Do not assume every mortar was created from a hot lime mix
We need to remember that within the current fashion for recreating hot lime mortars that in many areas historically the burnt lime was very difficult to use in such a way.
Just back from helping crafts people and specifiers in northern Ethiopia develop their skills and understanding of traditional plasters, Mark Womersley watched and worked with local people to prepare lime renders and plasters.
The burnt limestone currently used has a high iron content and when tested is naturally hydraulic but without the crushing equipment and the ability to slake using steam much of the burnt lime remains as large lumps of un-slaked material when water is added to it. Often two thirds of the content of each batch of quicklime has to be discarded as it remains un-slaked.
The slaked material runs into pits as a slurry and needs to be left for 6 months to 10 years to mature into a lime putty with sufficient concentration of calcium hydroxide within it to be affective as a binder.
The tradition in this part of Ethiopia at least in more recent times crushes by hand this waste material to make an aggregate, providing mixes of a very high lime content that give the appearance when set of a hot lime mix. But this is false.
These mixes provide a very good set over longer periods of time and have in recent years been used to create limecrete domes and waterproof swimming pool lining plaster. This area of Ethiopia receives up to 1 metre of rain fall per month in the wet season and the mortars are tested with this onslaught.
The mix appears to create a hydraulic mortar that gains strength over time and forms a very durable material.
Slaking lime into a pit
Specifiers learning from crafts people how to crush the unslaked lime to use as an aggregate
The early 17th Century Fasil Bath lined with lime rich feebly hydraulic plaster
A dome recreated with unslaked lime aggregate 30mm down and slaked lime from mature pits
Great that the press picked up on our work with the craftsmen in Barbados, and with local people
Great that the press picked up on our work with the craftsmen in Barbados, and with local people to …
On our last day in Barbados, it was good to see the vertical sliding sashes, made from Guyana Purple Heart wood, going back into frames within the Garrison House at Bridgetown. Tutors and students from the Samuel Jackman Prescod Institute of Technology, with a little support from Mark, copied adjacent windows to begin conservation work on this building.
On our last day in Barbados, it was good to see the vertical sliding sashes, made from Guyana Purple…
Mark was very pleased to help Grantley Adams Memorial School, and a voluntary group set up to bring a former slave hospital back into use, with an evening event to demonstrate the building’s potential to create a better future for all Bajans.
Mark was very pleased to help Grantley Adams Memorial School, and a voluntary group set up to bring …