Rendering Over Stone Walls: Everything You Need to Know
Do you have an outdoor stone wall or an indoor stone feature wall that you want to transform? The good news is that you can render it. But rendering a stone wall is not the same as rendering a brick or concrete wall. Applying render to a stone wall requires a different approach, especially when rendering a sandstone wall.
Continue reading to learn more about everything you need to know about rendering stone walls.
Why Rendering Over Stone Walls Requires Different Treatment
Unlike brick and concrete block surfaces, not all stone walls are porous and different types of stone hold moisture differently, move when temperatures shift, and often sit on lime mortar rather than cement.
Stone walls need to breathe to allow moisture to escape, making them best suited to a lime render.
The Type of Stone Walls You Can Render
The stone walls best suited for rendering include:
- Sandstone and limestone: Both sandstone and limestone are highly porous and work best with lime renders, which allow them to breathe. If cement render is used on sandstone or limestone, the moisture will remain trapped, and the stone will become damaged.
- Granite, slate and basalt: These stones are dense and non-porous, which makes it more difficult for the render to bond with the stone. Although they can still be rendered, it will require special preparation such as wire lathing (a reinforced base) and a specialised bonding agent before the render can be applied.
Which Render Type is Best for Your Stone Wall?
Lime Render
Lime render is a highly breathable, traditional render type made from lime, water and sand. It acts like a second skin; its porous nature allows moisture to safely evaporate, preventing mould growth and structural damage. It is mostly used on historic and heritage-listed structures.
Cement Render
Cement render is one of the most popular render types due to its relatively low cost, durability, resistance to the elements, and aesthetic finish. It is made from cement, sand, water and lime.
If your stone wall is sandstone or limestone, an original retaining wall, a heritage terrace, or has been around since the pre-1930s, a lime render is strongly recommended.
On the other hand, if your stone wall is fairly modern and has a solid backing, cement render can be used.
Sydney Cement Rendering can determine which render is best for your stone wall, depending on the age and condition of the stone, the type of stone it is and what the wall is used for.
Cement Render vs Lime Render for Stone Walls
| Feature/Property | Cement Render | Lime Render |
| Breathability | Low. It traps moisture in walls, leading to structural damage | High breathability. It lets moisture escape naturally |
| Flexibility | Rigid and more prone to cracking when applied on walls that shift naturally over time (older buildings) | Flexible and shifts with the building’s natural movement, reducing risk of cracks forming |
| Drying and Curing Time | Fast drying and curing times, but moisture may be trapped under the surface if it is not dried and cured properly | A slower drying and curing time, but it often results in a higher quality finish |
| Costs | Lower labour and material costs | Higher costs due to specialised labour |
| Repairability | Can be patch-repaired, but doesn’t look too flattering | It has the ability to self-heal small cracks over time |
| Suitability | Newer stone walls or stone walls that have a cement-based backing | Older sandstone and limestone walls, and heritage-listed and historic structures |
The Process of Rendering a Stone Wall
To render a stone wall, either with cement or lime render, follow these steps for the best result:
Inspection
Check the stone and the area behind the wall: is there any water damage, cracks, or unsightly patch-ups?
Preparation
Remove any loose debris or materials, old paint and repair patches. Rendering will work best when the stone is clean and free of any debris.
Repair
Any mortar joints that are falling apart need to be repointed by removing the damaged mortar and replacing it with new mortar.
Apply a Key Coat
For an uneven stone surface, it is important to apply a key coat that consists of a bonding or scratch coat (often with the extra reinforcement of mesh), so that the render bonds well and is supported on the uneven surfaces.
A Base Coat is Applied
Apply the first layer (base coat) of render to the stone wall and let it dry completely before applying the next layer.
Most rendering problems occur because not enough time is allocated for the base coat to dry properly.
Finish Coat
The final render layer is applied. A textured or coloured finish is added at this point.
Curing Process
The stone wall needs to be kept damp and protected as the render fully dries and cures, which takes days for cement render and weeks for lime render.
Although rendering a stone wall can be a DIY job, for the best, long-lasting results, we recommend that a professional rendering company, like Sydney Cement Rendering, complete the job.
Common Mistakes When Rendering a Stone Wall
Here are some of the most common mistakes we see when people render a stone wall themselves:
Rushing the Curing Time
If the curing time of a rendered surface is rushed on hot days, it can cause the render to dry too quickly, making it much more prone to cracking over time.
Ignoring the Problems Behind the Wall
If you notice damp spots or a blocked weep hole (engineered gaps in external structures that allow trapped moisture to escape and provide much-needed ventilation), it will cause problems down the line, no matter how good the render job is.
Skipping the Key Or Scratch Coat
Stone is a naturally uneven material, and if you apply the render without first applying a key or scratch coat, it is prone to cracking and falling away from the stone.
A key or scratch coat will allow the render to grip to the stone surface securely.
Using a Waterproofer On the Stone Wall
If you apply a waterproofer to the stone wall before the render, it can trap moisture behind the render and damage it, resulting in a lower-quality rendering job.
Using the Wrong Render
If you use a cement render on a lime-mortared sandstone, it won’t last long and will eventually crack, allowing moisture in.
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 rendering over stone walls 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
How Long Does Render Take to Dry On a Stone Wall?
Cement render has a shorter drying and curing time (a few days for drying and about a week for curing), while lime render takes longer to cure properly (usually up to a few weeks).
Can You Render Over Any Stone Wall?
Most stone walls can be rendered, but you have to take into account the stone’s age and condition, as well as the mortar originally used.
Older sandstone or limestone walls with lime mortar will naturally require a lime-based render rather than a cement-based one.
Is Cement Render Safe for Limestone or Sandstone?
If the stone wall is in good condition and shows no signs of moisture damage, cement renders can be used.
However, if the sandstone or limestone is older and has signs of damp, we recommend using a lime render, as cement render traps moisture and can cause many issues down the line.
Do I Need to Remove Old Mortar Before Rendering?
Any loose or crumbling mortar needs to be removed and replaced with fresh mortar (repointing) before any render is applied. Rendering over unstable mortar only hides the problem, but does not remove it completely.
Can I Paint Over a Rendered Stone Wall?
Yes, once the render has fully dried and cured, you will be able to paint over it.
If you paint over it before the curing process is complete, moisture can become trapped, and the paint will only bubble and peel.
Will Rendering Damage a Heritage Sandstone Wall?
No, as long as you use the right render. For heritage sandstone, we strongly recommend a lime-based render that will allow the sandstone to breathe.