Here is a step by step description, and if you scroll to the bottom there is a video about dry stone walling from Minera School of Slate.
The number of slate bricks you will need will depend on the type of wall and whether it’s for a fireplace with a lot of corners, or a long wall. Order a few more bricks so you have a little more to choose from, and as a minimum 10 per cent more than the size of the finished wall.
For use where there is limited space and low weight is important. Due to the bricks’ narrow depth, the variation in both length and height will be more limited. You will always need to use cement on the backside in this example.
A very useful size that looks great aesthetically and is very stable. Beautiful for decoration both indoors and outdoors, for façades, fireplaces, walls and other brickwork. These are usually cemented on the backside.
A sturdy slate brick to be used where there are no limitations in terms of space or weight. Used for decorative masonry and outdoor retaining walls. With a greater depth, the length and height will be more varied and will have a more solid and rough appearance. This size can also be used for smaller retaining walls and backfilled with loose, drainable material.
It is important to put coping stones on the top of the wall to prevent water penetrating, which can also lead to salt and limescale build-up, as well as frost damage.