Scotland tends to have the harshest climate in the British Isles because it is the furthest northerly region. In the winter the northerly winds and the chill factor make the region a cold place to live and therefore the heating requirements are a lot greater than southeast England. Also Scotland seasonally is a lot wetter throughout the year, therefore the impact on building wear and tear is quite significant. It becomes quite essential to look after properties, especially protecting the external envelope – the walls and roof so they are robust enough to deal with all these factors.
Up to now the render of choice for many properties has been pebble dash or thick coat renders – this is because over the years they have had a perceived reputation for keeping the properties protected. However recently thin coat renders have started to become a lot more popular in the UK and their introduction in Scotland makes a lot of sense.
What is a thin coat render system?
A thin coat render system consists of a fibre glass mesh sunk into a “thin” layer of adhesive onto the wall. The system is then finished off with a thin layer of grained or scratch render. If you are applying this to block or brick work then you are talking about at most 1cm layer of thin coat render (the render is actually only 1.5mm of this!) opposed to 3-5cm for your traditional thick coat render systems.
The thin coat renders don’t actually stop there – they can be used in conjunction with expanded polystyrene or mineral wool insulation (which sits underneath the render) – this not only provides the property with the benefits of a render system but also this process is actually upgrading the thermal properties as well.
What are the advantages of actually using thin coat renders?
Thin coat render systems have many advantages over traditional renders and some of these are explored in the following section:
Uses less material vs. traditional renders
Thin coat renders use less material than thick coat renders therefore in theory can cost less to apply to the walls. Given that traditional renders tend to have a thicker finish they tend to burn up more materials on the job. Also traditional renders may require multiple coats, which means they can use up to 3 times more material volume than thin coat renders.
Using more material is not a problem but it can become an issue if you are quite away from the big cities of Glasgow and Edinburgh and supplies are hard to replenish. If you require less materials (e.g. thin coat renders) on a job you are essentially more mobile and can budget for additional slack to cover you should you need more meterage on the job.
If you are installing a silicone top coat with the thin coat render the finish will be flexible. Whether you are using the full silicone system, the silicone silicate or the nano silicone finishes these top coats all provide a very flexible finished surface. You can see this demonstrated by simply applying any of these renders to a thin piece of expanded polystyrene (EPS) board. When the board is dried you can then hold both of the edges and bend the EPS board quite a way without it snapping on.
The underlying flexibility however also comes from the fibre glass mesh, which is installed before the top coat is applied. The fibre glass is very flexible and this allows the system to move and stretch without cracking. Traditional sand and cement renders don’t contain this fibre glass mesh layers, which means when they are exposed to normal conditions can crack relatively easily.
Saving time in the installation process
Traditional renders may require multiple coats whereas thin coat renders actually only have one top coat therefore the process tends to be a lot less labour intensive. Experienced installers can usually managed 2-3 projects at the same time if they are using thin coat render products.
Although thin coat renders can be applied to the walls quickly and efficiently, the fitter needs to pay close attention to the drying times, especially the drying of the basecoat layer. If the basecoat layer is damp underneath then the top coat finish may not come out as expected. For example the render may not stick to the wall or worse when fully dried the finish may look stained and patchy.
The best thing to do is to consult the manufacturers specifications and pay close attention to the allotted drying times. Most manufacturers stipulate 48-72 hours for the basecoat (mesh layer) to dry before preparing the walls for the finishing layer – however at the end of the day if you are an experienced fitter then you will know best.
For example if you are installing a thin coat render system in Inverness in the spring you may find the atmospheric conditions to be wet and humid. In this case you may find the surface of the basecoat (fibre glass layer) to be dry but under the skin it could still be damp and not ready for the top coat. In this case you can make tiny test incisions and just get a feel for how it is. If it is dry then process to the final coat.
Can be installed in harsh environmental conditions
Thin coat renders can be installed with silicone, mineral or acrylic top coat finishes. We fully endorse the silicone and mineral systems, but discourage the acrylic systems due to their lack of breathability.
If you have ever used a silicone based system in the autumn on a property and you have been unlucky with the wet weather, then you may have unfortunately encountered a wash off. This is where it rains and the silicone render hasn’t dried properly, meaning the render simply washes off the wall and has to be applied again.
Mineral render finish doesn’t have this issue, because it dries mechanically as oppose to via moisture dispersion in the silicone render. When the climate is damp and humid, the mineral render works very well – drying quickly and reducing the risk of wash offs.
The only disadvantage of the mineral system is that it has to be sealed with a layer of silicone paint on top. However as this layer is only 0.05mm it dries as quickly as the mineral render underneath it, therefore reducing the risk of it washing off.
Accelerators can be mixed into silicone renders to set them off quicker in the winter months, however we don’t recommend this and prefer if installer use the mineral render system.
A range of finishes
With thin coat renders you are not limited to a few finishes – you can have the grained or the scratched finish. The grained finishes come in different sizes – so if you want to imitate the traditional sand and cement “smooth” look, you can have 1.0mm render installed. Otherwise the 1.5mm grained coloured render is the most popular thin coat render finish in Scotland.
Thin coat renders can be pre-mixed with 100s of different colours, so if you are set on matching the look you had previously on your home it is pretty easy to get like-for-like finish.
Finally, most thin coat render systems are compatible with the installation of external features, such as external mouldings or brick slips. However always check with the manufacturer first to ensure the loads on the system are taken into account to accept the heavy features.
The silicone and mineral thin coat render systems are breathable, which means they are very good for dissipating moisture and dirt debris that can build up over time. Over time the walls can be cleaned off with a low powered jet-wash, and if they are maintained properly then they should require very little maintenance.