricks or pavers around pools and pump houses.
Fretting of Terracotta roof tiles is common in very old buildings with unglazed and semi-glazed roof tiles (1920s-1950s) and also occurs with some more recent glazed roof tiles from around the 1970’s. Its not something we tend to see with modern fully glazed terracotta tiles. Roof tile fretting is ubiquitous in coastal locations due to the high salt content in the air which accelerates the fretting process.
Generally speaking repairs to fretting are not really possible and replacement of the affected materials is needed. In some instances it may be suitable to install a sealant or protective coating to help slow the process down.
Other things to think about include: Possible site drainage problems, Subfloor ventilation improvements as well as making sure the roof plumbing is clear and free flowing.
