This work provides detailed information on the surface morphology, microstructure and thermohistory of the epoxy tile grout resulfing from high power diode laser (HPDL) treatment using compressed air, Ar, N-2 and O-2. O-2 was found to effect the greatest removal rate, with the amount of removal with O-2 being up to twice as much as that with the other three gases. Such an occurrence is believed to be due to the fact that of the four gases used, O-2 is the most reactive, Microstructural analysis revealed differences in the grout surface structure before and after the laser treatment. The Surface of the laser-treated samples had a collection of grouped particles with pores and gaps, whereas the untreated sample had a continuous mono-structured plane surface. Larger sized particles were observed with O-2 gas compared to compressed air, Ar and N-2. Both an EDX (energy-dispersive X-ray) and an XRD (X-ray diffraction) analyses showed changes in chemical composition before and after the laser treatment. CaO and CO2 found in the laser-treated sample were considered to be the product of decomposition of CaCO3 (limestone). A TG-DTA (thermogravimetric and differential thermal analysis) identified a sequence of thermal history for the epoxy grout in which reactions in the laser interaction can now be predicted. (C) 2002 Elsevier Science B.V. All rights reserved.