What Materials Can You Render?
Do you have a tired-looking fibro or concrete (besser) block and wonder what you can do to freshen it up and make it look nice? Render is a possible answer. Believe it or not, you can render most common building and construction materials found in Australia.
However, each material requires a slightly different approach to achieve a high-quality, aesthetic finish.
Continue reading to learn more about the different materials you can render and the different methods you need to use for each one.
Rendering and Sydney Homes
Sydney’s homes are a versatile mix of older brick cottages, terrace houses, apartment buildings, Art Deco homes, Federation homes, Queenslander homes, and contemporary homes, meaning there is no one-size-fits-all approach to rendering.
Each architectural style and suburb in Sydney comes with their own set of challenges. Beach suburbs and coastal areas have to deal with salty ocean air eating into old building joints, while homes in Western Sydney are exposed to strong sun rays which can cause paint and render to fade faster. Inner-west terraces have soft, crumbly brick that needs to be prepped properly before any render goes on.
Render has both aesthetic and protective properties, offering many benefits, including increasing a home’s kerb appeal, transforming it from ‘blah’ to ‘wow’, and protecting it from the elements and water damage. But all these benefits only work if the correct methods are used properly.
Materials You Can Render
Porous Materials
Porous materials and surfaces contain minuscule holes or spaces that allow liquids or particles to pass through them. These tiny pores act like an absorbent sponge, which enables other materials, including renders, to securely bond with the substrate, resulting in higher-quality and longer-lasting rendering jobs.
Most porous materials can be rendered over, provided they are well prepared to prevent cracking and moisture from entering the walls.
Brick
A brick is a small rectangular block made from baked clay and sometimes other materials. It is one of the most popular construction materials in the world and is commonly used to build homes.
Brick is the most common material rendered in Sydney, as it generally performs very well (both aesthetically and functionally) and is long-lasting. Brick is a naturally rough and porous material that gives render something to bond to, which is one of the key reasons why brick and render go so well together.
There is one downside, though: Older brick structures, especially in heritage areas found in the Inner West and the Eastern suburbs, may have softer bricks that flake (spall) on the surface.
If you apply render over a soft or flaking brick wall, it will crack and fall away from the brick within a few years, meaning you will have to spend time and money repairing it.
So, what’s the solution? We recommend either applying a bonding agent over the brick or removing the loose material and repointing it (removing the old mortar and replacing it with fresh mortar).
Concrete Block (Besser Block)
Besser blocks (also commonly called concrete blocks) are rectangular concrete blocks widely used on construction sites across Australia. They are strong, versatile and fire-resistant, making them highly favoured in the construction industry.
You will find besser blocks all over Sydney, from garages to older extensions and retaining walls. Their dense, porous material ensures the render bonds properly to the wall, especially when the joints are filled.
The most significant risk when rendering besser blocks is that moisture may be trapped behind the walls without you realising it. If the moisture isn’t removed or drained before the render is applied, the render may eventually come away from the surface or blister, making it look unsightly.
Concrete
Concrete is the most widely used and manufactured construction material in the world due to its durability, strength, relatively low cost, and ability to withstand fire and the elements. It consists of cement, water, aggregates (sand and gravel) and additives which change its functional properties.
Most concrete surfaces can be rendered; however, their smooth surface makes them less porous than other materials such as brick or besser blocks. To resolve this, a bonding agent, a scratch (key) coat, or a polymer-modified render should be applied to the concrete surface before the render is applied to improve adhesion.
Fibre Cement Sheeting
Fibre cement sheeting is a building board made from a combination of cement, sand, cellulose fibres (natural or semi-synthetic polymers), and water. They are durable, moisture- and fire-resistant, and provide a low-maintenance alternative to brick or timber. Fibre cement sheeting can be found on eaves and cladding on exterior surfaces. It was also commonly used on many project homes from the 1990s onwards.
Fibre cement sheeting can be rendered, but it requires a flexible render, such as acrylic, to prevent cracking along sheet joints, as the fibre cement moves differently to other masonry substrates.
If you want to render fibre cement sheeting, make sure you select an acrylic or polymer-based render for the best results.
Lightweight EIFS (Exterior Insulation and Finish System) and Foam Panel Systems
Lightweight EIFS are synthetic exterior wall claddings that combine insulation with a water-resistant rendered finish. It provides an aesthetic finish that has thermal efficiency.
Foam Panel Systems consist of a thick, insulating foam sandwiched between two structural and protective facings. They are used on walls, roofs and floors.
These materials can be rendered, but they need a thin-coat acrylic render as cement render will only crack over such a lightweight material.
AAC Panels (Autoclaved Aerated Concrete)
AAC Panels are lightweight, steel-reinforced building materials made from cement, lime, sand, and water. They are much lighter than concrete and provide insulation, soundproofing and fire resistance, making them popular in contemporary Sydney homes and buildings.
