Civil Engineering Reference
In-Depth Information
make the paint more matt. Important fillers are kaolin, dolomite, talcum, sand,
fossil meal, diabase, heavy spar, barite and calcite. In the original earth colours,
neutral clay silicates from the earth were used as natural fillers.
Fibre materials
Fibre can be added to paint to make it tougher and provide reinforcement on dif-
ficult surfaces.
Thickeners
Thickeners are added in water-based plastic paints to give the paint a slow flow-
ing consistency. Water-soluble cellulose glue or derivations of polyurethane and
polyacrylate are used for this.
PH-regulating agents
These can be added to water-based plastic paints to increase the pH value and
reduce the chance of mould growth. Ammonia or triethylamine are usually used.
'Skin preventers'
These are added to stop a skin forming on top of the paint in the tin. The sub-
stances used are buthyraldoxime and methylethylketoxime, added in propor-
tions of 0.1-0.4 per cent.
Rust preventing agents
These prevent rust being formed on the tin or when painting metal surfaces such
as nails, etc. Traditionally they contain chrome and lead compounds. In water-
based paints a mixture of sodium benzoate and sodium nitrite is used in pro-
portions of 10:1, and makes up around 0.5 per cent of the paint.
Fungicides
Fungicides are often necessary to prevent the paint from attack by mould during
storage and after application. The least toxic alternatives are lime, and metal sul-
phates such as alum and ferrous sulphate, which are used in many paints with
organic or even mineral binders. Some pigments also have preservative capaci-
ties. Paints with 50 per cent zinc white are not attacked by mould. Water-based
plastic paints often contain a fungicide of many different compounds, including
chloric-organic substances. Up to the end of the 1970s polychlorinated biphenyls
(PCBs) were used. In certain water-based plastic paints pentachlorophenol is
probably still being used. Other common fungicides are sodium nitrite,
formaldehyde, tributyltin and isothiazolone. Fungicides make up about 0.5-1.0
