Civil Engineering Reference
In-Depth Information
water, the bonding characteristics and the permeability to moisture vapour
are particularly relevant properties - and the supplier's recommendations
should always be observed. Coatings are available for application to very wet
surfaces, even under water. However, this capability is formulation dependent
rather than being typical of a generic type. For the adequate absorption of
penetrants and sealers, water-free pores/capillaries are obviously essential.
The most appropriate method of application depends on the product type/
viscosity, the area to be treated and its continuity/accessibility. Common
methods are:
• Spraying
• Rolling
• Brushing
• Floodcoating.
Airless spraying, which utilises a high-pressure pump to atomise the
material, is most suitable for the rapid application of relatively low viscosity
products to unobstructed large areas. Air-spraying is suited to more
viscous products that are difficult to atomise - in this case, masking of the
surroundings is likely to be necessary, due to the overspray mist that is
created. Both methods become difficult to use in windy conditions.
Air-assisted spraying, using plant similar to that employed for 'guniting',
can place very thick products containing significant amounts of sand,
large filler particles or fibres. A finishing operation, typically trowelling, is
required and wastage, due to rebound, is inevitable.
Application by roller is commonly used for areas of intermediate size,
i.e. those that are too small/large for spraying/brushing, respectively. Brush
application is most suited to relatively small and/or inaccessible areas, and to
products, usually primers, that must be worked vigorously into the surface.
Flood coating is a technique that utilises a low-pressure spray to saturate
a surface uniformly with very low viscosity penetrants, particularly silanes/
siloxanes. A free-running wet front is maintained, working from top to
bottom on a vertical surface. A related technique, used on floors, employs a
'squeegee' to apply and spread flood coatings of penetrating sealers.
The range of ambient temperature and humidity that is acceptable during
application and drying/curing varies, according to both generic type and
formulation, and recommendations should always be available from the
supplier. In general, it is good practice to store materials in a controlled
temperature environment for at least 24 hours before use.
Particular care is required when temperatures are 'low and falling'
as condensation can affect both adhesion and appearance. It can become
essential to monitor ambient conditions and surface temperature to ensure
that application is not carried out in proximity to the dew point.
For reactive coatings, epoxies in particular, the recommended maximum
period between successive coats must be observed (with allowance being
