Round and Round She Goes
A project profile on a radius staircase
by Bart Sacco

The photos seen here illustrate a job I did a couple of years back involving a massive radius staircase connected to a 3,000-square-foot veranda which sprawled from a 21,000-square-foot home in northeastern Pennsylvania (see photo 1).

The bluestone-ashlar veranda (see photo 2) features stamped concrete using Brickform TM-100 texture mats from Rafco Products’ Creative Images line. The job also included using SS-100 Sierra Seamless texture skins — which allow texture to be imprinted over large areas without bond lines — for the borders and integrating them to wrap in with the steps. The color hardener is CH-825 Slate Green and the release agent is RA-600 Light Gray, both from Rafco Products. The sealer used on this job is Glaze ’N Seals’ “Wet Look” lacquer, a crystal-clear, high-solids acrylic coating designed to protect concrete surfaces.

As for the massive stairs, the tread is 18-inches deep and the rise is 4-inches high. The top step is 53 feet in radius and the bottom step is 76 feet in radius. Each individual tread was produced from a continuous pour.

The general contractor had already provided the below grade work and the associated block work (see photo 3) to ensure there would be no movement with the freeze-thaw weather conditions in the region. The staircase started out well below the frost line with solid footings and piers.

A block sub-frame of the steps (see photo 4) was built to a smaller dimension of the shape of the final staircase to allow enough room for an adequate amount of concrete on top and in front of the block work. Then the blocks were filled solid with concrete. This gave us a solid surface to which we could mount our concrete formwork and enabled us to hit our desired grade with accuracy and keep the perfect radius. This method also allowed us to build the final product from the top step down, instead of from the bottom step up. Building from the top down permitted us to produce a very clean-looking vertical riser with a perfect 90-degree angle at the rear of the tread and the bottom of the riser.

The formwork was custom made to suit the job (see photo 4). We used 3⁄8-inch flat stock cut into 21⁄2- by 18-inch strips for the brackets. The metal was bent on a metal break to leave a 10-inch flange for the bottom and an 8-inch flange for the upright. We offset a #3 rebar and welded it to one side of the bracket for support. (I think the flat stock alone would have been strong enough, but I wanted to make sure there was no deflection once the concrete was placed.)

The rebar was offset on the brackets to allow enough room for our drills to get in, drill the pilot holes and set the masonry fasteners. The face of the formwork was standard grade 1⁄8-inch flat stock metal, cut 8-inches wide and 20 feet long for the faceplate or the bulkheads. We would have used longer lengths if we could have to minimize our splices, but 20 feet was the longest available.