The gravel in the honeycombs forms a rough surface onto which the loose gravel grabs hold. Because of this, the top layer will only shift minimally. Covering the honeycombs with a layer of gravel not only creates the most aesthetically pleasing effect, but also maximises the protection of the honeycombs. However, this top layer cannot be too thick, or the effect of gravel stabilisation is lost. Ideally, the top layer should be 1-2 cm.