Existing pole barns that have dirt floors can have concrete floors installed with little or no difficulty, providing that certain conditions are met beforehand. Concrete floors will spruce up your pole barn and allow you to use it for more than one use. The best news is that the average do-it-yourselfer can install his or her own concrete floors in one to two days, depending on the size and scope of the project.
Place concrete forms around the exterior of the pole barn poles with 2-by-4 lumber. Because pole barns are supported by poles, you can use the poles as support for the concrete forms. Find the highest corner of the pole barn and attach the first form board to the outside of that corner post, using 3-inch screws. Level the form with a 4-foot level and attach wooden stakes every 4 feet to level the lumber.
Stretch a nylon string across the first run of forms--from one post corner to the opposite--to make sure that the forms are straight. With one end of the string attached to the first corner and the other end attached to the opposite corner, adjust the centre of the forms so that it lines up with the straight nylon string.
Repeat the form process on the remaining sides of the pole barn, levelling and straightening the form boards as you proceed. Fill in spaces under the form boards if they are raised off of the ground for levelling; as you level the form boards, they may need to be raised off of the ground, leaving a space beneath the board, which must be filled with wood. Use 3-inch wood screws and scrap 2-by-4s to fill in spaces.
Coat the bottom of the poles on your pole barn with tar to prevent the corrosive effects of the concrete from damaging the poles. Use a brush to apply the tar up as high as the concrete will be poured.
Pour concrete into the wood forms and finish the concrete with concrete finishing tools. Use a concrete hand trowel and bull float to smooth the concrete, an edger to round the corners, and a control joint tool for placing control joints at 4-foot intervals in the concrete. Place a broom finish on the concrete, using a push broom, and apply concrete sealer with a pump-up sprayer after the concrete has set for 72 hours. Remove the forms after 48 hours, but don't use the concrete for one week to allow the slab to harden correctly.