In summary
The clouding effect observed with RC KALEI is a temporary colour variation that occurs when rainwater is absorbed into the open pore structure of the breathable limewash mortar. This is not damage, but a natural and technically positive phenomenon that shows the façade can breathe and regulate moisture effectively. If a more uniform appearance is desired during rainfall, the façade can be treated with a breathable water repellent such as RC HYDROCREME 4 or a breathable paint system such as RC SILOXCOAT, without compromising the vapour permeability of the system.
When a façade is finished with RC KALEI, subtle colour variations can often be observed during rainy weather: certain areas temporarily become darker than others. This phenomenon is commonly referred to as the clouding effect. With a breathable, cement-free limewash mortar such as RC KALEI, this is not a defect or damage, but a natural and technically explainable behaviour.
Capillary action and pore structure
A cement-free limewash mortar based on natural hydraulic lime has an open pore structure. This open structure allows water vapour to migrate and enables the wall to breathe. When rainwater reaches the surface, it is temporarily absorbed into the fine capillary pores of the limewash layer. As a result, temporary darker cloud-like patterns appear. Once the façade dries, these differences disappear completely. This phenomenon is typical of lime-based, breathable systems and does not occur with fully sealed cement-based or synthetic resin façade coatings.
The clouding effect on older solid walls
From a building physics perspective, the clouding effect is an indication that the limewash layer is functioning correctly. It shows that the limewash mortar, RC KALEI, is breathable and that the façade is capable of temporarily absorbing and releasing moisture. This is particularly important for older solid walls without a cavity. A breathable system helps prevent moisture accumulation within the structure, reduces the risk of salt damage and limits frost stress during winter. A limewashed façade that remains completely uniform and unchanged during rainfall often indicates a more closed finishing system or the presence of an additional water-repellent treatment.
Reducing or preventing the clouding effect
Although the clouding effect is technically a positive characteristic of a breathable limewash mortar, it may sometimes be perceived as aesthetically undesirable, particularly in modern, minimalist architecture, on large uniform façades, with light colour tones or on façades exposed to prolonged driving rain. To reduce or prevent the clouding effect, the façade can be treated with a breathable paint system such as RC SILOXCOAT or a breathable water repellent such as RC HYDROCREME 4.
RC HYDROCREME 4 is a high-quality, concentrated breathable water repellent in cream form. It reduces water absorption without affecting vapour permeability, making the surface water-repellent and significantly limiting temporary colour changes during rainfall.
RC SILOXCOAT is a high-quality, water-based siloxane façade paint with an ultra-matt mineral appearance. It combines very high vapour permeability with strong water-repellent properties, ensuring façades remain protected against rain and pollution while maintaining their breathability. Thanks to its self-cleaning effect and excellent durability, it is an ideal finishing system for limewashed façades.
Every façade is different. The absorption of the substrate, the orientation of the building, the chosen colour and the desired appearance all play a role in the final result. Are you unsure whether the clouding effect is desirable for your project? Or would you like to know whether a water repellent such as RC HYDROCREME 4 or a paint system such as RC SILOXCOAT is recommended?
Contact our representatives for specific technical advice tailored to your project or site, ensuring a durable and aesthetically correct result.
.avif)
