Hirst Conservation offers a variety of
specialist cleaning processes for the removal of dirt,
pollution, graffiti, surface fire damage or
inappropriate modern paint systems from historic fabric.
Expertise in multiple aspects of building conservation
and technical analysis enables Hirst Conservation to
provide a complete and professional service for the
cleaning of historic buildings.
The main processes used by Hirst
Conservation for the cleaning of building facades are
the JOS, DOFF and KRAKE systems.
Other systems employed for the cleaning
of building surfaces include steam tools. latex,
chemicals, reagents, micro-air abrasive techniques,
laser cleaning and poulticing. Prior to commencement,
the most appropriate cleaning method is identified
through discrete tests.
The JOS system
JOS is essentially a wet, mild jet
abrasive cleaning system, made suitable for conservation
applications by a controllable low pressure vortex of
air, water and granulate, swirling almost parallel to
the surface of the stone. The swirling action cleans
away unwanted matter more carefully than conventional
right-angle impact systems.
JOS is chemical-free and environmentally
friendly system, in which dust and slurry levels are
kept to an absolute minimum. It is gentle enough to be
used on delicate surfaces, including mouldings and areas
of carving. Experience has shown that this system is
unsurpassed in its efficiency in removing black sulphate
skin from limestone.
The DOFF system
A normal water supply is taken into a
high pressure pump, and the pressure increased to the
appropriate level before it enters the hot-box where, if
necessary, the temperature is increased up to a level of
150°C. This is then fed through high pressure heat
resistant hoses to the nozzle. Special jets, efficiently
directed to the surface, cut through and remove unwanted
The ability to maintain high
temperatures and low pressure is a particularly special
feature of the DOFF system. However, simultaneous high
pressure and high temperature can be introduced if
necessary for the removal of paint and other heavy
coatings. Heating of the surface is controlled and dry
within minutes. Depending upon the requirements of the
system, a range of appropriate lances and nozzles are
The KRAKE system
The Krake system uses either the high
pressure hot or cold water spray system of the Doff or
the mild abrasive system of the Jos. It has the
advantage of removing the water debris at source by
vacuum, thus preventing any water run-off down the walls
or into the building fabric.
Please contact us for advice on specific
Some of our projects include:
St Michael and All Angels Church,
Newburn – Cleaning, repair and conservation of
entire interior including fittings following a fire.
Peterborough Cathedral –
Removal of graffiti from external stonework
The Grotto, Stowe School –
Surface cleaning of internal and external finishes,
including various mineral dressings/ornamentation
St Ambrose Church, Bournemouth
– Complete restoration of a fire damaged church
Bishop’s Gatehouse, Norwich –
Cleaning of façade
Uppark House (National Trust)
- Consultant for interior decoration and supply of
bespoke pre-aged lead paint.
Windsor Castle - Conservation
of fire damaged stonework and other works.
St Pancras Chambers, London –
Conservation of fire damaged stonework
St Clements Church, Ipswich -
Complete restoration of fire damaged church.