The effect of a thin weak layer covering a basalt block on the impact cratering process

► Impact cratering experiments on a basalt block covered with a mortar layer were conducted at the velocity of 2 and 4 km s−1. ► The mortar layer thicker than a 1.5 projectile length can protect the basalt from the cratering completely. ► The crater scaling law in the strength regime was improved for bedrock covered with a weak layer. ► The effect of the weak layer was expressed by the exponential equation of the thickness normalized by the projectile length.