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Top Tips for Preventing Cracked Render

There’s no doubt about it that cracked render can be incredibly disappointing and frustrating, especially for homeowners that have just had their houses re-rendered.

As a renderer, it’s important to ensure that all your bases are covered so as to prevent cracking and achieve a long-lasting finish. In today’s post, we’re going to be giving our best installation tips to ensure that cracked render is a thing of the past. 

Prevent Cracked Render with Substrate Absorptivity Tests

The first step in any render installation is to check the absorptive capacity of the substrate. This is an essential step because porous substrates can absorb water out of your render very quickly, which can then affect its adhesion and, you guessed it, cause cracked render. 

The substrate absorptivity test that we recommend is to wet the wall with water and check the rate at which it is absorbed. You don’t want the substrate to be over-saturated with a low absorptive capacity, because this will mean that the render won’t stick, but equally you don’t want it to immediately absorb the water.

If your substrate is highly absorptive, then we recommend lightly dampening the walls with a fine mist of water and then performing the test again. Be careful not to oversaturate the walls. 

Use the Right Primer

Following on from this, a good primer is essential for limiting the absorptive capacity of the substrate, making sure that it is stable and thus preventing cracked render. We recommend using the 301 Water Based Primer, or the EWI-302 Deep Penetrating Primer which is ideal for newbuild brick and blockwork.

A good primer will work to ensure that the substrate doesn’t absorb too much water from your materials. If you use the EWI-310 Universal Primer, then this also contains quartz aggregate which helps to create a mechanical key to aid adhesion.

  • Water based substrate primer
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    Water Based Substrate Primer (EWI-301) – 5 Litres

    £15.23 Excl. VAT
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    Universal Primer (EWI-310) – 20kg

    £49.97 Excl. VAT

Reinforce with Fibreglass Mesh

We recommend the use of Fibreglass Mesh in all of the render systems that we offer. Whether it’s a Monocouche render or a thin coat render system, you can embed the mesh in the first pass or within the basecoat layer. 
Fibreglass Mesh enhances the tensile strength of the render, keeping it nice and sturdy so that it can withstand any movements within the building structure and therefore resist cracking. The mesh is cut into strips and overlapped on all sides so that there are no gaps where cracks can form.

If you want to take the crack resistance up a notch, then we highly recommend using Panzer Mesh within your system, as this is incredibly high strength.

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    Orange Fibreglass Mesh – (EWI-66645) – 50m2

    £46.08 Excl. VAT

Don’t Forget Your Beading

We sell lots of different types of beading, all designed to be embedded within the render to reinforce certain areas. For example, our corner bead help to provide a nice sharp finish at the corners of the render system while also providing this area with reinforcement against impacts. 

The slight difference here is that our thin coat render system beads tend to have a mesh wing to spread the reinforcement across a larger surface area, whereas the scratch render beads have just the hard uPVC without the mesh. 

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    Corner Bead with Drip and Mesh (3mm)

    £4.01 Excl. VAT£5.02 Excl. VAT
  • SALE
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    PVC Stop Bead – Mesh (10mm)

    £3.17 Excl. VAT£3.97 Excl. VAT

Movement Joints

Movement joints need to be reinforced using a render movement bead. These are used where there is a large expanse of render (more than 12m). It’s installed vertically and is embedded within the basecoat layer to stabilise the render and ensure that any cracking is prevented. 

Stress Patches are Essential

Areas above and below openings (around windows and doors) need to be reinforced with strips of Fibreglass Mesh to distribute and resist stresses. The mesh should be cut into strips that extend past the stress patch by at least 50cm. It should be embedded in the middle of the basecoat or the first pass.


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