In South Africa there are many low-rise, unreinforced, load-bearing masonry (ULM) buildings in seismic zones due to shortcomings in South Africa0s design codes. These buildings pose a great risk to their occupants in the case of seismic activity . A possible solution is to retrofit these buildings with a strain-hardening cement-based composite (SHCC) overlay. It is postulated that the strain hardening characteristic of the SHCC overlay may sufficiently increase the ductility of such buildings to prevent collapse during seismic activity. This paper discusses the effects SHCC have on the damaged behaviour of masonry walls under in-plane seismic action. These effects were evaluated using experimental pushover tests with different retrofitting techniques. From the tests, it was concluded that adding an SHCC overlay increased the in-plane shear resistance of a masonry wall. The ductility was improved by introducing debonding strips between the masonry wall and SHCC overlay. The SHCC retrofitting scheme was numerically optimised using non-linear finite element (FE) analyses. Masonry was modelled using a smeared crack model with a Rankine-Hill material to allow for tensile softening and compression hardening followed by softening as well as an Engineering-Masonry model to allow for multi-directional loading. The interface between the masonry wall and SHCC overlay was modelled using a Coulomb friction model. The SHCC overlay was modelled using a Rankine-Rankine model with compression and tension hardening.