Learning about vaults on the fourth week
The last week of the course has arrived. With it comes a central part of the learning process, learning the secrets behind building a vault. To help us sharing this knowledge we received the architect Miguel Rocha from CEDAC Terra that counts with numerous experiences with arches and vaults in Portugal and Spain. His lesson after the completion of the first two arches made clear several aspects that only after practice can be fully comprehended.The third and fourth arch were made with full attention to the details and the result can be seen. The practice makes the master!
Before starting the vaults we did tests for the mortar. The vaults mortar has to be liquid to viscose and with particles under 1mm. We tested several compositions between fine sand, sieved earth, lime and cement. The bricks were glued to each other and to the wall. At the end the chosen mix was 4 of fine sand, 2 of sieved earth and 1 of NHL3,5 lime. This didn’t crack during the tests, had a good adherence to the wall, was the most breathable due to the lime and had the biggest content of earth, adding the properties of clay to the mix.
The bricks are smaller then the wall bricks, to help contradict gravity and make them stay glued. The vault technique used doesn’t have the support of a centering, making it so important the way mortar glues to avoid unpleasant surprises. The bricks weight is around 2,5kg and the dimension is 21x10x6,5cm. So different from the weight and dimension of the wall bricks: 6,5kg and 29x14x8,5cm. Another difference between the bricks, is the pattern in bas-relief done to allow the mortar to fill the gaps and create a suction phenomenon, allowing the brick to stay glued while the mortar doesn’t cure. This effect is created due to the capillarity bridges formed between the elements of the mortar and the brick. To know more about this phenomenon go to this video.
We had several days with temperatures above 30ºC which makes it difficult to work with the lime mortars. Shadowing and watering were very important to make it work properly.
The bricks are placed first horizontally, at the point that the curve and weight challenges gravity to much, vertical bricks are placed towards the wall forming arches. It is important that arches are formed in every direction, in the horizontal and vertical sections to conduct the load towards the walls and avoid the collapse of the vault before closing. To assure this, guidelines are placed between the intrados of the two first vault arches. Brick by brick arches and lines are closed and the vault gains shape.
The course finished before the first vault was closed, but the techniques was passed and a couple of volunteers stays to help finishing and learn more.
We would like to thank to all participants of this first learnBION course, it was a great team! A family we must say!
