2021-7-31 · Lay down your base of 20mm crushed rock at a minimum depth of 50mm. Spread and level the 20mm crushed rock using the back of a rake or straight length of timber. It is not advised to use a rake with the prongs down, as they tend to pull the larger rocks out leaving patches of stony material. Water the crushed rock LIGHTLY with a hose. Do not soak.