What are the Advantages of Steel Frame Buildings?
Steel frame buildings are, as the name suggests, constructed of heavy-weight steel beams that are used to form the building shape and are then fitted together to create joints. A real benefit of this type of building is that it is extremely strong, durable and easy to assemble. The steel is made-to-measure, prepared off-site and then transported in parts.
There are many materials that can be used to form the exterior surface of the steel frame, but typically a sheathing board is secured to the frame before a cladding or render is installed on top. For non-residential buildings, Mineral Wool insulation is typically fixed to the sheathing board (with adhesive and fixings) and the thin coat render system is applied on top. For residential projects, Mineral Wool insulation is installed within a cavity, before a render carrier board is secured to the steel frame on the outside. Quite often you can find steel frame buildings with a brick cladding forming the exterior surface as well.
Steel frame properties offer the added value of fire resistance, as steel is non-combustible and will not bend or warp. Combine this with our Mineral Wool external wall insulation system, and you’ve got yourself a building with excellent fire performance. Further to this, unlike timber frame buildings there’s absolutely no risk of rot and termites with a steel-frame – so you’re guaranteed structural integrity throughout its lifespan.
Installing Render Carrier Board onto Steel Frames
Usually, a render carrier board (RCB) will be installed into the steel battens to provide a surface that is ready for rendering. Depending upon the manufacturer’s instructions, a 3-5mm gap should be left between the render carrier board joints. A breathable joint tape should then be applied across each joint to prevent a build-up of condensation in these gaps.
The render carrier board shouldn’t need priming prior to being rendered, as its surface is intended for render anyway.
Applying the Basecoat Layer to the Render Board
We recommend that you use the EWI-225 Premium Basecoat when rendering a steel frame building. This is because it is breathable, high strength, water-resistant and has high elasticity. To prepare the basecoat, simply mix each 25kg bag with 6.5 litres of clean, potable water using an electric paddle mix. Once fully combined, leave the mixture for 5 minutes and the re-mix again before it is ready for use.
The Premium Basecoat should be applied to the substrate using a notched trowel at a maximum thickness of 6mm. Beading should be embedded into the basecoat layer, as well as Fibreglass Mesh strips. Each strip of mesh should overlap its neighbouring strip by 10cm. It’s essential that the mesh is embedded into the middle of the basecoat so that there is no contact with the render carrier board underneath.
Priming the Basecoat
Before applying any render, the basecoat needs to be primed. This is to ensure strong adhesion and create a consistency of colour across the facade (our render primers are tinted to match the render). We recommend the use of EWI-333 which is the ideal topcoat primer for our silicone-based renders. Simply paint the primer onto the substrate using a brush or roller, and then leave for 12 hours to dry.
Applying the Render Topcoat
Technology has greatly improved the breathability of renders; we know that coloured renders are extremely popular these days, but breathability is a really useful characteristic of our thin coat renders, so we recommend the use of EWI-075 Silicone Render for steel frame buildings and render carrier board. The other added benefit is that this type of render can be tinted to create almost any shade, so if you’re really keen on a particular colour we can match it up for you.
The render should be trowelled onto the substrate at a thickness that matches the chosen grain size, so if you’ve chosen a 1.5mm grain it should go on at 1.5mm thick.
The trick with our thin coat renders is to rub them up with a plastic render float. Simply use circular movements to bring out the texture of the grain and get a nice even finish across the facade.
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