The mining process starts after geological, mining and geotechnical studies have been completed

as well as the prospecting and sample testing to determine both the quality of the slate and the potential reserves of the deposit.

There are two mining systems: open-cast quarrying and underground mining.


Once the best
deposits have been selected in the quarry,

the rock is sawn into large blocks of slate
using wire sawing machines. These blocks are then divided into smaller pieces called "rachones", which are transported by heavy trucks to the processing plant.


These “rachones” are
then sawn into parallelepiped blocks

whose dimensions determine the size to be produced. The
resulting blocks are then distributed to the splitting areas.


This is the
manual operation

in which highly skilled workers using chisels and hammers
split each block into thin sheets following the exfoliation planes of the slate. Nowadays, laminating machines are also used to carry out this process.

Cutting and dressing

At this stage, the slate sheets are cut to the different commercial formats and sizes

by bevelling the edges of each piece to minimise the capillary effect and facilitate the sliding of the water once the slate has been laid on the roof.

Nowadays, most quarries have automated this process, using machines that cut and hole the slate.

Selection and packaging

Once it has been cut to size,

chamfered and holed, each slate undergoes a sorting process that determines its commercial classification, based on both technical and aesthetic criteria.

After their classification, the slates are packed on wooden pallets for storage and transport. Each pallet is marked with the corresponding classification and a label with technical information about the product is attached.


Slate Selection and
quarry grades

As mentioned above, at the end of the selection
process all quarries classify their production into different 'grades'.

As there is no any objective reference in this respect, there is little consistency in the market when it comes to defining the characteristics of a specific classification.

Our customers have greater transparency when selecting our products, as all the slates supplied by PMG are classified and packed separately on their corresponding pallets, which are duly labelled with the commercial classification of each product.

Our success is based on the quality and rigorous selection of our products, which are certified in the most demanding countries due to their proven features under all climatic conditions.