Diode Laser Removes and Seals Grout

Brent D. Johnson

To ease the removal and sealing of industrial grout for ceramic tile, Jonathan Lawrence of the School of Mechanical and Production Engineering at Nanyang Technological University and his colleagues at Manchester University's Institute of Science and Technology in the UK have developed a handheld laser device. On-site field trials of the system, which is nondestructive to the tiles, may begin this summer.

A dermatological laser is finding application in the removal and sealing of epoxy grout for ceramic tile. Courtesy of Jonathan Lawrence.

Ceramic tile is used in industrial applications because it is impervious to abrasion and chemical etching. However, the epoxy grout that cements the tiles has a limited lifetime and may become contaminated. For example, the tile used in nuclear processing as well as in the food processing and brewing industries is exposed to harsh solvents that degrade the grout, reducing its strength and wear resistance. Periodically, grout must be removed and exchanged, a labor-intensive job that involves a variety of tools that can damage the tile, such as diamond cutting blades, chisels, caustic chemicals and heat guns.

The new device consists of a small, portable housing containing a D60 diode laser from Diomed Ltd. of Cambridge, UK. The laser, which also is used in dermatological procedures to treat vascular and pigmented lesions, emits 810-nm radiation and operates in continuous-wave mode from 0 to 60 W.

Lawrence said that this was the least expensive and most powerful laser on the market at the time of purchase and that it demonstrates how useful such devices can be. "Indeed, the fact that the D60 laser we employed to perform an industrial task was originally designed for medical purposes goes a long way to support the idea that lasers are some of the most flexible tools around."

The laser light is delivered to the work area through a 4-m-long, 600-µm-core-diameter optical fiber, which is connected to a 2:1 focusing lens assembly. The laser spot heats the epoxy grout, and water evaporation, material expansion and decomposition of organic compounds in the target produce internal stresses and pressure within the material, ejecting it from the site.

The researchers calculated the maximum removal rate at 65.98 mm²/s for a circular 2-mm-diameter beam with a power density of 3 kW/cm² and a traverse speed of 42 mm/s. The same system can be used to seal new grout with a power density as low as 550 W/cm² and a travel rate of 420 mm/min.

Besides avoiding damage to tiles, the benefits of this technique are easy deployment, reliability and robustness. The only limitation to the use of the laser tool may be its price tag, Lawrence said.