Schmidt hammer

When conducting the test, the hammer should be held at right angles to the surface, which in turn should be flat and smooth.

The rebound reading will be affected by the orientation of the hammer: when used oriented upward (for example, on the underside of a suspended slab), gravity will increase the rebound distance of the mass, and vice versa for a test conducted on a floor slab.

Twelve readings should be taken, dropping the highest and lowest, and then taking the average of the ten remaining.

This method of testing is classed as indirect as it does not give a direct measurement of the strength of the material.

It simply gives an indication based on surface properties, and as such is suitable only for making comparisons between samples.