The use of Knoop indentation for the assessment of the elastic properties of mortars and natural stones

•Reasonably good values of E can be obtained from Knoop indentation tests.•Heavy loads create subsurface fragmentation phenomena that alter the values of E.•Very small loads create inappropriately small imprints to be measured.•It is proved that elasticity parameter α=0.45 makes the results close to actual values.•Surface preparation of very porous materials must be further investigated.