Secil ecoCORK with a lambda (k) value of 0.1, offers an improvement of perhaps 8 x times the insulation value of traditional lime render mixed with sand.
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 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. It is important to understand the issues these materials bring and an experienced builder will understand how best to minimise the problems.
For larger quantities, we tend to mix the Secil Consolidation mortar in a rotary drum mixer first as this can be mixing as other work is carried out. After approximately 15 minutes, the consolidation mortar mix can be transferred to a bucket, further water added and then whisked 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. If a drier mix normally used when rendering is applied by a laying on trowel, it will never achieve such a good bond with the substrate. 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. This equipment, if deemed appropriate should only be used as a final finish. Be sure to 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 lime mortar coat is simply to consolidate the surface, provide a good key and to even out and 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 there are wooden lintels to be covered by the lime render, you need to consider the best way to fix the mortar. In this case we chose a tried and trusted method of counter battening, lath and haired lime mortar. In this case we also employed a flexible fibre glass mesh as this helps to reduce the chances of stress cracking and cracking due to movement caused by the differential with varying materials. We like to use this across junctions of concrete block and stone or cob as this is always a potential problem created by the excessive thermal coefficient between the natural and modern building materials.
As the aggregate used is cork it is not only insulating but also lightweight and therefore offers lower shear stresses on the substrate making it ideal for cob and straw bale. 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 material to render with. You or your plasterer will appreciate the reduced stress on the body due to reduced weight as well.
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 an hour before application, so be sure to allow sufficient time for mixing and standing.
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. It is good practice to cover the newly applied render with hessian or similar to maintain the mortar in a damp state. All lime mortars must remain damp for at least 72 hours after application.
As with all plastering and rendering, it is important both to consolidate the render and to provide adequate key for any subsequent applications. We tend to use wooden floats as these open the texture nicely as well as allowing plenty of pressure to compress the mortar. Compressing the mortar is important because as the water leaves the newly applied lime mortar, the volume reduces and can cause shrinkage cracks and, in extreme cases, causes the mortar to pull away from the substrate.
One or two very thin coats of Secil Finishing Render 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 subsequent decoration by a vapour permeable paint.
This building was decorated with Earthborn Silicate Masonry Paint colour matched to our own Parchment limewash colour.