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How to fix Mineral Wool to Sheathing Board

Fixing Mineral Wool to sheathing board, or even insulating sheathing board in general can be a bit tricky. Ventilated cavities or no ventilated cavities? Render carrier board onto battens or no render carrier board onto battens? The list of options goes on, hence why so many people seem to avoid working with these systems.

Well, at EWI Store we’re going to tackle the subject and make it nice and easy; if you’re going to be insulating a sheathing board substrate then the easiest thing to do is stick some Mineral Wool on and render over it. So without further ado here’s our how-to guide…

Preparing the Sheathing Board

Whether it’s a timber frame or a steel frame, the sheathing board needs to be a prepared in the same way. It’s imperative to use a joint tape to secure all the joints between the sheathing boards together; this essentially improves how weathertight the system is and protects against condensation gathering between the gaps.

We recommend using a breathable joint tape such as the Pavatex ‘Pavafix Win’ tape; this is a self-adhesive breather membrane that is incredibly easy to apply.

Sheathing board typically doesn’t need priming, so you are free to skip this stage altogether and go straight to fixing the Mineral Wool insulation.

Fixing the Mineral Wool to the Sheathing Board

When insulating directly onto sheathing board, the EWI-225 Premium Basecoat should be used. This can be applied to the back of the insulation boards to secure them to the substrate, then stainless steel self-drilling screws with universal fixing discs should be used as a secondary method of securing the insulation.

Applying Render to the Insulated Sheathing Board

Rendering the Mineral Wool involves applying a basecoat layer of the Premium Basecoat to the insulation boards, before embedding strips of fibreglass mesh within the basecoat. Don’t forget that each strip of mesh should overlap by 10cm!

The basecoat needs to be left to dry, and then it should be primed with the appropriate render primer – for example, you’d use our Top coat Primers with our Silicone Silicate render, so whatever render you are using the primer should match.

Once the primer has dried, you are then ready to render. Apply your render of choice to the substrate using a plastering trowel; if you are using our thin coat renders then the thickness that the render is meant to applied at should match the grain size you have chosen.

And there you have it! Applying Mineral Wool to sheathing board is a really easy way to not only get the render finish that you want, but also improve the thermal performance of the whole building structure.

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