Because AAC Panels are porous and lightweight, render can be applied to them, but, as with other substrates, they need to be prepared beforehand with an appropriate sealer or primer to prevent moisture from entering the walls.
Old Existing Render
Can you render over an existing render? Yes, for sure. However, the old render needs to be in relatively good condition (not cracked, lifting at the edges or falling away from the substrate (drumming).
If you cover up a render that is in poor condition, it only hides the problem; it doesn’t resolve or eliminate it. The damage will eventually reappear and be even worse than it was before, resulting in higher repair costs.
Materials You Can Render: A Comparison
| Material | Suitability for Rendering | Preparation Required | Typical Lifespan of the Render |
| Brick | Excellent | Remove loose mortar and replace it with new mortar. Apply a bonding agent | 15-25 years |
| Besser (Concrete) Block | Excellent | Fill the joints and check for moisture in the walls (make sure the drainage works) | 15-25 years |
| Concrete | Good | A bonding agent or scratch coat is required before the render is applied | 15-20 years |
| Fibre Cement | Good | It works best with a flexible render type like acrylic render | 10-15 years |
| AAC Panels | Good | It requires a primer and sealer | 15-20 years |
| Lightweight EIFS | Fair | It only works well with an acrylic thin-coat render system | 10-15 years |
| Old/Already Existing Render | Fair | It needs to be in good condition and needs to go through sound testing and be repaired if required | It depends on the condition of the old render and the quality of the new render that is applied |
Common Mistakes Made with Render Materials
Some of the most common mistakes we see with render materials include:
- Skipping a bonding agent: If you fail to apply a bonding agent to a smooth substrate like concrete, the render will not bond to the surface.
- Rendering over old render: If you render over old render without repairing or removing it first, it will only temporarily cover up any problems; it will not completely remove them. And before too long, the issues will be visible and even worse than they once were.
- Ignoring drainage behind retaining walls: You fail to check for moisture behind besser (concrete) blocks and properly drain it, leading to bubbling render, pressure, and moisture damage down the line.
- Using cement render on fibre cement or EIFS (Exterior Insulation and Finish System) panels: The heaviness of the cement render will not hold up well on the lightweight materials of fibre cement or EIFS panels. You will need to use a more flexible render type, such as acrylic, which is better suited to lighter materials.
- Rushing the rendering and curing process: If you rush the rendering and curing process, especially in warmer weather, it can cause cracks to form across the render.
- Rendering over damp or salt-affected brick: If you fail to address the moisture content before applying the render, it will cause the render to fail, blister or fall away from the substrate.
What Materials AREN’T Suitable for Rendering
Professional rendering companies do not recommend that you render over the following materials:
- Glass
- Aluminium Composite Panels (ACP)
- Metal cladding
- Wood-plastic Composite (WPC) Panels
- Acoustic Composite Panels
- Timber weatherboard
- Steel
- Silicone or wax-coated surfaces
- Glazed tiles
- Untreated plywood and timber
Contrary to popular belief, timber and wood CAN be rendered, but not in the traditional way. It is a much more complex and time-consuming process: you will need to use a carrier board or a timber-frame render, along with a breather membrane to allow ventilation.
The render cannot be applied directly to the timber, as it is not waterproof and will warp and bend.
At Sydney Cement Rendering, we take pride in being Sydney’s trusted rendering experts. From residential jobs to large-scale commercial projects, we provide our customers with the highest-quality rendering services and adapt to every situation and rendering style. To learn more about what materials are best for rendering and to get an accurate quote, give us a call at 0402 704 984 or visit our website https://sydneycementrendering.com/ to find out more about the services we offer!
FAQs
Can I Render Over Old Paint?
We don’t recommend it because the render won’t bond to old paint properly. It is better to apply the render directly to a bare substrate.
How Do I Know if the Brick is Too Soft to Render Over?
To find out for sure, conduct a simple scratch test by scratching the brick with a screwdriver or key. If it flakes or crumbles, it will need to be repaired before the render is applied.
Sydney Cement Rendering can also conduct a thorough moisture and condition assessment.
Do I Need Council Approval Before Rendering My Home?
In most cases, no, as rendering does not change the home’s structure or layout. However, you may need council approval if you are rendering a heritage-listed home or homes in a conservation area.
Can Rendering Fix Damp Walls?
No, although rendering can add water-resistant properties to a structure, it doesn’t fix an already existing or underlying moisture problem.
Any moisture issues need to be addressed before render is applied to the substrate.
How Long Does Render Take to Dry and Cure?
It can take a full day or two for the render to dry, but it can take several weeks for it to reach full strength (cure).
This depends on various factors, such as the weather, the render type, and the render thickness.
Can You Render Over Old Render?
Yes, but the already existing render needs to be of good quality. If it is cracked, lifting away from the wall or sounds hollow when it is tapped, it means it is damaged beyond repair and should be removed before a new render is applied for the best results.