Comparison of CO₂, Nd:YAG and high power diode lasers for the ablation of tile grout

Process feasibility of a laser-based grout removal process and the effects thereof on the processing parameters have been successfully examined using three different lasers: CO₂ , Nd:YAG and HPDL (high power diode laser). The grout removal rate was found to increase linearly with laser power level. In contrast, it was affected very little by laser traverse speed. The optimum removal rate was obtained with the CO₂ laser and this occurrence was believed to be due to the CO₂ laser's wavelength. Surface morphological and material characterisation on the laser-removed grout was carried out. Depending on the laser used, colour ranged from white to dark grey. Significant differences between the untreated and laser-treated samples, as well as between the samples treated by the different lasers, were observed. The CO₂ laser produced relatively larger sized particles, with the Nd:YAG and HPDL generating finer particles exhibiting a similar appearance. An energy depressive X-ray (EDX) and an X-ray diffraction analysis (XRD) of the epoxy grout chemical composition before and after the laser treatment revealed that CaCO₃ (limestone) was decomposed to give CaO and CO₂ during laser interaction. The existence of SiO₂ , Ti and dolomite was also found in the original grout material. thermogravimetric and differential thermal analysis (TG-DTA) identified a sequence of three stages in the thermal history of the epoxy grout.