The term sandstock brick gets misused a lot and these days, in particular it often gets applied to many mass produced bricks that have a textured surface, but these are sandstocks in name only, they are not true sandstocks. Sandstocks are often referred to as convict bricks, this is partly true, many convict bricks are indeed sandstocks, but not all sandstocks are convict bricks, as sandstocks have a rich history in both Europe and North America.
Most simply a sandstock brick is a handmade brick made by pressing clay into a brick mould dusted with fine sand. This process results in compression marks or an elephant skin texture to develop on the face of the bricks. These compression marks are further developed during air drying before they are fired in the kiln. As you can see by the picture below, the true characteristic texture of a genuine sandstock brick is unmistakable.
Above: Our Heritage Soft Red sandstock brick.