Stone cleaning
Minerva
has developed many different techniques for the sensitive removal of surface
pollutants. Buildings that are cleaned without proper care can store up
problems for the future. An example is this entrance porch that was saturation-cleaned
by water booms that were left on for long periods. This method, commonly
used in Bath and Bristol, leaves the structure too clean; removing the
patina of age and, more worryingly, blooming caused by the mobilization
of soluble salts, especially around the stone joints, which will lead
to rapid decay of the stonework.
All projects are different and no dogmatic rules apply but we prefer to
the use of a range of techniques including poulticing and timed, intermittent
mist sprays. For larger jobs we find the best way to clean materials such
as terracotta, Bath stone, brick and even wood is conservatively with the
Jos/Torc system.
When cleaning brick, for example, the fireskin is easily
damaged and once damaged the decay of brickwork can be rapid,. The JOS
cleaning system ischemical-free, gentle, efficient and causes no damage
to the material surface.
The JOS technique works with a mixture of water (up to 10 gallons per
hour), low air pressure and fine, inert abrasive powder. Together these
form a swirling vortex, which when fired onto the contaminated surface,
removes the the unwanted elements such as grafitti, certain types of paints,
carbon deposits, dirt and scale from a wide variety of materials. A range
of JOS nozzles are available for most tasks. The standard nozzle will quickly
and efficiently clean most surfaces. A micro nozzle can be used for more
detailed work and when matched with a soft abrasive powder such as talc
will not harm the surface.
The JOS system is chemical free and environmentally friendly,
which makes it safe and ideal for city centre use.
Another method of cleaning that we employ is the DOFF System of 'SuperHeated
Water'
The DOFF system is very different in action than other 'steam' or
'hot water' systems currently available and should not be confused with
them, as it is actually 'superheated' water that exits the heat-rsistant
nozzle, not just hot (70-90), or steam. The desired pressure can be adjusted
by the operator and is independent of temperature settings while within
the heater unit, the temperature can be increased at anything up to 150c
if necessary. The Doff is not suitable for old limewashes, delicate or
parlous stonework but can be particularly useful for the removal of oil-based
paints and emulsions.