New Ziegel Block Building, New Coloured Render

When thinking about applying a decorative finish to Ziegel blockwork, it’s important that the materials you are using compliment the substrate (we’ve written previously about failed renders caused by this). Ziegel blocks are known for fire safety, thermal performance and excellent indoor air quality. With that said, the right materials are required in order to compliment the functionality of the substrate and subsequently reduce cracking.

At EWI Store, we have a range of solutions for applying coloured render to high performance blockwork successfully, so let’s take a look at the process and the materials required to ensure crack resistance and a lasting finish.

Why Build with Ziegel Blockwork?

In order to understand the kind of render that would be best suited for Ziegel, we need to take a look at what exactly Ziegel blocks are and what properties they have. Ziegel blocks are renowned for being high performance because they have excellent insulating capabilities.

Their high thermal performance is due to the air channels that run vertically through each block creating a honeycomb effect, while the clay itself has more air pockets made by sawdust that is burned off in the kiln during the firing process. Ziegel blocks are also a breathable building material as they can maintain the equilibrium of humidity by storing and releasing heat and moisture, helping to maintain room comfort and healthy indoor air quality all year round.

Ziegel are also a highly dense material, creating a uniform substrate that offers reduced thermal bridging with a quick and easy construction process. Although Ziegel is a high performance block, it does need finishing with a protective layer to prevent weathering. This is where coloured render systems are ideal, because the technology of the system means that the substrates functionality is in no way hindered by the coloured render, instead the materials that go into the render system compliment the substrate.

Applying the Basecoat to Ziegel Block

Ziegel block creates a uniform, continuous substrate which is incredibly easy to render in terms of creating a smooth surface; the only area that requires close attention is using the right materials and the right method of application. You can decide based on the climate and weather conditions whether or not you need to apply a two-coat system or a three-coat render system for this kind of blockwork. The default for the UK tends to be the three-coat system because the Lightweight Basecoat and render on its own will not withstand the weather conditions.

Two-coat system:

The two-coat system consists of the application of the Lightweight Basecoat, then a tightcoat and then a render.

In a typical render system on an ordinary substrate, a substrate primer would be necessary to limit the absorptive capacity of the substrate. However, when rendering a Ziegel substrate, to limit the absorptive capacity of the substrate you do not need to prime. Instead, you spray apply a first pass of the Lightweight basecoat at approximately two thirds of the thickness it should be applied at – around 12mm. You leave this to ‘pull back’ and dry slightly before appyling the final one third to take the basecoat up to its total thickness.

The Lightweight Basecoat needs to be left for a period 0f 24-48 hours to dry, then the tightcoat is applied. This consists of another thin layer of the Lightweight Basecoat; it is applied to the dried basecoat and is sponged or rubbed up to achieve the required texture. Once the tightcoat has been applied, it can be primed and painted or primed and rendered using a ready-mix render (e.g. Silicone or Silicone Silicate). You can also use Mineral Render (and then paint with Silicone Paint) or you can use Monocouche render. The main thing here is that the tightcoat must be primed if you are using a ready-mix render such as Silicone or Silicone Silicate, because otherwise blooming may occur across the lime basecoat.

Three-coat system:

A three-coat system is the standard system that is recommended for use in the UK. The three coat system involves applying the Lightweight Basecoat in two passes, as outlined above. Once the Lightweight Basecoat has cured (after 24-48 hours), a layer of the Premium Adhesive with Fibreglass Mesh embedded is then applied on top. The Premium Adhesive is then primed using a render primer, before the render of your choice is applied; whether it’s Silicone, Silicone Silicate, Mineral or Monocouche.

The reason that the Premium Adhesive is applied as an extra layer is because it is far stronger than the Lightweight Basecoat, and when applied with a Fibreglass Mesh embedded within the adhesive it provides the required tensile strength to be able to withstand harsh weather conditions without cracking.

Applying Silicone Coloured Render to Ziegel Block

When applying coloured render to a Ziegel substrate, we really recommend the use of Silicone Render as it’s incredibly flexible, breathable and hydrophobic. It will therefore resist any cracking, prevent water ingress and allow water vapour to escape from the building fabric. It’s currently our most high performance coloured render and is an extremely versatile and popular solution for a wide range of substrates.

Silicone Render can also be tinted to create any shade of colour (hence the name coloured render). If coloured render is of interest to you, you can view our full shade range using our render colour chart, or you can purchase a coloured render sample pot.

For any further questions about applying render to Ziegel block, contact our technical team or leave a comment down below – we are always happy to help!

We upload a new blog post every Tuesday and Thursday, so stay tuned for more content!

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