The Role of Render in Moisture Management
When it comes to rendering buildings in wet climates, selecting the right material is essential for protecting walls from rain, sea spray, and mould. In today’s world of cement and silicone renders, it may seem straightforward that rendering serves primarily to keep the elements out. However, few realise that it also plays a crucial role in allowing old masonry to release excess moisture through its breathable surface, which is vital for managing the building’s moisture levels. Insufficient breathability is a significant drawback of modern renders.
Historically, the relationship between breathability and water resistance in rendering materials was quite different. Lime renders were known for their high breathability but were not waterproof. During periods of heavy rain, traditional lime renders would absorb significant amounts of moisture, which could then transfer to the underlying masonry, resulting in damp patches on the interior surfaces.
As you can see, achieving a lime render that is both breathable and waterproof is an admirable goal, yet one that has been challenging to fulfil throughout history.
Breathable & Waterproof Ancient Technology for Modern Problems
Ancient Roman architects were among the first to use waterproof yet breathable lime renders, particularly in baths, aqueducts, and harbours, where structures were in constant contact with water. By adding pozzolans (volcanic soils) and cocciopesto (milled terracotta) to lime, they developed a render that was durable, water-resistant, and breathable—a technology that was largely lost after the fall of the Roman Empire.
Below, we discuss a lime rendering system that reinstates these time-tested Roman methods, delivering 21st-century comfort for property owners while preserving the breathable nature of the building fabric.
EFFICIENT LIME RENDERING SYSTEM
for Old & Listed Buildings
The system is highly breathable, does not trap water inside the building fabric, thus minimising the danger of any frost damage. It also prevents the formation of mould which occurs in presence of stagnant moisture.
Step 1: Structural Repair with Betoncino Consolidante MGN
The rendering process starts with masonry repair. Older buildings often have uneven or damaged bricks, and sometimes sections have eroded entirely. Betoncino Consolidante MGN, a structural-grade lime mortar, is perfect for filling even large gaps. As opposed to what its name suggests this is a lime mortar for structural consolidation and repairs, which not only smooths the wall but also bears the weight of the surrounding masonry.
Step 2: Waterproof Base Coat with Rinzaffo MGN
To put this into perspective: as mentioned above, ordinary lime renders are typically not waterproof, meaning they can become saturated, allowing moisture to reach the masonry behind. This pozzolanic base coat, however, prevents rainwater from soaking into the masonry while still allowing interior moisture to evaporate. For further details on how this works, please see the product page.
Step 3: Decorative and Breathable Top Coat with Sanacolor 2000 MGN
Sanacolor 2000 MGN is a traditional, mildly water-repellent lime render. Coloured throughout, it eliminates the need for periodic repainting, providing a maintenance-free finish.
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Breathable
Being a lime plaster, it is naturally vapour permeable or breathable
Waterproof
Once set, it copes with weather and rain very well
100% Natural
No cement or chemicals, natural materials, only
Application Tips
0. Preparation of the Wall Fabric
Remove old render and any loose or foreign materials (like wood, tar, or metals). Clean the surface thoroughly to eliminate all debris and residues, then wet the surface before applying the render.
1. Masonry Repair
Where necessary, repair the masonry with Betoncino Consolidante MGN to maintain structural integrity.
2. Applying the Rinzaffo MGN Base Coat
- Mix the package contents with clean water until a smooth, creamy paste forms—avoid overworking.
- Apply a 10 mm coat, covering the entire surface. For areas with excessive dampness, apply a second coat with fibreglass mesh between the coats. Allow a 24-hour drying time between coats.
3. Applying the Main Coat
After the Rinzaffo MGN base coat is dry:
- Mix Sanacolor 2000 MGN with water for a uniform consistency, limiting mixing to 5 minutes.
- Apply a 10 mm coat, and once dry, follow with a 4-5 mm finish.
For different finishes:
- Use a stainless-steel trowel for smoothness, or a sponge float for texture.
Allow 3-10 days for the surface to dry, keeping it protected from rain and excess moisture.
In Conclusion
Wind-driven rain is a significant issue, particularly in coastal areas, as it can saturate the building fabric. This saturation leads to staining, damage to internal decorations, and long-term structural issues. Salts dislodged by the driving rain can dissolve in water and migrate to internal surfaces, resulting in efflorescence and crumbling of the wall fabric.
With this rendering system, we aim to reverse the ongoing decline of your old home, investment property, or project. We are pleased to offer a long-lasting solution, confident that this system will enhance the value and appearance of your building.
