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 matter.

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 available.

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 applications

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.