14 RCI 0714

RCI JULY 2014

ISSUES & SOLUTIONS Achieving lasting results with monolithic render finishes 014 JULY 2014 RCIMAG.COM Agree? Disagree? Are there any issues on any aspect of the roofing, cladding or insulation sectors you would like to see discussed in future Issues & Solutions columns? If so, email the editor: mdowns@unity-media.com The Issue At last, an air of confidence seems to be returning to the construction market. There is a tangible upward curve in both new housing development and commercial building that has seen growth in the sector return to 2007 levels. While this is good news, optimism is tempered by the recognition that margins remain tight and project timescales short. As a result of these pressures, the upgrading of a building façade for a – relatively – quick makeover is becoming common, while rainscreen cladding continues to remain the façade covering of choice for the new-build commercial sector. It is well recognised that a new façade, whether on a new building or old, delivers aesthetic benefits. Creativity is an architect’s stock in trade and a new façade is an opportunity for self-expression which has seen an extraordinary burst of creativity in architectural design with much imaginative use of large format claddings. This revitalisation has led to many eye-catching overcladding projects of new and existing buildings as well. Another equally popular choice is a render topcoat to create a monolithic finish. However it can be hard to achieve lasting results that don’t suffer from cracking and other age-related problems. The Solution Externally clad walls which incorporate insulation are normally constructed as a double skin. The insulation shields the internal layer and an air gap, with a decorative outer skin providing the weather protection and aesthetic effect. Taste dictates that not everyone desires the same finish and there is a multitude of suitable materials, colours and textures available. Although a rendered finish is usually associated with block or masonry, the use of a good render backer gives additional scope for a coarse, textured or smooth finish that can be either painted, pigmented or left natural. The monolithic finish will of course eliminate joint shadowing, which can be an issue to some. Achieving a desirable monolithic finish that will satisfy the design brief and perform well in the long run requires the use of a good substrate. A stable render backer board helps achieve a better uniform exterior finish. Furthermore, to avoid cracking, it is important that all fixings are secure Monolithic render finishes continue to be popular. Ged Ferris, marketing manager at Cembrit highlights some common issues while offering a straight-forward solution and seamless joints are made between boards. It is a simple process to install a render backer board but there are several things to bear in mind when carrying out an installation – all will contribute to the success of the process. When selecting a board, it is an advantage if the board is lightweight. This helps with manoeuvrability onsite as well as during the actual fixing process. Cembrit PB board, which incorporates polystyrene beads in its construction, offers reduced weight over comparative boards. The make-up of the board also makes cutting easier: there is no requirement for mechanical cutting equipment as all cutting can be done with conventional hand tools. This also helps with safety eliminating the risk of nuisance dust created by cutting with mechanical equipment. The installer will also need to be aware that fixing too close to corners or edges can damage the boards, making the achievement of a lasting monolithic finish more difficult. The PB board has reinforced edges to solve this problem. To ensure that the fixings can be completely covered with render, the edges are chamfered so that the fixing head is below the surface of the façade. As Cembrit PB boards are designed to fit neatly together, stability at the butt joints is maximised, which further reduces the risk of the render cracking along the joints. Each of these characteristics contribute to making Cembrit PB a stable base reducing the risk of the render cracking along the joints and eliminating spalling above the fixing, which also looks unsightly on the finish. With the increase in demand for lightweight external cladding systems, it is important that installers are up to date on the installation of render-backer boards in rainscreen cladding applications. Traditionally, many have associated a rendered finish with block work or masonry and although this association is correct, the use of a good render backer offers an alternative, less expensive approach to monolithic finishes. The design benefit of this is that a monolithic appearance can be achieved with the advantages of lightweight construction. In short, a quality render backer helps achieve an excellent uniform exterior finish with secure fixing and seamless joints. Furthermore the façade can incorporate thermal efficiency and be pleasing to the eye for many years to come. www.cembrit.co.uk “In short, a quality render backer helps achieve an excellent uniform exterior finish with secure fixing and seamless joints”


RCI JULY 2014
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