The production of slate

Extraction of the rough blocks at the quarry

The rough blocks of slate are extracted from the quarry tanks to powerful explosives and more recently thanks to diamond strings.

Then the blocks of slate are transported by lorry to the manufacture to be transformed.

Primary exfoliation

This operation consists in dividing the uncut blocks following the fissility plan of the shale. The suitable thickness will depend on the saw used and it must not be, in any case, superior to a third of a diameter of the disc. A flat-ended pneumatic hammer will be used for this operation. Once the blocks are separated, a crane will transport them to the cutter’s table.

Sawing

Once the block is placed on the sawn table, it will be cut in parallelepiped cubes of different dimensions (or strips) depending on the format of the slate we want to obtain further.

These strips will be stored in containers full of water until the next production phase.

Splitting

This operation of manual cutting consists in splitting thin sheets from the slate strips which thickness must be determined by the figurer. This phase of production requires great ability of the person who carries it out.

Once more, the fissility plan must be entirely respected in order to optimise the technical and mechanical qualities of the product once placed on the roof ; this way, running of the water on the roof will be better.

Sizing

This phase allows giving the definite dimension to the slate.

Formatting is carried out either in individual machines where the sheet is sheared between a fixed horizontal blade and a contra-rotating blade, or in automatic machines.

Selection

Selection consists in grouping the slate pieces following some parameters previously established. We will obtain four different selective parameters of the finished product as follows :

• Optima,
• Superior,
• Naturelle or Rustica.