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Cavity tray installation – how to do it right

Installing a cavity tray correctly is essential for preventing water ingress into a building, particularly at the point where an extension joins an existing structure.

The process is technical and typically requires an expert to carry it out, but a highly skilled DIYer should be able to manage the job, as long as they closely follow the required steps.

Below, we outline how to correctly install a cavity tray.

For best results, we always recommend hiring a professional.

Installing a cavity tray (the correct way)

Follow these steps to ensure your cavity tray is installed correctly:

Step one: Preparation

Before you begin, make sure you understand key information about the wall you’re working with, such as its material, condition and dimensions.

This ensures you select the right type and size of cavity tray and allows you to mitigate against potential risks, leading to a more effective and longer-lasting damp-proofing solution.

Step two: Install the DPC

The first step in the installation process is placing the DPC (Damp Proof Course). Make sure it’s level and continuous along the internal and external skins of the wall.

Overlap the DPC joints to prevent moisture bridging.

Step three: Inner block course

On top of the DPC, start building the inner block course, making sure it’s level.

Check the alignments to make sure everything is aligned and levelled for structural integrity.

Step four: Install the cavity tray

Position the cavity tray so it sits above the inner DPC and extends across the cavity, sloping outwards slightly towards the external wall.

Some cavity trays come pre-shaped with their ends upturned to prevent water from escaping at the sides. If this isn’t the case, turn the ends up yourself.

Step five: Construct the external skin

Lay the first course of bricks on the external side, ensuring the cavity tray slopes down towards it.

Specialists often use engineering bricks, which have low porosity, meaning liquid doesn’t easily pass through, for the course sitting beneath the cavity tray.

Step six: Incorporate weep holes

Position weep holes in the first course above the cavity tray, allowing any water that collects on the tray to easily exit the cavity.

These should be spaced at intervals, usually every two to three bricks.

Ensure these weep holes aren’t obstructed by anything and that they can successfully direct water outwards.

Step seven: Check and adjust

Regularly check the alignment of the wall and adjust as necessary. Also, make sure the cavity remains clear of obstructions and mortar snots.

These checks can help you spot and remove problems early on.

Step eight: Seal and finish

For openings, such as windows and doors, install cavity closers to seal the cavity effectively.

Do a final inspection to make sure all components are in place, with DPC, weep holes, the cavity tray and wall ties are properly installed and functional.

Step nine: Final checks

After you’ve completed the build, check on the wall now and again to ensure there are no signs of moisture or dampness.

If you identify any issues, seek professional advice as soon as possible.

How to get help installing a cavity tray

If you think this process is a bit beyond your skillset, don’t hesitate to call in an expert.

Simply pop your postcode into the search box below and connect with quality bricklayers in your local area.

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