Civil Engineering Reference
In-Depth Information
Renders create a finished surface which often does not need further treat-
ment. This is especially the case with lime renders, which can be given a matt
or polished finish. The treatment of walls with render also dates back thou-
sands of years. As well as its function as a surface treatment, render can also be
considered a climatic material, as it can provide wind-proofing and moisture
control.
The most common surface materials have rich reserves. Their common factor
is that extraction of the raw materials entails heavy defacing of the environment,
which can lead to changed water table levels or damage to biotopes.
These products usually present no problems in the indoor climate. The use of
certain additives can incur a risk of unhealthy dust and fumes. If steel reinforce-
ment is used, the electromagnetic fields in a building can increase. Many prod-
ucts can be re-used if they are easy to dismantle. They are usually inert and can
be used as fill. Additives, such as metal colouring agents, can cause pollution
when dumped.
Roofing materials
There are two types of concrete roofing: tiles and corrugated sheeting. Certain
amounts of fibre must be added to give it the required tensile strength. The low
weight of the sheeting makes it possible to produce it in a large format. More
than any other concrete product, roofing needs particular care given to the pro-
portions of the ingredients and the design of the sheeting or tile. One very
important aspect is that the concrete used must have very low moisture absorp-
tion.
Concrete tiles and sheeting are usually made of Portland cement, but other
hydraulic cements can also be used. The added fibres can be chosen from
organic materials such as hemp, sisal, jute, reed, goat hair and cellulose, and
from fibres of minerals such as silicate, steel, carbon, asbestos or mineral wool.
Organic fibres are more easily decomposed. Research has proved that even
when organic fibres have decomposed the sheeting has the same strength
(Parry, 1981). The reason for this is partly that the fibres play their most impor-
tant role during the setting process - it is during this period that the dangers
of damage through shrinkage are greatest. Organic fibres used in concrete
must be resistant to attack from lime. They also have to be free from any chem-
icals that can break down the cement. They can be treated the same as in
woodwool slabs (see 'Woodwool cement boards - production and use',
p. 284). It is also important that the fibres are easy to mix and bind easily with
the mixture.
Roof sheeting was originally produced mainly with asbestos fibre, but this has
now been replaced by cellulose fibre for health reasons, in a proportion of two
