A microbalance technique for the real-time measurement of carbonation in cement and lime pastes and mortars is described. Experimental results showing carbonation rates in a range of these materials are presented. The results confirm that the progression of carbonation is proportional to t1/2. Systematic differences in carbonation rate with hydraulicity are shown for a range of lime pastes of the same mix proportion. For lime mortars, the carbonation rate is shown to decrease as the sand particle size is increased for mixes of a given volume fraction sand content. Scanning electron microscopy shows the typical crystal morphologies produced on carbonation. It is shown that the microbalance provides a highly sensitive technique for the investigation of carbonation in cementitious materials.