Fat-Lime Mortars

Fat-lime (often called Non-Hydraulic or High Calcium) mortars and plasters set by a simple chemical reaction between lime (calcium hydroxide) and airborne carbon dioxide. Because of this characteristic, fat-lime mortars and plasters set slowly and need to be carefully cured and protected. Nevertheless, in return for this special care, these mortars and plasters are the most suitably flexible and forgiving to the vagaries of historic solid masonry structures. This type of lime, often indirectly produced during the once common process of ‘hot-lime’ mixing, has been found to be the almost universal binder in Irelands historic (pre-1850’s) mortars and plasters.

Almost as long as these mortars have been used, certain reactive materials, known as pozzolans, have been added to produce other chemical reactions, most often to induce a quicker set or increase durability. In more recent times, many other materials have been gauged with lime to induce a whole range of perceived benefits.

Fat lime mortars and plasters today are prepared with 3+ month old, highest quality lime putty carefully mixed with appropriate washed, sharp sands and aggregates. Ready-to-use mortars are available in 20L tubs or 1 tonne bags for on-site efficiency. A range of suitable Pozzolans are also available for mixing immediately prior to use.

Our Lime experts give practical advice on all lime-related matters. Please feel free to call us.