The corner posts or end posts of stair rails are called newel posts. The posts serve as support for the entire rail system and must be securely attached to the floor. However, attaching a newel post to a concrete floor is difficult. Nonetheless, the do-it-yourselfer with little or no experience can attach a newel to a concrete floor in less than one hour.
Locate and mark the center mark for the newel post, and place a pencil mark on the concrete where the newel post will be set. Locate the center of the post base, as well, and mark it with a pencil.
Drill into the concrete with a hammer drill fitted with a 9/16-inch masonry bit. The bit must be at least 6 inches long, however. Begin drilling slowly into the concrete at the pencil mark that denoted the center of the post on the concrete. Press down on the drill slightly and allow the drill bit to do the work.
Hold the drill at a 90-degree angle to ensure that the concrete anchor is inserted straight. Place a framing square onto the concrete and at the back side of the drill to gauge its angle relative to the concrete angle.
Wash out the drilled hole with a hose or blow out the concrete powder with an air hose. Wear a dust mask and eye goggles, however, before proceeding.
Insert a threaded concrete anchor into the hole. This type of anchor is threaded on the outside and inside, and that allows the anchor to grab the concrete on the exterior while providing a threaded surface on the interior for a bolt. Tap the anchor into the hole with a hammer. The anchor is slightly flexible and will not fully expand until the bolt is inserted.
Insert the double threaded bolt into the anchor. This 9/16-inch bolt has two threaded ends. It is three inches to four inches long, with half being fine threads for the anchor and the other half being course threads for the wooden post. Tighten the bolt into the anchor by placing a 9/16-inch nut on the end and turning it with an adjustable wrench. Tightening the nut will also tighten the double bolt that rests in the anchor.
Remove the nut from the bolt and place the newel post onto the bolt, aligning the center mark on the bottom of the post with the anchor bolt. Thread the post onto the coarse threads of the anchor bolt. Tighten the posts onto the bolt and tight against the concrete floor.