ecoCORK Insulating Render

Secil ecoCORK has a lambda (k) value of 0.1 and offers a thermal improvement compared to a traditional lime render.

It was decided that the hard cement render should be removed and replaced with an insulating lime render made with cork as the aggregate. Secil ecoCORK is free from cement, is lightweight and offers extra insulation value to a building that has a poor Lambda value being made from subsoil.

When the cement render was hacked off, it was clear that the walls had been kept very wet due to the wrong materials being used. Many of the timber lintels had to be replaced and when a wall is damp, it is a poor insulator, so successive residents would have had to endure a colder home and higher heating bills.

It is important when doing this type of building work that the correct health and safety is observed as well as informing all the necessary regulator authorities for the correct permissions.

This cob cottage has a wide range of different materials that have been used throughout its history:

• the original stone was bed in an earth mortar,
• the lintels are oak,
• the roof level has been raised by adding hard concrete blocks and,
• the same type of concrete blocks have been used to infill alterations to doors and windows.
• Old soft bricks had been used previously to face certain parts of the elevation.

The wide range of building materials is not unusual but is far from ideal. It is important to consider the mantra ‘like for like’ when considering what materials to use when undertaking maintenance or improvements to any building. Understand the issues these materials bring – an experienced builder will understand how best to minimise problems.

For larger quantities, we tend to mix the Secil Reabilita Cal CS in a rotary drum mixer first as this can be mixing as other work is carried out. After approximately 15 minutes, transfer the mix to a bucket, add further water and whisk with a drill attachment.

The whole point of harling a splatter dash (scat) coat of consolidation mortar on to a wall is that it bonds very well with the substrate as well as firming the wall and offering a good physical key to the Secil ecoCORK. The Consolidation Mortar, as with any harled coat, should be applied with a firm flick of the wrist. A tyrolean flicker gun will not give sufficient power and bond to hold the next coats of render. 

Wear the correct protective clothing as even the professionals don’t always get all the mortar on the wall! It is not strictly necessary to totally cover the substrate but a good covering of at least 95% is ideal. Remember that this coat is simply to consolidate the surface, provide a good key and to control suction.

A scat should be allowed to harden before applying the next coat so that it remains solid as the ecoCORK is laid on. Consolidation mortar sets faster than a lime putty based mortar and only requires 24 hours before ecoCORK can be applied.

If wooden lintels are to be covered by the render, consider the best way to attach the render. In this case we chose a tried and trusted method of counter battening, lath and haired lime mortar. In this case, we also used a fibre glass mesh to help reduce the chances of stress cracks.

Cork it is not only insulating but also lightweight and therefore offers lower shear stresses on the substrate. Apart from the added insulation value, the eco-credential for using cork instead of sand should make this product high on the list of anyone looking for an environmentally sensitive render. You or your plasterer will appreciate the reduced stress on the body due to reduced weight as well!

Application

ecoCORK is supplied as a dry premixed mortar, so simply open the bag, add water and place in the mixer. The mortar should be allowed to absorb the water for approximately one hour before application.

Apply ecoCORK in 10-20 mm layers up to a maximum of 40 mm.

Protect your work from rain, sun, wind and frost whenever necessary. Cover the newly applied render with hessian or similar to protect and control drying. All lime mortars must remain damp for at least 72 hours after application.

It is important both to consolidate the render and to provide adequate key for any subsequent coats. Use wooden floats to open the texture nicely and allow plenty of pressure to compact the render. Compacting is important because, as the water leaves the newly applied lime mortar, the volume reduces and can cause shrinkage cracks.

One or two very thin coats of Secil Reabilita Cal AC should be applied and finished as desired with a sponge or trowel. A sponged finish will remove trowel marks and open the texture to allow a good bond with suitable, breathable paint.

Decoration

This building was decorated with Silicate Masonry Paint colour matched to our own Parchment Limewash Colour.