If you’re currently considering beginning a rendering project on your property, you might have heard the terms ‘basecoat’ or ‘adhesive’ crop up. These products are necessary steps in the external wall insulation process. This is because of their ability to secure and seal the layers of the insulation materials, preparing the substrate for rendering.
At EWI Store, we have an extensive range of basecoats and adhesives to suit every project’s needs. For example, some have been designed for use with different substrates, wall structures, and textures.
In this blog, we will take a closer look at the importance of basecoat. We hope to demonstrate that it is an ideal product for every rendering situation. This blog will also discuss the best products, how to go about applying them, and when to use them.
Read on to learn more about basecoats!
What is a basecoat?
Before discussing the importance of basecoats and their various uses, it is worth outlining exactly what it is in relation to external wall insulation.
Basecoats make up a crucial layer of the external wall insulation system. They are a key component in the system as they prepare the surface of the substrate prior to render application.
Our basecoats usually come as a cement-based formula for use as part of a system. There are many different types of basecoats available on the market that can be used for different types of construction projects.
For example, at the EWI store, we have an extensive range of basecoats and adhesives. You can choose from our EWI-225 premium basecoat, EWI-220 EPS basecoat adhesive, EWI-269 Lightweight basecoat, and many more! We will describe some of these products and their various uses in later sections.
Why use basecoat?
As mentioned, this is an extremely useful product to complement render systems. But why should you use it?
The simple answer to this question is that it works perfectly in conjunction with other layers in the external wall insulation system to protect your external walls.
It has long been reported that using a basecoat layer within a render system is a surefire way to provide a long-lasting and crack-free finish for your property.
Not only does it provide a strong and durable base layer for the application of render or insulation materials, but it also improves the overall appearance of the finished project. You can view some installation case studies where basecoat adhesive has been utilised to create an immaculate finish here.
Do you need a basecoat?
Having highlighted the various benefits of using a basecoat, you might be wondering if it is absolutely necessary to use it in EWI installation projects.
The answer is that, while it is not an absolute necessity, it is highly recommended that you make use of it – especially if you want your render system to last. Without applying a basecoat layer, the appearance of the system can be negatively affected – with a ‘ghosting’ effect often occurring when this stage is skipped.
The great thing about basecoat is that it can oftentimes serve a dual purpose. For example:
- You can use it to create a reinforcement layer in render-only or mineral wool, EPS and Kingspan K5 insulation systems.
- You can use it primarily as an adhesive to attach mineral wool insulation boards to a substrate.
The best basecoat?
While all of our basecoats are designed for their own unique purposes, perhaps our strongest and most versatile basecoat is the EWI-225 Premium Basecoat.
Whereas the EWI-220 EPS Basecoat is designed for use with EPS insulation boards and is also a dual-purpose solution, it is not suitable for application directly onto masonry as part of render-only projects. By comparison, the EWI-225 Premium Basecoat is suitable for render-only.
EWI-225 also differs from the others in the range in that it is composed of Portland cement. This premium ingredient delivers a high-strength basecoat consistency. This ensures the surface is prepped with a durable layer prior to the application of thin-coat silicone render.
EWI-225 is EWI Pro’s finest available basecoat adhesive and is compatible with a vast range of insulation materials, including EPS, Mineral Wool, Kingspan K5, Wood Fibre and render-only systems.
We also stock EWI-222p Performance Basecoat, which is a great substitute for Premium Basecoat with many of the same benefits.
Therefore, we highly recommend opting for this basecoat if you’re looking for a highly breathable, flexible and strong reinforcement layer!
When should I use it?
Due to the versatility of this product, it can be applied at several different points throughout the installation process.
When applying it as a reinforcement layer, you should apply it directly to the substrate. You can then follow with a layer of fibreglass mesh which is embedded within the middle of it (at a 6mm thickness).
By comparison, when using it as an adhesive to fix insulation boards to a substrate, you can apply it to the back of the insulation board before fixing it to the substrate.
You can read more about the various installation processes, what you will need, and when to apply certain products by visiting our complete guides page!
How to apply
We highly recommend using a notched trowel to apply our solutions. These come in varying sizes to suit the different qualities of our basecoat range.
For example, we suggest using a 6mm notched trowel when applying EWI-225. This is because it is a finer solution. Whereas you might want to use a 10mm notched trowel for the likes of EWI-220 EPS Basecoat Adhesive.
However, please note that if you are applying our EWI-269 Lightweight Basecoat, a plastering trowel or spray machine should be used to achieve the desired finish.
Source: EWI Pro Youtube
8 thoughts on “The Importance of Basecoat”
can you apply more than one layer of base coat?
Hi Danny, you can apply basecoat in either one or two layers, depending on when you embed the mesh. However, it should not exceed 6mm.
Hi, what basecoat would i use if i want to get a 14 mm thickness.
Thanks, Terry
Hi Terry, we would recommend that the basecoat layer is about 6mm (certainly should not be 14mm thick)
Is a basecoat waterproof when dry? If applied on top of insulation how long can you leave it before you do the silicone render at maximum? I’m wondering since we have a strange project coming up where I might have to wait about 6-9 months with the top silicone render
Hi Andy, as a general rule, basecoats are not waterproof. We do have Aquabase which is usually for installing insulation below the DPC. Regardless, we’d recommend that you procure some rain screens to protect the basecoat if you are having to wait a long time before applying the render.
Our builder has applied the base coat EWI 225 with imbedded fibreglass mesh and has not returned to complete the top coat. How long can this “scratch coat “ be left exposed to the elements before applying the second smooth coat of EWI 225 as a substrate for the thin coat silicone render ?
Hi Paul, the scratch coat really shouldn’t be exposed for longer than a couple of weeks; it has a base level of weather resistance but over time, it can absorb moisture, become brittle, etc. We would recommend contacting the installer to apply the second coat and install some screening if possible.