Issue 37 Spring 23 WEB - Flipbook - Page 16
swirling vortex using a mixture of low air pressure, low
volume of water and a safe, inert fine granulate, which is
typically crushed marble. There are different aggregates
that can be used varying from very fine to coarse depending on the type of cleaning required. The most commonly
used type is calcite which is a fine grain. This cleaning
system is not suitable for use on all surfaces such as
faience as the aggregates are too abrasive for the delicate
glazed material.
residues is really important follow any chemical cleaning
procedure. Traditionally poultices were used on small,
localised areas of facades, but spray applied poultices have
been developed which are more cost effective and useful
for larger areas. Poultices can also be used in conjunction
with other water cleaning methods, as described above,
to soften deep-seated contaminants first.
When working with any water cleaning system it is vitally
important to ensure the minimum amount of water is
used to protect the stone. Despite this there will invariably
be water run off and a catchment system should or can
be used. Typically the water is captured in a catchment
system and removed via a puddle pump to the local water
way. Before passing into the local water way, the water is
filtered with the use of a fine gauze to remove any resulting sediment. When cleaning with chemicals the process
is slightly different. The run-off water is captured in a
catchment system and passed from here to a neutralization tank via a puddle pump. Dependent on the chemical
that has been used, a suitable neutralizer is then added to
reduce the chemical concentration to an acceptable PH
level before discharging into the water way. If an acceptable level is not achieved the resulting fluid is removed
via a certified hazardous waste carrier.
In some cases the above systems are not adequate and it
may be necessary to use poultices. These might be used
to remove various types of water-insoluble surface
contaminants such as paint and grease, soluble salts,
insoluble contaminants and metallic staining from porous
masonry surfaces. At Camden Town Hall, in addition to
the external cleaning and restoration package, extensive
interior cleaning and repair was also delivered. Part of this
included the badly soiled marble flooring and wall
cladding. This was initially hand cleaned with detergent
and water, before poultices were used on heavily soiled
areas. Poultice formats vary but can consist of a medium
that contains water or alkaline based cleaning agents.
Surfaces are pre-wetted to minimise penetration of the
cleaning solution into the masonry surface and covered
with plastic film to prevent the poultice drying out. At
Camden the poultice was left in situ for between 12-24
hours before the film was removed and the poultice then
allowed to dry for 2-4 hours. Following this the poultice
was removed, the area thoroughly washed and the marble
hand polished with a soft, dry cloth. The process of neutralising with clean water to remove potentially damaging
There really is no greater adage than “less is more” when
it comes to cleaning approaches to heritage and fragile
buildings, and there is no better example of this than a
skilfully cleaned and restored building.
www.szerelmey.com.
Below, Camden Town Hall after cleaning
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Conservation & Heritage Journal
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