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What Do Substrate Primers Do?

Substrate primers are an essential part of the installation process of EWI systems. Substrates vary on site and all require preparation. There are various stages to preparation, and our range of primers can prepare all manners of substrates and basecoat layers. In this blog, we are going to discuss our range of primers and how they affect your project.

Preparing your substrate

The first step of renovating any wall is preparation. You must examine the wall for any defects, and potentially level the surface. We do offer a solution in the form of our Levelling Mortar. Using a trowel, you can repair holes and other imperfections, up to a depth of 50mm. Much like a lot of our products, the EWI-260 is versatile and you can repair a vast range of substrates.

Our primers come into play once the surface of the substrate has been repaired. At EWI Store, we offer four different types of mixtures that prepare your substrate in different ways.

Fungicidal Wash is a preparatory product for cleaning walls, block paving, and normal paved areas. The purpose of the wash is to kill mould, algae, lichen, and mildew, which is essential for the health of your walls. Biological growth can disrupt the structural integrity of walls if left unchecked. On timber frame structures, the biological growth can lead to rot due to allowing damp to penetrate the walls. Whilst not explicitly a substrate primer, the Fungicidal Wash plays a crucial part in the preparation of your substrates. The wash will also prevent the regrowth of microorganisms for 6 months.

Substrate primers

The primers to use following the washing stage are either the Water Based Substrate Primer, Universal Primer, or the Deep Penetrating Primer. They share many similar benefits, with a few distinct properties which may make them more suitable for your project.

Water Based Substrate PrimerEWI-301 Water Based Primer prepares the wall before installing external wall insulation or render-only systems. Water Based Primer dries completely colourless and limits the absorptive capacity of the substrate, while simultaneously strengthening and stabilising dusty substrates. It also provides enhanced adhesion for the application of paint or render coats, helping to ensure a long-lasting finish. As with most primers, it regulates the groundwork absorbency.

Universal Primer EWI-310 Universal Primer prepares the walls before the application of our adhesives. It improves adhesion of the adhesive to the substrate, facilitating application and reducing groundwork absorbency. Universal Primer is easy to apply and distinguish on the substrate as it is tinted red. The presence of quartz aggregate in the primer creates a strong textured surface onto which the adhesive layer can bind easily.

Deep Penetrating PrimerEWI-302 Deep Penetrating Primer is a preparation primer for external walls. It is ideal for use on highly absorptive surfaces, as it works to consolidate and strengthen the substrate while limiting its absorptive capacity. Deep Penetrating primer is easy to apply, dries completely colourless and will facilitate the application of render and external wall insulation products.

A wall with Universal Primer applied
A wall with Universal Primer applied

Priming before rendering

The process of priming before rendering is similar to substrate priming. Primers are applied using either a brush or a roller to achieve a consistent surface that has boosted adhesion to the topcoat layer.

Topcoat PrimerEWI-333 Topcoat Primer is specifically designed to work with our range of silicone renders. There are several reasons for using the Top Coat Primer (EWI-333); firstly it aids adhesion between the render and the basecoat. Secondly it limits the absorption of the basecoat layer, ensuring the render cures properly – this is especially important during the summer months, giving the installer time to get a finish on the render. Finally, the Top Coat Primer can be tinted in the same colour as the render, ensuring that there is no basecoat bleed through. 

Mineral & Acrylic Primer EWI-330 Mineral & Acrylic Primer is designed for the final preparation of a basecoat surface before the application of EWI Store Mineral, Acrylic, and Mosaic Renders. The primer strengthens the substrate and balances the absorptive capacity, whilst maintaining the breathability of the whole system. As with the Topcoat Primer, EWI-330 can be tinted to match the render, avoiding bleed through from the basecoat.

  • Universal Primer EWI-310
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    Universal Primer (EWI-310) – 20kg

    £60.03 Excl. VAT
  • Top Coat Primer (EWI-333)- 20kg

    From £65.81 Excl. VAT
  • Deep Penetrating Primer EWI-302
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    Deep Penetrating Primer (EWI-302) – 5 Litres

    £20.99 Excl. VAT
  • Water Based Substrate Primer EWI-302
    Quick View

    Water Based Substrate Primer (EWI-301) – 5 Litres

    £15.74 Excl. VAT
  • Quick View

    Mineral & Acrylic Primer (EWI-330) – 20kg

    £58.41 Excl. VAT

The properties that tie all of our primers together is the fact that they are waterproof and frost-proof, whilst retaining their vapour permeable properties. This contributes to the vapour permeability of our system build ups, and is crucial to preventing condensation within properties.

What else should you consider?

A product that aligns with the preparation of products and substrates is our Render Accelerator. Render can have issues with drying times when the temperatures drop lower. The addition of Render Accelerator (100ml per 25kg bucket) can cut curing and drying times in half. The product has no effect on the final render finish as it does not affect the consistency or colour.

You can learn all about our primers and how to use them at our partner’s Training Academy.


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