Civil Engineering Reference
In-Depth Information
are based on binders of lime, cement and waterglass, all of which are soluble in
water.
The products are based on rich reserves. The environmental consequences of
the production techniques can be acceptable, e.g. when using water as a solvent.
All the alternatives are strongly alkaline and when damp have a corrosive effect
on bare skin. Compared with other working environments and indoor climates,
mineral products produce favourable results.
In buildings the products are environmentally sound, partly because they are
open to vapour transport and do not mask the moisture-regulating properties of
the materials underneath. An exception is lime or cement paint not well bound
to the surface, which can loosen and flake off into the room and cause respirato-
ry irritation. Mineral paints cannot cause electrostatic charging.
As waste the products are inert, and as long as there are no poisonous pig-
ments in the paint they can be used as fill. The paint will not lessen painted prod-
ucts potential for recycling, or for energy recycling.
Lime paint
In lime paint the binder is slaked lime which can be bought separately in tins.
Curing is based on carbonizing slaked lime with carbonic acid in air, forming a
united crystalline layer. The pure lime colours give matt, absorbent surfaces
which are difficult to wash. The paint is porous to vapour and not elastic. It binds
best to a lime render but can be used on pure cement or rough timber. Brick can
best be painted with lime if it has a rough surface. Lime paint cannot bind to plas-
tic. The best results are obtained by applying lime on fresh render. Old lime paint
can be removed by brushing.
It is important that lime paint is applied in thin coats. It can be used both inside
and out, but walls painted with lime paint cannot be painted over with any other
type of paint - the lime paint must be completely removed. It is important that
the pigments are compatible with lime. If the lime contains more than 5-10 per
cent additives, it has a lower binding capacity.
The following pigments are considered compatible with lime: titanium white,
yellow ochre, ferric oxide yellow, cadmium yellow, red ochre, ferric oxide red,
chrome red, ultramarine, cobalt blue, earth green, chrome oxide green, umber,
brown ochre, terra de sienna, ferric oxide black, ilmenite black, bone black.
Factory-manufactured lime paint has dolomite added to improve its durabili-
ty, plus a little sinew glue or cellulose paste to improve ease of application and
opacity. Water-soluble glue is eventually washed out.
Lime paint gets dirty easily in urban environments. It is very sensitive to acids,
which break it down to gypsum. It is therefore debatable whether this paint should
be used in an area with an acidic atmosphere. The surface underneath is, howev-
er, protected from acidic attack, and the lime acts as a sort of sacrificial layer.
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