MSc in Historic Conservation – Lime Day 2026

An annual highlight of the Oxford Brookes MSc Historic Conservation is ‘Lime Day’, where students undertake an extended practical skills workshop with building crafts specialists Owlsworth. The use of lime – that is, of limestone-based mortars, plasters and renders – was at the heart of building construction until the 20th century, and its replacement by hard, impermeable modern cement has done untold harm to historic buildings. During the workshop students gain experience of mixing and applying traditional building limes, as well as of working with other historic materials such as stone and timber. These skills take years to perfect, of course; but even a day’s experience, guided by seasoned practitioners, yields a better appreciation of the craft than any lecture could achieve. It’s also good, messy fun. 

Traditional mortars and plasters are made using quicklime, a highly reactive compound produced by burning limestone in a kiln; here the quicklime is being slaked with water to produce a basic lime putty, to which aggregates or fibres can then be added.

An alternative technique involves hot mixing, where mortar is produced by directly combining quicklime with wet sand.

Students also look at timber construction, including the varieties of structural timber and the range of methods for converting a tree-trunk into a set of building components.

Walling panels in timber-framed buildings were formed of wattle and daub, comprising a thick layer of fibre-rich mud applied over a woven lattice of hazel strips. Here, the daub is being mixed by adding straw to wet clay to increase cohesiveness.

Applying the daub

Once it has dried, the daub must be weatherproofed with a thin layer of lime-based render

External render can also be applied in the form of harling, a wet mix of lime and gravel that is flung against the wall

Finally, students try their hand at stone carving – here by trying to replicate the complex moulding profiles of a window mullion

Thanks to David Garrard for the report and the photos. To find out more about the MSc Historic Conservation, look here.