small pattern Ground protection mats 2×4 for apron small pattern ground protection boards 2×4 for Lawns protection 2 in. x 4 in. x 16 ft. Must use Ground ntact pressure treated lumber where lumber is at risk for poor air circulation, less than six inches from the ground, or has poor or no water drainage below the structure. #1 grade lumber has few defects, knots will be small and well-spaced.