The founder of stone conservation and restoration pioneers Stonehealth has warned specifiers and building owners of the risk of using inferior machinery and unqualified practitioners.

Brian Crowe said that since the latest iteration of the iconic Doff III machine launched earlier this year, increasing numbers of reports were coming in of impostor and incorrect machinery being used on sensitive restoration projects.

Instances included chemical damage to stonework, excessive pressure blowing out sensitive lime mortar joints and stripping of surface layers of masonry.

The company has even discovered a photo showing a competitor machine being used on a project in Scotland while carrying a Doff sticker in an attempt to appear authentic.

Such deceitful activity could lead to legal action either from specifiers or from Stonehealth.

“For the past 30 years we have created a reputation as the leaders in our field,” said Mr Crowe. “So while in a way it’s a compliment to have impostors pretending to be us, it’s not one that we welcome.

“What we are often finding is that our products are specified for projects but then, to save costs, inferior machinery is used by unqualified personnel.

“Our unique system enables high temperature steam – 150 degrees C at the nozzle end – to be gently applied when cleaning masonry. Any reduction in temperature must be compensated for by increased pressure, which is where damage can occur.

“One of our other products, the Torc, is able to carefully use granulate and a gentle swirling vortex to clean delicate masonry. Inferior products will result in damage to the surface.

“While this is a serious issue for our business – we risk suffering damage to our brand – we have a major concern about the impact of our heritage buildings.

“If damage is done, it’s irreversible. If you remove the surface of stone or break then you can’t get it back. If there are any doubts over the credibility of machinery and operatives, then contact us.”

Mr Crowe, who founded Gloucestershire-based Stonehealth in 1989, said education was key to ensuring that buildings continued to be properly treated.

“Our intention is to make architects, surveyors and other specifiers – including conservation officers – aware of people working with something different to what’s been specified or approved. Any queries on whether the contractors and machines are genuine should be directed to us. We know where our machines are and the personnel who are trained to use them.

“We place great emphasis on training the contractors who use our equipment, as well as ensuring that our machines are properly specified.

“Our reputation has been earned over decades of innovation and care for our industry and we won’t tolerate abuse of it, or the risk of unsatisfactory results from impostors harming the likelihood of our products being specified again.”

To help ensure that only bona fide contractors are considered and awarded contracts, Stonehealth has set up its Approved Rosette Contractors Scheme.

Approved contractors must meet stringent criteria including: full training in use of Stonehealth equipment, reviewed every year; use of only genuine Stonehealth parts and materials; annual inspection and servicing of machinery by Stonehealth; provision of at least two customer testimonials per year to maintain Rosette status.

Stonehealth is based in Cam near Dursley in Gloucestershire and supplies systems and products throughout the UK and many countries worldwide.