Researchers test WGL's new stone-cleaning technique

Researchers from Leeds University have shown that an alternative method of industrial cleaning, using diluted acid and super-heated steam, can be used safely on the ancient stonework.

Now, the so-called ’Steamacc process’ technique is being offered by WGL Stoneclean, a stone-cleaning company in the north of England.

The process involves spraying blackened stonework with a solution of dilute acid and then washing the surface with a high-pressure jet of super-heated steam at 150^oC. The acid essentially opens up the surface of the stone, allowing the steam to penetrate between and behind individual sub-millimetre-sized grains. Deposits of soot and dirt are then forced out by the power of the high-pressure wash.

The traditional method of cleaning stonework by shot-blasting the surface with sand, grit or chalk is effective but, owing to its abrasive nature, can damage the stone grains.

WGL Stoneclean asked civil engineers from Leeds University to analyse the surface of stone samples before and after Steamacc cleaning with three different strengths of the dilute acid wash. The researchers used conventional optical microscopy and a high-resolution scanning electron microscope (SEM) to look at samples of Yorkshire stone removed from buildings and a further set of samples prepared in the laboratory.