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The Best Primers for Rendering?

You wouldn’t bake a cake without greasing the tin, in the same way that you wouldn’t install EWI or render without first applying a primer. Priming isn’t really something that is spoken a lot about with regards to rendering, yet nevertheless it’s an important step in the process to ensure good adhesion of materials and a long-lasting finish.

Here at EWI store, we offer a range of different primers for different purposes and products, and often customers struggle to understand which primers are required for their particular property. In this blog post we hope to set out the difference between each of our primers, and explain their purposes; so keep reading to find out more!

Substrate Primers

Substrate Primers are as the name suggests. They are used to prime the wall before anything is applied to it. This is the very first step in a rendering or EWI Process, and often the substrate primer that you choose will depend upon the absorptivity and the type of substrate that you are applying the basecoat onto.

EWI-301 Water Based Primer

The EWI-301 Water Based Primer is used to limit the absorptivity of a substrate. Over-absorption can have a damaging effect on EWI systems because it can affect the structural integrity of the materials. The EWI-301 is therefore used on an as-needed basis and applied directly to the substrate prior to anything else; it will basically prevent too much water from being absorbed from the basecoat. It can be applied to walls made of bricks, blocks, aerated concrete, structural clay tiles, gypsum plasterboards, gypsum panels and plaster coats.

EWI-310 Universal Primer

The EWI-310 Universal Primer is a particularly great primer if you have a smooth substrate, i.e. concrete. It limits absorption by the substrate and the presence of quartz aggregate within the primer helps to create an artificial key, facilitating adhesion and application of basecoats and adhesives… one of its ‘key’ benefits if you see what I’m saying. Another one of the great things about the EWI-310 Universal Primer is that it helpfully dries red on the wall so that you can see where you’ve already applied it – therefore limiting over-application, saving you money by making the product go further!

Render Primers

Render Primers are applied directly onto the basecoat before application of the render itself. Choosing your render primer will depend upon the type of render that you are about to apply. We have a range of render primers that are suitable for use with our entire render range.

EWI-330 Mineral Acrylic Primer

The Mineral Acrylic Primer is used as means of final preparation before you apply your render. This basically means that it is applied on top of the basecoat/adhesive before you render. The EWI-330 is specifically designed for use with our Mineral, Acrylic and Mosaic renders, and it can be tinted to match the colour of the render for strong opacity. EWI-330 comes in both 7kg and 21kg tubs so you can purchase the right size for your particular requirements.

EWI-333 SiSi (Silicone Silicate) Primer

Much like the EWI-330, the EWI-333 SiSi render primer is applied to the basecoat/bedding adhesive as a means of final preparation before render application. It’s ready to use and comes in 21kg and 7kg tubs; designed for use with the EWI-075 Silicone render or the EWI-040 Silicone Silicate render. This primer can also be tinted to match the colour of the render that you are going to be applying for strong opacity and a uniform finish.


Worth mentioning, the Fungicidal Wash and Render Accelerator are additional steps that an installer may decide to take as best practice depending upon the situation.

Fungicidal Wash

Fungicidal Wash is a proven biocide and is used to clear the substrate of any kind of moss or growth before you do anything. It needs to be applied 24 hours prior to applying anything else to the substrate, after which time it should have killed off all organic growth.

Render Accelerator

TheRender Accelerator is designed to be added to your render in order to speed up the drying process. It’s a liquid additive which is perfect for use when the weather is more damp or cold – many of our installers have raved about how much time the Render Accelerator has saved them when rendering in unpredictable weather.

So there you have it! Hopefully this will enable correct decision making over which primers are required for different jobs. Usually our sales representatives would be able to advise you if you are placing an order over the phone, however it’s always good to be well informed and prepared ahead of making your purchase. We upload to our blog every Tuesday and Thursday, answering frequently asked customer questions and tackling some of the technical problems faced when installing EWI in different circumstances. So don’t forget to stay tuned for more and follow us on social media for updates and exclusive offers!


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