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Article Date: 10th March 2017

Catnic - Don't Skim the Details

Building Envelope - Catnic Beads - Plastering Beads - Building Components

Catnic - Richard Price

Buildings across the Gulf region share a distinctive style that often relies on the smooth, pristine effect of a high quality plaster finish blended with other modern materials such as metal and glass. It is therefore plaster, in part, which helps to bestow the area with its distinctive architectural aesthetic. Here, Richard Price, Technical Director at Catnic - the British manufacturer of steel building components - examines not only the role of plaster as a building finish, but also the best methods to achieve optimal results.

The exterior finish of any building performs two functions. Firstly it protects the surface of the building envelope, thereby avoiding damage caused by wind, rainwater, heat from the sun or sand ingress, for example. Secondly it provides a decorative finish that enhances the appearance of the building and reinforces its place within a cityscape.

When it is applied professionally a good plaster, or skimmed finish will protect the structure of the building from exposure to climatic changes, acting as a waterproofing sealant and a sanitary coating for the building to prevent the ingress of vermin and insects. It works too as a levelling coat, making both external walls and internal walls and ceilings smooth for their own aesthetic appeal, or as a base for the application of paint or other decorative treatments. In addition it provides a preliminary defence against fire and so also plays a role in helping to fireproof a building.

Despite correct maintenance, all too often a plaster or rendered finish can fail long before the lifetime of the building due to errors in the specification of important details. For example, plasterers’ beads may be considered commodity products, necessary to ‘get the job done’ and therefore left to sub-contractor discretion. This creates the risk of cost-cutting and potential quality compromise, yet they are a reliable method of achieving the high standard, sustainable finish that clients expect.

The right bead helps to achieve a neat, crisp and professional finish while also avoiding cracking and splitting, which can cause issues with the paintwork or wall coverings at a later date. Therefore the accurate specification of these components is integral to the long term performance of the building envelope.

We are witnessing the specification of Catnic beads and plastering profiles by name with more and more frequency, instead of the ‘equal or equivalent to’ approach of the past. It means there is no room for interpretation or misjudgement when it comes to ensuring on the highest quality beads are used to achieve the best possible plaster finishes.

By specifying by name, right down to the type of plasterers’ beads to be used in the internal and external finishes of a building, the specifier is safeguarding their own design intent.

Products from a reputable manufacturer with the right technical expertise will ensure the highest quality is achieved. A good bead is one manufactured from a thicker gauge of steel, providing rigidity and strength, helping to ensure a straight edge and slick precision finish. These properties will also ease site logistics because a strong, straight bead is faster and easier to install, helping to reduce time onsite, limiting snagging and improving labour costs too. Catnic’s galvanised beads are manufactured to a gauge 11% above the requirements of both British and European standards, while its stainless steel beads exceed these requirements by 25%.

In specifying such a product by name, architects can ensure that beads with adequate protection are installed. In doing so the overall finish of a rendered façade is secured for the long term. A well-made bead provides the right depth, helping to ensure the correct level of plaster is applied and therefore stopping the bead from showing through the finish. Punching and forming also needs to be of a consistently high standard and should comply with BS EN 13658-1:2005 and BS EN 14353:2007 as a mark of quality. It is also worthwhile selecting products in line with BS EN 13914 Parts 1 & 2: 2005, which provide guidance on the design, preparation and application of external rendering and internal plastering.

It is often the unique environmental factors of cities in the Gulf region that provides a challenge when achieving a sustainable, long term finish. High temperatures, combined with humidity, sand and airborne salinity all conspire to create a harsh environment for buildings and their materials. Here the advice of a manufacturer experienced in the specification of metal building products can prove invaluable. Galvanised steel beads should be used internally and stainless steel or PVCu should be installed externally. For areas of high moisture or in very damp conditions, stainless steel or PVCu are equally suitable.

In particular, PVCu beads should be selected for projects situated in the most aggressive climatic conditions. These can be specified for situations where galvanised beads are not recommended and internally in areas where high moisture or damp exists, in both cases providing an economical alternative to stainless steel.

Stainless steel products should be used where a cement-based render is to be applied. To ensure the longevity of the bead, the use of sand or water contaminated with soluble salts or chlorides in plastering mixes should be avoided. These are likely to increase the risk of metal corrosion. The presence of sea salts in sand used in plasterwork over galvanised beads will often cause rust staining and should also be avoided.

With new structures appearing almost daily out of the ground, the reputation of architects and owners hangs on their design and delivery. By ensuring even the small details are not overlooked, architects can have confidence in the resulting finishes.

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