The vaults are built without any shuttering!

Firstly, flat bricks (24cm X 12 cm X 4 cm) bricks are made from good quality earth (for example, that traditionally used for building granaries). These are then used to build the vault, supported on the load-bearing walls.

The bricklayer, using a mortar made from the same earth, starts the vault by laying the first courses against one of the gable walls.

A cable made of 6 steel wires coiled together is stretched between the two gable walls, at the height of the base of the vault. This defines the central axis of the vault, and a cord fixed to a sliding ring on the cable acts as a guide to ensure that the bricklayer maintains a constant radius for the vault. Towards the top of the vault, the bricklayer adds a couple of fingers width to each joint to develop an ogival (catenary) shape.

The builder alternates work on the top of the vault, which requires some waiting time between each course for the mortar to dry, and the sides, which are easier to construct.

Buttresses are formed on the completed vaults by raising the side walls by 8 to 10 courses of large bricks, and by filling the gap so created with plain earth. The height of the buttresses depends on the client’s needs - many prefer to raise them high enough to make a flat roof terrace over the vault (and the flatter the roof, the more resistant it is to erosion during the rainy season).

Finally, the roof is water-proofed, using plastic sheeting (locally manufactured FasoPlast, costing around 400 CFA francs / square metre), over a smooth coat of mud mortar. The sheeting is then covered with a rendering of enriched mud mortar (using traditional adjuvants), which both protects the plastic from damage by the sun, and provides additional protection against heavy rains. It also acts as a warning signal to the proprietor - if the (black) plastic sheeting is revealed after heavy rains, then it’s time to repair the rendering!