Civil Engineering Reference
In-Depth Information
the 1950s and contains large quantities of solvent, usually aromates like toluene
and xylene. Alkyde oil paint with less pigment can also be called a stain. It does
not penetrate material as well as pure linseed oil paints, but it adheres well to
wood even if the surface is not completely dry. Alkyde oil paint is also consid-
ered hardwearing, and is used on concrete, render and galvanized iron. With no
pigment, the paint can be used as varnish.
Alkyde oil is very thick and because of its high percentage of solvent
(between 50-70 per cent), alkyde oil paint is a big risk in the working envi-
ronment. The emission of solvents in the building can continue from a few
days to several months, depending upon the climate of the room, how the
paint has been applied and the type of solvent. In certain alkyde oil products,
mainly the varnishes, alkylphenols are present in the binder in a proportion of
about 1 per cent by weight. Alkyl phenols are confirmed environmental
oestrogens.
Water-based synthetic resins
These resins are based on the dispersion principle where the plastic con-
stituents polyvinyl acetate (PVAC), vinyl acetate, polyacrylate or styrene acry-
late move freely about in the water in the form of microscopic plastic pellets.
To make the mixture work as a paint, additives such as pH-regulators, fungi-
cides and softeners are needed. Paint with polyvinyl acetate as a binder was
introduced early in the 1930s, and it is still used as a cheap interior paint.
Styrene acrylate is a sampolymer of polystyrene and acrylate and is used both
inside and outside. But the most common binding agent nowadays is poly-
acrylate. It is more expensive than PVAC products, but has a better resistance
to alkalis, better weather-proofing and adheres better to smooth surfaces.
Most of the water-based synthetic resin paints today contain a mixture of
polymer binders. Binders form about 30-40 per cent, pigment 30-35 per cent,
fillers 16-20 per cent, water 20-25 per cent and different additives about 5 per
cent. A homopolymer PVAC paint has to have softener added to make it suit-
able as a paint. If a co-polymer of PVAC and acrylate is made the necessary
softness will be achieved without having to use a softener. Most paints also
contain a small number of organic solvents to increase the possibility of form-
ing a film.
Water-based synthetic resins and emulsion products are matt. They are not
suited to surfaces that are exposed to damp, and often get thicker with age.
Acrylate monomers in water-based paint can cause eczema through contact
with the wet paint. Some paints emit ammonia when damp which is very irritat-
ing to the mucous membranes. Many of the water-based synthetic resins can emit
volatile compounds for long periods after painting is complete, such as excess
monomers of acrylates, styrene, softeners and volatile components of fungicides
such as formaldehyde, and even excess solvents. All of these can stimulate over-
