This paper describes a study to evaluate the effect of finely ground waste glass on the mechanical, chemical and structural properties of a NHL 3·5 hydraulic lime mortar. Finely ground waste glass was mixed with a natural hydraulic lime of classification 3·5 in the lime/glass ratio, 10: 1, 1:1, 1:2 and 1:3. Cylindrical samples were formed and placed in a controlled environment for up to 11 weeks. The mechanical properties were investigated by destructively testing the samples in compression before chemical analysis using Raman spectroscopy, energy dispersive X-ray spectroscopy and powder X-ray diffraction. The structure of the samples was investigated using focused ion beam microscopy. Evidence for a pozzolanic reaction at the glass /lime interface was observed together with the chemical process involved.