Civil Engineering Reference
In-Depth Information
Chapter 9.4
Paints and other liquid or
plastic finishes
information, see BRE Digest 197
(251)
.
Characteristic details
Basic structure
Systems for masonry
Whitewash, prepared from quicklime
and tallow with just sufficient water
to slake the lime and reduce the mix
to the consistency of pouring cream,
was the old recipe.
It depends on the availability of
quicklime to melt the 10% by weight
tallow content. However, treated
surfaces need yearly replacement.
Stuccos were normally painted
with oil bound formulations (Figure
9.31) and should not be overcoated
with water based formulations.
By the late 1950s, paint systems
for use on masonry were normally
one of three kinds:
●
cement-based mixtures which
might also contain other additives
such as lime, pigments or
accelerators in a water base
●
oil or resin-bound emulsions (also
in a water base) some of which
contained mineral fillers
Water repellents
Colourless, or nearly colourless,
liquids designed to increase the
ability of masonry to resist driving
rain have been available for many
years. They must be chosen with care
- see the later section on durability.
Water repellents are
distinguishably different from
waterproofing treatments to walls.
The latter provide a thin impervious
film to block the pores of masonry
and prevent all entry of water,
rendering the surface impermeable
Figure 9.30
Premature breakdown of maintenance
coats due to failure to adequately prepare
existing degraded paint and weathered
wood
This chapter deals with all kinds of
paints and other liquids used
externally on all kinds of surfaces,
and also covers building sealants
used externally.
Paints used externally on walls of
stone go back to medieval times,
when it was common for the stone
walls of better class houses and
castles to be whitewashed
(14)
. No
doubt also the cob or daub used on
more humble dwellings received a
similar treatment. Other pigmented
finishes were also used (Figure 0.66).
There is now a very wide range of
liquid finishes for all kinds of
materials, from water-shedding
virtually invisible coatings, to
stabilisers for friable surfaces and
highly decorative smooth or textured
paints; indeed, sufficiently wide a
range to meet virtually any need
except infinite durability.
Unfortunately, failures are still
relatively common (Figure 9.30).
conventional oil or acrylic paints
in a solvent base
●
Since then there have been
significant advances in the
development of suitable
formulations, though most still
resemble the earlier paints to some
degree, with the main development
being the increasing use of
solventless formulations.
Concretes may need to be painted
to reduce the progression of
carbonation. Even old surfaces may
still be sufficiently alkaline to
destroy the paint, and formulations
such as chlorinated rubber might
have to be specified. For further
Figure 9.31
Painted stucco - a traditional technique
with a fairly good track record
