Laser cleans, client beams
June 1st 2008

Cleaning fragile environments can be a tricky task but using lasers provides a fast, effective solution. Tube Tech blitzed years worth of grime on the fragile stonework of a Grade 1 listed museum building in record time with its laser technology

Removing over 140 years worth of grime from any building would be a challenge to most cleaning contractors.Add the fact that the building is Grade 1 listed, closely monitored by both English Heritage and the Victorian Society, and the job presents the kind of challenge that Tube Tech International says it loves to take on.

The building, a town museum, was significant in the development of 19th century architecture, the history of its university, and in the study of science in England.The museum is visited by over 300,000 people per year.Visitors plus other environmental pollutants had caused a build up of dirt on the viewing galleries stone work.The building's administrators wanted the stone work cleaned back to its natural state, with the area to be cleaned including the walls and columns of two 40m galleries.Due to funding restrictions, the time frame for the work to be completed was 12 days.

Working conditions The stone work was fragile – some areas could be marked with the scratch of a fingernail – so protecting it was crucial.Other surfaces which the contractor might come into contact with, including the highly detailed tiled floor, also had to be protected. In addition, the work had to be completed during the building's traditional opening hours, and as the building would continue to be open to the public, priceless exhibits would be displayed in the area directly below and around the cleaning operation.

Previously the museum's maintenance team had spent three years with hot water and a brush cleaning one side of the gallery's stone work.The museum had also used a laser cleaning contractor, utilising two laser systems, eight hours per day, seven days a week, who took in excess of three months to clean two 40m sections of the gallery.

Due to the museum's time restrictions,Tube Tech used a 50 and 70mm laser which is far larger than traditional laser cleaning equipment.This meant that a small team could clean a larger area much more quickly.Aware of safety issues,Tube Tech ensured that no member of the public was able to look directly at the laser as this could have damaged their vision.

Lasers have been successfully used across the world to clean monuments while preserving patina, fine surface details and important surface coatings. Laser cleaning works by ablation: the coating layer is removed as it absorbs the focused laser line.Very powerful but short laser pulses have little thermal influence on the base material.The blank base material reflects laser radiation, stopping the ablation process.With the 'correct' laser parameter and 'best'wavelength, the profile of the stone cannot be damaged and the dirt removed is vapourised (ablation by sublimation) and removed by thermally-induced pressure.

Tube Tech also used its specialist access scaffold tower which features a cantilever, enabling work on the front leading edge.The Tube Tech team ensured that rubber matting was used underneath the laser equipment in order to protect the delicate tiled floor of the museum.

Tube Tech cleaned a full 40m gallery in 10 days (which the company believes is almost four times faster than previous laser technology) and it met the safety, security, conservation and protection issues as specified by the client.

"Working on a cleaning contract surrounded by priceless exhibits was a first for our team, and seeing the difference on the stone work after the laser cleaning was highly satisfying," says Eamonn O'Connor, Tube Tech sales engineer."The use of our larger laser within this fragile environment was a perfect choice as there was no noise emission.The vaporised waste was vacuumed away immediately and there was no interruption to the museum's activities."