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Using Expanding Foam Tape in an EWI System

Having recently started stocking Expanding Foam Tape as a part of our EWI materials line-up, we’ve been speaking to a lot of installers and customers about the benefits of using Expanding Foam Tape as a sealant within an external wall insulation system.

If you are a regular reader, or you’re familiar with external wall insulation, then you will know that moisture and water vapour can be detrimental to the way that the EWI system performs. The presence of water can decrease the insulation system’s ability to insulate by a shocking 50%. As well as this, water can enter the system and freeze causing damage to the render and the insulation boards. Therefore, ensuring that your EWI system is totally sealed (especially at weak junctures) is really important.

So, in what instances can I use Expanding Foam Tape when installing EWI? We wanted to explain a couple of situations where Expanding Foam Tape can play a really useful and important role as part of an external wall insulation system.

Using Expanding Foam Tape for EWI and Window Joints

A good example of when you may need to use Expanding Foam Tape in an EWI system is around windows – particularly window sills. For example, if you are installing EPS onto a building then you are going to need to install the EPS so that it tucks right up underneath the window sills.

Areas where the EPS terminates against other building components (e.g. window sills) will need sealing with tape. As we know, buildings expand and contract during heating and cooling. Therefore, during this expansion/contraction, areas where the EPS is in direct contact with the window sill can form exposed cracks where the weather can penetrate, and moisture can build up.

Installing Expanding Foam Tape in an EWI system as a joint sealant is a very effective way of preventing moisture build-up, as the foam will accommodate the impact of the continual minute movements of the building by expanding and contracting with the building components, therefore providing a waterproof seal.

Using Expanding Foam Tape for EWI and Verge Trim

Verge trims are great for capping over the top of your insulation system where the roof line does not fully extend out enough to cover the EWI system and protect it from the elements. Verge trim is installed over the top of the insulation, redirecting water down the water-proofed side of the external wall insulation. When installing verge trims, you would need to apply the Expanding Foam Tape to the top edge of the insulation material (e.g. EPS) in order for it to expand and fill the gap in between where the insulation meets the underside of the verge trim.

The top edge of the insulation is a very vulnerable area in terms of being exposed to the elements. The verge trim therefore acts as a shield so that water will run off the side of the EPS, rather than seeping down the back. However, it’s important to ensure that no moisture can build up in between the two components as this would eventually cause damage and detriment to the system, so therefore sealing the area with Expanding Foam Tape is really important.

Top tips for installing Expanding Foam Tape in an EWI system

  • Ensure that the area of application is clean, dry and dust free so as to allow for optimal adhesion.
  • When installing in hard to reach places, use a spatula to press down on and secure the tape.
  • The joint will close as the foam expands, however in colder temperatures this will be significantly slower.
  • Never install around a corner – instead form a butt joint and overlap the tape at both ends.
  • When starting a new strip of tape mid-way along a joint, overlap the strips from end to end.
  • Always cut off extra tape (around 10mm per metre) to allow for any recovery of stretching that may have occurred during installation.
  • For best results, ensure that level changes of cracks/joints are as small as possible.
  • For joints of changing width, use tape of different widths and overlap the ends.



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