Clean the damaged surface of the existing concrete pad with a pressure washer. Rub over tough stains and concentrated debris with a stiff-bristled broom. Cover the wet concrete with plastic sheeting, and let the slab set for at least 12 hours.
Cut 1-by 4-inch boards to length with a table or circular saw.
Remove the plastic sheeting from the surface of the concrete slab. Install a 2-inch-square forming stake tight to each corner of the concrete slab with a 2-lb. sledgehammer. Place one stake every 4 feet in between the installed corner stakes.
Set the 4-inch-square piece of wood (gauge block) onto the surface of the concrete slab, near a corner. Place and cut a 1-by-4-inch board between the forming stakes and the concrete slab. Align the top of the 1-by 4-inch board with the top of the gauge block. Drive a forming nail through the forming stake and board to hold the board at the right height. Repeat the procedure at each forming stake to form the edges of the concrete top coat.
Mix one-part Portland cement, one-part coarse sand and two-parts pea gravel for top coats thicker than 1/4 inch, or mix three-parts coarse sand to one-part Portland cement for top coats 1/4-inch thick or thinner in a wheelbarrow. Add water to the mixture until you achieve the consistency of thick oatmeal.
Mix one-part fine sand to one-part Portland cement in a plastic 5-gallon bucket. Add water to the mixture until it has the consistency of thick paint.
Pour the mixture from the plastic 5-gallon bucket onto the surface of the concrete. Spread the mixture across the slab with a paint roller attached to an extension pole.
Pour the top coat mixture from the wheelbarrow into the forms. Spread the top coat around the slab with a concrete float.
Level the top coat by placing the long 2-by-4-inch board across the top of the form boards. Move the board in a sawing motion as you slide the board along the concrete slab.
Remove the forming stakes and forming boards from the concrete slab after the concrete top coat as cured for four to five days.