Lightweight render systems have grown in popularity in recent years due to increased awareness of the disadvantages of sand and cement render. Lightweight render systems are ideal for circumstances where the substrate requires either vapour permeability or flexibility; this is because these systems tend to contain lime, which offers both of these characteristics.
Lightweight render systems differ from sand and cement systems due to the fact that they typically consist of far more components and are much less likely to crack and wither away. Sand and cement renders are notoriously bulky, unforgiving and unbreathable. They tend to have a poor reputation for being unreliable and prone to cracking, so people turn to thin coat render systems and lightweight render systems for an ideal solution.
So what does a lightweight render system consist of? How do you install it and when would you install it? We’re going to be answering all of these questions in today’s blog post!
Components of a Lightweight Render System
In an EWI Pro lightweight render system, the components consist of an optional substrate primer; the Lightweight Basecoat; the Premium Basecoat; Fibreglass Mesh; a render primer and finally a through-coloured Silicone Render.
The key components that make this system ‘lightweight’ is the EWI-269 Lightweight Basecoat, which is a lime-based basecoat, with an air content of approximately 29% and a bulk density (once set) of approx 1.2 g/m3. The Lightweight Basecoat binds gently to substrates, offering a level of flexibility that ensures crack resistance. The great thing about this basecoat is that it is highly versatile; it’s suitable for a wide range of substrates and works especially well on high performance blockwork.
The second component that enables the system to be lightweight is the thin coat Silicone Render. This is applied on top of the Lightweight Basecoat (details below) and because it’s so thin (it’s applied only a couple of millimetres thick) it is easily flexible and therefore is able to work well in conjunction with the Lightweight Basecoat.
We always recommend using a vapour permeable render on top of the Lightweight Basecoat so as not to hinder its permeability; a Silicone Render is perfect for this because it is very breathable so moisture can easily escape through its structure.
How to Install a Lightweight Render System
The method used when installing a lightweight render system generally depends on the substrate. So we’re going to outline the two main ways of applying the system:
Applying the Lightweight Render System onto Ordinary Masonry
When applying a lightweight render system onto ordinary masonry, the substrate needs to be clean, dry and dust-free before any work is carried out. The substrate will also need priming with our Water Based Primer to reduce its absorptivity.
Once this has been carried out, the Lightweight Basecoat should be applied with either a trowel or a spray machine up to a thickness of 20mm. The Basecoat needs to be left to go off, before the Premium Basecoat is applied on top.
The reason we recommend applying an additional basecoat is because our Premium Basecoat is the strongest basecoat in our range; it’s vapour permeable and has strong adhesive capabilities. In the UK, the harsher weathers can have a damaging effect on softer materials, hence the repeated use of sand and cement render.
We suggest using the Premium Basecoat on top of the Lightweight Basecoat as a way of strengthening the system against the more challenging climate and to ensure an extra level of crack resistance. Fibreglass Mesh should also be embedded within the Premium Basecoat to enhance the tensile strength of the system; it’s all about building up compatible layers to achieve a sturdy finish.
The Premium Basecoat should be left to set entirely, and then the SiSi render primer should be painted on top and left to dry. All of the aforementioned layers are applied with the intention of levelling and strengthening the substrate; the final layer of the lightweight render system consists of the Silicone Render which is both decorative and functional.
The Silicone Render works well with both materials, allowing for movements within the building structure without cracking, while also enabling the system to breathe. The render is applied at a thickness that corresponds with the chosen grain size; if it’s a 1.5mm grain size then the render is applied at 1.5mm. It can be tinted to create any colour and contributes towards a long-lasting and incredibly durable render system.
Applying Lightweight Render Systems to High Performance Blockwork
Applying this system to high performance blockwork is a little different because these types of blocks tend to be really absorptive and so the correct method of application is very necessary to ensure no cracks.
With a high performance substrate, you would forgo the priming stage and skip straight to applying the Lightweight Basecoat. The key difference, however, is in your method of application of the basecoat. It needs to be applied in two passes; the first pass should be applied at approximately two thirds of the total thickness – so around 12mm. Leave it to pull back slightly and then apply the final third.
Once both passes of the Lightweight Basecoat have set completely, you would apply the Premium Basecoat and follow the same process as outlined above.