Applying Coloured Render to Thermalite Blocks

Coloured render is a popular choice for many homeowners, but on a Thermalite substrate finding the ideal materials to create the coloured render effect can be tricky. Renowned for being one of the most popular high performance building blocks, Thermalite offer excellent thermal performance, breathability and moisture resistance. The only thing about Thermalite blocks is that they create an extremely soft substrate and therefore can be tricky to render. Ideally, Thermalite blocks need finishing with a material that matches them in softness and flexibility in order to prevent cracking.

We have seen so many cases where an inappropriate render has been applied to a high performance block substrate, and we know that many builders experience problems when faced with high performance blockwork, as knowing the right quantities of materials can be extremely tricky and a bit of a balancing act. Luckily, here at EWI Store we have come up with the perfect solution for how to apply coloured render onto Thermalite blocks.

The Perfect Basecoat for Coloured Render on Thermalite Blocks?

Our Lightweight Basecoat is ideal for use with Thermalite blocks because (as the name suggests) it’s incredibly lightweight and therefore works well in conjunction with the Thermalite, providing a stable base for the coloured render. Because the Lightweight Basecoat contains lime and perlite, it has the breathability and flexibility of the lime while also maintaining the strength of the perlite; it’s therefore ideal for a soft and lightweight substrate such as Thermalite, because the Lightweight Basecoat will resist the common issue of cracking and render failure.

When using the Lightweight Basecoat with Thermalite blocks, you can use fibreglass mesh to give the system extra strength and crack resistance. An alternative is applying the Lightweight Basecoat with no mesh, then leaving it to set, and then applying a layer of the Premium Adhesive with mesh before the coloured render.

Most recommended, however, is using the Lightweight Basecoat and then applying a ‘tight coat’ on top. This is where you apply a second coat of the basecoat in a thin layer, which is then rubbed up or sponged before coloured render is applied.

Applying the Coloured Render to Thermalite Blocks

When choosing a coloured render, there is a vast array of different brands and different renders that all offer a variety of benefits. Silicone Render is a well known coloured render, offering breathability and vapour permeability. Silicone Render is a thin coat coloured render and, as the name suggests, is applied in an extremely thin layer which means it is highly flexible (see below for a video demonstrating just how flexible it really is!).

Flexibility is an important quality to look for when choosing a render for Thermalite blocks, as the blocks are so soft that they very easily expand and contract during heating and cooling. A hard and unforgiving render such as sand and cement would only crack with the movements of the blocks. Check out our blog post ‘Sand and Cement Render on High Performance Blocks’ for more information!

We recommend using Silicone for rendering Thermalite blocks, as it will compliment the substrate with its vapour permeability and will also prevent water from getting behind the system and into the blockwork. It’s important for Thermalite blocks not to get wet, because during the process of drying they can very easily crack due to their softness; Silicone Render creates an impregnable shield against water ingress.

And there you have it – how to apply coloured render to Thermalite blocks. The process is very simple and the materials really save going through the experience of a failed render. For any further questions about using coloured render on Thermalite blocks, call up our technical team or leave a comment below! We’re always happy to give our free expert advice.

Applying render to a range of substrates…

Recap of Materials for Applying Coloured Render to Thermalite

 

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