Posted: 2017-12-07 17:26
Detail of End of Bed - Note Circular Grain Patterns from Burls Elevated Bed, Shelves and Desk
The main door into the building off the courtyard had an almost mediaeval feel to it. Decorated, but quite simple, defence was clearly a design consideration. Other similarly robust doors led to numerous corridors but it was not possible to see them much of the building is in too dangerous a condition. Apparently the kasbah corridors were labyrinthine and it was common to get completely lost. There were also massive dungeons which had many unfortunates incarcerated under the cruel reign of the Glaoui Clan. These have now been filled in to prevent the ground floor from collapsing.
The problem is that lime renders are stronger than earth renders. Whenever there is a build-up of materials in construction, the rule is that each subsequent layer should be weaker than the previous. Natural materials micro-move - they settle, they expand and contract, they can react to changes in their environment. This is one of their assets. However, the weaker the material, the more it will move. As Morison states, If the weaker plaster beneath a strong lime finish coat can move more than the finish coat, you will ultimately get delamination between the two coats which will lead to eventual plaster failure.
Stonemasons Seán, Brian and Séamus from Tir Conaill Conservation are very experienced, well used to working with lime. However, they had never worked with earth before. They took to it like ducks to water. Typically masons will mix earth mortars in a trough with spades. However, these guys found that the clay in the sub-soil was so strong and the tiny percentage of quicklime made the mix so stiff, that it was easier to mix by foot - literally dancing the mortar into existence. What a great way to build!
Initially the article deals with the incompatibility of earth and lime plasters used together. A common mistake that the author, Andrew Morison, comes across is people using an earth render for their base coat (scratch coat) and their straightening coat, and then using lime for the final coat because they perceive that it is more durable than earth. They think that this will provide increased protection for their building.