Cantilevered concrete stairs forms the focal point of penthouse apartment

A feature concrete stairs forms the focal point of this penthouse apartment in the Liberties area of Dublin city.

This cantilever stairs is striking in its design and execution with 14 individually hand-crafted black concrete steps forming a strong contrast with the light grey concrete stairs wall and the glass panels to the open side of the stairs.

The 4.5m high concrete wall forms both an architectural feature and a structural element and was cast using a self-compacting concrete (SCC). The slenderness of the wall together with heavy reinforcement congestion and a lack of space resulted in an SCC mix being the preferred concrete type for this stairs wall. An SCC mix, with the cement type comprised of 50% GGBS, was used to produce a light grey concrete colour in contrast to the black concrete steps. Careful consideration was given to the placement of the SCC with a particular emphasis on form type, release agent and application, placement methodology and the rate of placement. This resulted in a finished wall with high levels of consistency of colour with few blemishes. When the formwork was removed the wall was polished to 100 grit to produce a buff finish.

The concrete mix for the stairs was designed through close collaboration between Brian Formwork and the Roadstone technical department with both an emphasis on the finished aesthetics of the mix and meeting the limiting values of composition as required by European standards.

Each of the 14 individual steps were hand crafted onsite site due to the small volume of concrete required using Roadstone sand and 10mm limestone aggregate as well as cement, admixtures and a black pigment. Once cast and with the required strength achieved, each step was polished to 1,500 grit to a matt finish to expose the coarse aggregate and, additionally to provide slip resistance.

The use of quality constituent materials including modern admixtures were seen as essential in producing the concrete for both the stairs wall and the individually hand-crafted steps.