Stonehealth Doff being used to clean the Aviva building in York.
Being close to high levels of traffic pollution and next to water makes the Aviva building in York vulnerable to biological soiling.
Stonehealth DOFF was chosen (by Purple Rhino, which is a Stonehealth Rosette Approved Contractor) to clean the building because of DOFF’s ability to remove a variety of unwanted matter gently without causing any damage to the stonework.
The DOFF system is all about heat rather than pressure. The system produces 150°C at the nozzle with 30m of hose at a pressure similar to putting your thumb over the end of a hose-pipe, making it particularly gentle.
Pressure washers could remove biological matter but it would re-appear within six weeks. And the high pressures used would be likely to cause surface damage and remove even sound pointing.
Using pressure washers would normally be followed by a biocide wash. But it is well documented that biological matter builds up a resistance to the toxicity and then feeds off the residue, which has the outcome of even more biological matter than if the stone were left untreated.
The super-heated water of the DOFF system, on the other hand, not only renders it unnecessary to use chemicals but has the longest lasting effect of avoiding regrowth, with the high temperature killing off the spores that would lead to it. Test panel results also show a significant drying out of the cleaned area with DOFF, and biological matter cannot grow without water.
Stonehealth Stone Repair
Wind, rain, frost and atmospheric pollution cause physical damage to historic detail in stonework. Many historic monuments and buildings can benefit from having simple ‘plastic’ repairs and avoiding further damage without the need for complete replacement of masonry.
Many firms prepare ‘stone repair mortars’ bound with resin or cement but, based on Stonehealth’s site experience, this is not appropriate for most buildings, due to its hardness and lack of permeability.
Stonehealth has an alternative – a product that is highly vapour permeable and easy to apply and will achieve many different textures and colours, replicating even complex stone such as Yorkshire Grit.
This Stone Repair product sets quickly and can be dressed within eight hours. It produces a 100% natural mineral repair with a negligible shrinkage rate of 0.001%. This allows work to be scheduled even when there is a chance of frost.
Stonehealth Stone Repair has been used on many buildings and monuments in the UK, including: Spitbank Fort, Portsmouth; Grosvenor Hotel, Park Lane, London; Grade 1 Listed buildings by John Nash in Regents Park; and Bidestone War Memorial in Wiltshire.