Fired Clay

Basic info is found in Chapter 8.

Fired clay products can be used for a wide selection of surface materials for roofs, walls and floors.

Roof tiles of fired clay were used very early in the history of the Mediterranean countries, the most popular being 'nun' and 'monk' tiles. In the mid-nineteenth century, the interlocking tile was first produced in France; compared to previous types, it provides better waterproofing and increased fire safety (Figure 15.3).

Roof tiles require high clay content and low lime content. Fired lime particles can easily absorb moisture in damp weather and destroy the tile. The tile is fired at a temperature approaching sintering, about 1000 °C, to reduce porosity. Roof tiles can be glazed and coloured, mainly for aesthetic reasons.

Clay brick veneering of inner and outer walls is usually done with ordinary construction bricks that are placed in mortar on concrete, steel or timber structures. A special version is the fired clay slab that can be produced in dimensions up to 60 x 180 cm with a thickness of 3-4 cm. It is usually mounted on special metal anchoring systems, with good ventilation behind. Brick products can also be used as flooring, laid on sand or in mortar.

Ceramic tiles are used on floors and walls. These are usually square or rectangular in form, but specially designed tiles of many other shapes (e.g. triangular, octagonal or oval) are also available. Tiles that are coloured right the way through are usually dry pressed and fired to sintering temperature. Many products have an additional glazing.

Fired clay products are based on raw materials found in abundance in most regions. Products destined for use as exterior cladding, roof covering, or untreated floor covering should have a very low porosity rate. As this entails firing at high temperatures, this necessitates a high

energy demand in the production process and large emissions of the greenhouse gas carbon dioxide, as fossil fuels are most often used. Lime cannot be added to reduce emissions of sulphur, as this would increase the porosity of the products. This is not a problem with brick veneers for inner walls; here, it is also possible to use low-fired products.

Fired clay products are excellent materials for indoor areas. They are hygienic, do not release gases or dust, and are usually good regulators of temperature and moisture, the latter only if they are not highly fired and sintered. Modern jointing materials for ceramic tiles usually have polymers such as epoxy and polyurethane as ingredients. These can give unhealthy emissions into an indoor environment. In Sweden, mastics with organic constituents have led to mould problems, especially in bathrooms. Pure mineral alternatives are better for both floors and walls.

Fired clay products are very durable. They are not susceptible to aggressive gases and pollution in the same way as concrete and natural stones containing lime. To take advantage of the material's durability, the products should be mounted or fixed in such a way that they will be easy to dismantle and recycle. Roof tiles are no problem to re-use, but it must be remembered that tiles in coastal climates have often been exposed to more frequent changes of temperature between freezing and thawing, making them more brittle. A brick floor laid in sand can be lifted and re-used. The same can be said for internal brick cladding that is laid in a lime mortar or clay. If a mortar rich in Portland cement is used, both careful dismantling of the wall as well as removing of the mortar afterwards is practically impossible.

When crushed, fired clay products can be recycled as aggregate for smaller concrete structures, render and mortars. Waste products from

15.5

Floor covering of brick in sand, which are easy to remove and re-use.

15.5

Floor covering of brick in sand, which are easy to remove and re-use.

plastics-based mortars for jointing and colouring containing heavy metals are problematic. In cases where antimony, nickel, chrome and cadmium compounds are included, special disposal is required. As long as no standardized coding exists for coloured ceramic tiles, all tiles must be treated as a dangerous waste product.

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