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Materials Required for Insulating Below the DPC

1. Priming Below the DPC:

If you’re installing your XPS insulation system below the DPC of a brickwork substrate it will need priming with the Water Based Primer. We recommend applying this to the substrate by roller or brush. However, if you are rendering onto a very smooth substrate then we recommend applying the EWI-310 Universal Primer, as this contains aggregates which will provide a rough surface for the basecoat to adhere to. Ensuring that your substrate is adequately prepared is essential to ensuring that your render system will last.

Coverage rates:

5 litres covers 15-30m2 depending on the substrate.

Drying times:

1 coat takes 4 hours to dry.

3. Preparing the Adhesive

Because the DPC area is so prone to damp, we recommend the use of Aquabase as this is a highly water-resistant basecoat/adhesive. Aquabase a very versatile, dual-purpose product that can also be used in the subsequent basecoat layer. The adhesive is applied to the entirety of the back of the board using a notched trowel. 


1 x 25kg bag covers 4/5m2

Drying times: 

24-48 hours

4. Applying the XPS Insulation Boards

XPS insulation boards are ideal for below the DPC because they offer a closed-cell structure which makes them more waterproof and impact-resistant. We sell XPS by the square metre in a range of thicknesses. For insulating a solid brick wall the general recommendation to reach building regulations is to opt for a 110mm thickness. A really flat surface will need to be achieved while mounting the boards to ensure a smooth topcoat. We recommend using a spirit level to regularly check that everything is flat. 



5. Installing the fixings

EWI Pro recommends that you install one fixing per corner, with an additional two in the middle of the insulation board. Plastic fixings should be used with the XPS insulation system as they significantly reduce thermal bridging. The fixings are available in a wide range of lengths to accommodate different thicknesses of insulation.


Plastic pin fixings are the recommended fixing for XPS insulation. These come in boxes of 200 or 100 depending on the length.

6. Applying the Beading:

Beading is essential for reinforcing external areas that are more prone to damage, for example, the corners and the areas around windows and doors. The required beads will depend on the property and which particular areas need reinforcing. We have a broad range of render beads that should be selected and applied as necessary, our beads are uPVC and are designed to be embedded within the basecoat layer. For real security against condensation and cold spots, you may also want to use a foam tape in between the starter track and the top of the insulation boards.

7. Applying the Basecoat:

For insulating below the DPC with XPS insulation, we recommend using the EWI-226 Aquabase in the basecoat layer again for added protection against damp and water penetration. 

Coverage rates:

1 x 25kg bag covers 4/5m2

Drying times:

24-48 hours

8. Priming the Basecoat:

A render primer should be used to increase the adhesion of the render to the basecoat and can be tinted to match the colour of your render for increased opacity. The type of primer will depend on the type of render you are using. When using Mosaic Render, we recommend using the Mineral & Acrylic Primer which comes in two different bucket sizes.  


1 x 7L bucket covers 20m2

1 x 21L bucket covers 60-70m2

Drying times:

12-24 hours

10. Applying the Render Topcoat:

Once the primer is dry, the render topcoat can be applied. We recommend using the EWI-050 Mosaic Render as this is very durable and waterproof, which makes it perfect for below the DPC. Mosaic Render is available in a range of colours to achieve a unique finish. 


1x25kg bucket covers c. 3-4m2

Drying times:

24 hours (+)

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    One thought on “Materials Required for Insulating Below the DPC

    1. We’re replacing a cement plinth around the base of a brick house. It was bridging the dpc but didn’t seem to be an issue. Should we put the bead in. Might look odd as is only 50cm of render?

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