One of the biggest issues with old sand and cement renders is that over time they crack. The cracks may start small but before long they can really ruin the look of your home – and they can also lead to water ingress.
Because thin coat renders are a fairly new trend when it comes to rendering, it’s more common that properties have an existing sand and cement render. As you will know if you’ve read our blog ‘Sand and Cement Render vs. Thin Coat Render Systems,’ thin coat render systems are much more flexible and are far less likely to crack than a sand and cement render. This is because our thin coat render systems are comprised of a flexible basecoat which has fibreglass mesh embedded within it for extra tensile strength and crack resistance, then a thin coat render is applied on top of this smooth basecoat. The render is called a thin coat render because, as the name suggests, it’s applied in an extremely thin layer of around 1-3mm thick (depending upon the grain size you go for and therefore the type of texture that you want to achieve). We would always recommend using this system going forward, as sand and cement renders are just unreliable in comparison.
For those who have had sand and cement render previously installed, we get a lot of people asking us what the best solution is to fix the cracked render. Well, you have a few choices, depending on the severity and size of the crack as well as how long it has been there:
1. Fixing completely blown render across the entire property
If the render is falling off the walls everywhere you have two options:
The best solution for fixing cracked render is to start again! It’s probably not what you want to read, but putting any other materials on top of cracked render is akin to adding a plaster – it is only really a temporary fix and it’s likely that over time the cracks will just keep expanding and getting worse. We would therefore always recommend removing the existing render back to the brick work, but we appreciate many people won’t want to do this due to the time and cost involved.
Fix render by adding a thin layer of EPS insulation
The next best solution is adding a thin layer of insulation (20mm or 30mm) to the wall – this needs to be attached to the wall with adhesive and anchored to the wall using mechanical fixings. Prior to adding the insulation board, do try to remove any very loose render and make good the surface with Levelling Mortar (EWI-260).
Once the insulation boards are in place, and the adhesive holding them to the wall has set, then you carry on the rest of the system as normal. On top of the insulation boards, a 6mm basecoat layer should be installed (with reinforcing fibreglass mesh embedded within it), and a thin coat render finish should be applied on top to create a decorative finish. Read our blog ‘coloured render cost per m2‘ for more information on how much this render system typically costs by the square metre.
Applying a thin layer of EPS essentially means that you are creating a new, stable substrate onto which you can apply the thin coat render system. It also means that you will boost the thermal performance of your home, albeit this is relative to the thickness of the layer of insulation.
2. Fixing cracked render on one panel of wall
If there is just one area of the wall that is cracked, then we recommend filling the crack with our Levelling Mortar and then applying a fresh layer of basecoat and render to just that panel (i.e. a square house would have 4 panels, front back and 2 sides). Hopefully the panel in which the crack has occurred isn’t the whole side of the house, and there is a natural break, for example a downpipe, which can disguise where the new render meets the old render.
By installing a new layer of basecoat and then re-rendering the entire panel, it should ensure that the cracked render does not crack again in future. The flexibility of the base coat, combined with the flexibility of the render top coat, should provide a crack-free solution.
3. Fixing a very small crack or area of impact damage
There are some cases where a very small crack has occurred that needs fixing; for example maybe a bin has blown against the wall, or a car has ‘gently’ reversed into it. In this situation you have a couple of options. Firstly, you can remove a square of render around the affected area and basecoat and render this area. This involves taking an angle grinder and trying to remove a clean square around the impacted area.
Unfortunately, there will always be an issue of scarring where the new render meets the old render. This is a consequence of the fact that the render is so thin – there is simply no way the two sections can be blended together without visible scarring. The square (marked out using rendering tape) ensures that despite any scarring being visible it is still neat.
The other solution for sorting a small crack in the render is to basecoat the whole panel and re-render the property – again a bit more work but you won’t be able to see where the original crack in the render was, therefore it gives a nicer finish than marking out the square (as described above).
We often get people ordering additional buckets of render to make repairs on cracked/damaged render and they simply ‘touch up’ the affected area, but 99% of the time this will result in unsightly visible scarring. We would always recommend following one of the methods described above.
Which thin coat render should I go for?
There are four options that you can choose for thin coat coloured renders:
- Silicone render: Silicone Coloured Render is a premium, modern technology coloured render – which is available in hundreds of different colours. Silicone is a very popular choice because it offers hydrophobic properties, which means that it repels water, dirt and organic growth – so it requires very little maintenance. Silicone render is also super easy to apply because it comes ready to use, so you just apply it straight out the box. (Read more about Silicone Render here).
- Silicone Silicate Render: Silicone Silicate Render is our most popular hybrid-silicone render. Silicone Silicate Render is our best value render, offering the key benefits of a thin coat render as well as the breathability and vapour permeability that the silicone provides. Silicone Silicate also provides an element of self-cleaning capabilities. This is a great render if performance and functionality at a great price point are key priorities.
- Acrylic render: Acrylic Coloured render is very similar to silicone, except for it doesn’t provide the same breathability. It’s a solid middle-ground thin coat render because it still provides the same flexibility, Acrylic render is also great at holding onto colour pigment. So this is also a fantastic choice if you are looking to fix cracked render. (Read more about Acrylic Render here).
- Mineral render: Mineral Coloured render is a dry-mix, thin coat render. This is a very popular choice if you live in a cold or rainy climate because mineral render is extremely fast drying (you can’t apply other renders in cold/rainy temperatures because they take longer to dry). The only thing about this render is that you need to paint it afterwards with silicone paint to seal it in. This is because if it’s left exposed to the elements it can develop lime bloom due to the presence of Portland cement. (read more about Mineral Render here).
At EWI Store, we are very happy to provide help with cracked render – we recommend sending pictures to us at firstname.lastname@example.org and we can provide expert opinion on the best solution to getting the issue fixed!