Which Insulation Adhesive Do I Use?

There are several rules to follow when installing external wall insulation, one of which is always to use the correct insulation adhesive. At EWI Store we offer a range of EWI Pro insulation adhesives, all of which are designed for use with different insulation boards.

In today’s post, we are going to be talking you through the different insulation adhesives within the range, including which ones should be used for which insulation material.

What is a basecoat adhesive?

Basecoat adhesive in terms of External Wall Insulation (EWI) systems, also known as External Thermal Insulation Composite Systems (ETICS), is a key component that serves several important functions:

1. Adhesion: As the name implies, basecoat adhesive is used to bond the insulation boards (usually made from materials such as expanded or extruded polystyrene or mineral wool) to the exterior surface of the wall. This layer also ensures that the insulation boards stay firmly attached to the wall.
2. Levelling and reinforcement: The basecoat adhesive is also applied over the top of the insulation boards. A layer of reinforcing mesh (usually made of fibreglass) is then embedded into the wet basecoat. Once the basecoat hardens, this provides a strong, reinforced layer that helps protect the insulation boards from mechanical damage.
3. Weather protection: The basecoat adhesive layer can provide a degree of weather resistance. It helps to shield the insulation boards from direct exposure to moisture, which can degrade their thermal performance and durability.

The basecoat adhesive is usually a cementitious or polymer-modified compound, designed to provide strong adhesion and good resistance to weathering and mechanical damage. The exact formulation of the adhesive can vary depending on the specific requirements of the EWI system and the type of insulation boards being used.

After the basecoat adhesive layer has been applied and cured, it is usually covered with a decorative and weather-resistant finish coat or topcoat. This provides further protection against the elements and gives the final aesthetic appearance to the wall.

EWI-222P Performance Basecoat

EWI-222P Performance Basecoat is a polymer-rich cementitious basecoat that can be used on many different substrates, providing a breathable and water-repellent protective coat. You can use EWI-222P on render-only projects as well as on EPS (where it can be used as an adhesive and a basecoat). As such, it also reduces wastage as only one bag is required on site. EWI-222P should always be finished with a Silicone Render to ensure a robust and long-lasting decorative finish.

EWI-220 EPS Basecoat

As the name suggests, this type of insulation adhesive is designed for use with our EPS insulation. It can also be used for XPS. Because EPS is such a lightweight insulation board, it does not require as much of a heavy-duty adhesive as other materials.

The EWI-220 creates a strong, long-lasting adhesion, securing the boards to the substrate for years to come. It can also be used within the basecoat reinforcement layer, whereby a Fibreglass Mesh is embedded within the adhesive. The purpose of this is to create a smooth, strong surface ready for the render to be applied to. 

EWI-225 Premium Basecoat

The Premium Basecoat is our strongest adhesive, designed for securing Mineral Wool, Wood Fibre and Kingspan K5 insulation boards to substrates. This particular adhesive contains Portland cement and fibres which create a highly adhesive material. This also makes it able to support the weight of these heavier insulation boards.

Like the EWI-220, this insulation adhesive can also be used within the basecoat reinforcement layer. Because the product is so strong, it’s also ideal for use in the basecoat layer for render-only systems.

EWI-221 Winter Adhesive

If you’re installing EWI during the winter months, then you may want to consider using our EWI-221 Winter Adhesive. This insulation adhesive can be used for EPS and XPS, at temperatures even down to zero degrees.

Filling gaps between insulation boards

If you’re installing external wall insulation, you may find that you end up with small gaps between the insulation boards. The best way to sort this is by either using insulation offcuts, which is probably ideal for larger gaps or by using a spray foam adhesive.

Gaps between boards should never be filled using adhesives. This is because spray foam adhesives are best for preventing thermal bridging, as they have a low thermal conductivity. Insulation adhesives will just let all the heat escape through the gaps and cracks.

Thermal bridging can lead to several problems:

1. Increased Energy Loss: If heat can escape more easily, your building will be less energy efficient. This means you may need to use more energy to maintain a comfortable indoor temperature. As a result, bills can rise.
2. Cold Spots: Areas around thermal bridges can be noticeably colder in the winter, or alternatively, hotter in the summer. Ultimately, this causes discomfort and inconsistent temperatures throughout the building.
3. Condensation and Moisture Problems: Thermal bridges can lead to surface condensation, as they can create cold spots where warm, moist indoor air can condense. Over time, this can lead to moisture problems, including mould and structural damage.

Filling gaps between insulation boards and ensuring a continuous layer of insulation is crucial for preventing thermal bridging. This is why any gaps between boards are usually filled with more insulation. Alternatively, it can be filled with a suitable adhesive or sealant, and why the seams are also sealed with tape or covered with a basecoat adhesive and reinforcement layer in external wall insulation systems.