Civil Engineering Reference
In-Depth Information
and gypsum products are good moisture-regulators. The use of a filling
between the sheets could result in emissions of monomers. The joints can also
be covered by a timber strip or the products can be tongued and grooved to
overcome the need for filling.
Products that do not have added filling can often be recycled. Pure plaster-
board (gypsum sheeting) is too weak to be dismantled and re-used as is, but the
material can be recycled as 5-15 per cent of new material. The gypsum industry
is, however, very centralized, which makes it economically non-viable to recycle
the products. Calcium silicate products can be crushed and recycled as aggregate
in concrete. If it is finely ground, it can be used in mortars and render. The waste
is inert and can be used as fill, as can pure mineral cement products. If there are
high levels of organic substances in the products, when they become waste they
may increase the amount of nutrients seeping into the groundwater. Sulphur pol-
lution can develop from waste plaster through decomposition by microbes; this
can be reduced by adding lime.
Render
There are several alternative renders, depending upon the surface to be ren-
dered, climate, elasticity, etc. The usual binders are lime, cement, gypsum and
sulphur or mixtures of these substances. Additives can make the render bind bet-
ter or improve elasticity or thermal insulation; they include steel fibres, mineral
fibres, perlite, hacked straw, or even hair from cows, pigs and horses. Pigments
can be added; these should be fine grained and calciferous, usually metallic
oxides. For external rendering or rendering in rooms such as bathrooms, water-
proofing agents called hydrophobic substances are added, such as silicone prod-
ucts. Sand is also added, its grain size depending upon the surface quality
required and how many layers of render are to be used. The final ingredient is
water.
Rendering is labour-intensive work, but as a result it has a long life span. Well-
applied lime rendering can last from 40 to 60 years, if it is not exposed to aggres-
sive air pollution. Organic substances added to increase waterproofing and make
application easier have a detrimental effect on the durability of the rendering.
The raw material availability of the different components of render is general-
ly good and the environmental aspects of production are also favourable, espe-
cially for lime rendering. Pure rendering produces no problems within a build-
ing. Lime- and gypsum-based products have good moisture-regulating proper-
ties. Pure lime render can be recycled, in theory, by being re-fired, but this is
impracticable in reality. Lime- and cement-based renders can be classified as
inert, so their waste products can be used as fill. Pure lime render can be ground
up and used to improve the soil. Dumping sulphur and gypsum waste can lead
to sulphur pollution, but this can be reduced by adding lime.
