A floor made of concrete reinforced with steel or organic or mineral fibres is highly durable and can cope with both water and chemicals. On the other hand, it is less pleasant to walk on because it is hard and cold. This can be compensated for to a certain degree by adding sawdust, crumbled cork or light expanded clay. A concrete floor can produce a lot of dust through wear and tear unless it is treated with a waterglass solution, oiled, painted with a robust paint or covered by a strong floor covering. If the floor is to be covered with a watertight material, the concrete must be completely dried out before the floor finish is laid, otherwise humidity in the concrete will be trapped inside the construction. This can also lead to an alkaline reaction in the product with possible detrimental emissions to the indoor air. Complete curing of the concrete is best guaranteed if it is well-watered in the period after the concrete work. Gypsum and anhydrite are alternative floor materials with short drying times. They require covering with a strong surface layer. They can sometimes contain polyvinyl-acetate or melamin-urea-formaldehyde adhesives. The class of self-levelling mortars commonly consists of Portland cement, lime and fine sand with synthetic polymers added. The proportion of polymers can be reduced by adding a microfiller of recycled glass.
Terrazzo concrete causes less dust problems than a plain concrete floor, and offers a hard, hygienic surface. A terrazzo floor is a mixture of cement mortar and special chips of crushed hard stone of only a few millimetres in diameter, normally marble or limestone (Figure 15.1). Granite, feldspar or quartz can be used too. The floor is cast in a 15— 20 mm-thick layer on top of a concrete underlayer, and the surface is polished to a smooth finish by machine.
Both concrete and terrazzo floor materials are often prefabricated as tiles. These are usually 30 x 30 cm or 40 x 40 cm with a thickness of 4-6 cm.
Concrete floors represent considerable energy use and climate gas emissions during cement production. This is reduced where the cement content is lower. Various additives can also imply production related pollution.
On condition that concrete products are properly cured and treated against dust, they are chemically stable and pose no problems in the finished house. However, steel reinforcement can increase the electromagnetic field in the building.
Concrete and terrazzo tiles can be re-used if they are bedded in a way that makes them easy to remove. They can, for example, be laid in sand and given a weak lime cement mortar joint. Concrete floors cast in situ can at best be broken up and recycled as low quality aggregate or fill.
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