He started by using our power plainer to even it out as best he could, and to remove the roughness the mill saw left behind. When that was complete he took the belt-sander to it and smoothed out any final imperfections. The next step was cutting the backside off to be able to mount it flush to the wall which required our chalk line and circular saw. With the back side now straight we could then square up and cut them to length. Once that was done he began the sanding it some more with the Random Orbital Sander starting with 100 grit paper moving to 150 grit, then 220 grit before finishing it by hand with 320 grit. He wet the wood with a damp cloth between each sand and allowed it to dry. This process raises the grain making it easier to smooth out the wood this is called "whiskering". Now that the wood was smooth he brought it inside to coat with a satin varathane 3 coats on each side.
To mount it he purchased some 1/2" black pipe nipples, 90 degree angles, and floor flanges and used Tapcons to attach them into the concrete wall.
They still have enough for a bench and other shelf but that's a project for warmer time.