Cut out and replace any pieces of wood on the posts that may be rotted. Fashion and place temporary support for the load on the porch post while the old portion is being cut out and replaced. Each post should be secure before covering it.
Measure the exact length of each post to be covered. Mark the adjustable aluminum post wrap pieces to the exact lengths subtracting 1/8-inch for expansion. Four pieces will be required for each post.
Cut the pieces to length with a saw appropriate for cutting aluminum.
Set two pieces of the aluminum post wrap around half of the post and fit the tongue of one piece into the channel of the adjacent piece. The joint that is being created will run vertically in the middle of one side of the post. A helper standing on a stepladder may be very helpful in managing this job on taller porches.
Squeeze the two pieces together at the top, bottom and middle until a firm, snug fit has been achieved on two sides of the post with these two pieces. Set this compressed section aside temporarily.
Set the remaining two pieces of post wrap around the other half of the post and fit the tongue of one into the channel of the adjacent piece. Again a helper standing on a stepladder may be very helpful.
Compress these pieces until about ¼-inch remains that will need to be compressed at the joint. Leave this section in place around the post.
Set the first section back in place around the post and use clamps to hold it in place.
Fit the tongues and grooves of both sections together. Clamps may be required on both sections. Gradually work to squeeze the two sections together in the remaining two joints. The channels and grooves need to align and be even on all four pieces.
Add an appropriate post cap to the top of the post in situations where the post does not support part of the structure.