How to maintain a fibre cement slate roof?
Like any roofing material, a slate roof is subject to pollution and ageing. Over time, dust and atmospheric pollution are deposited on all roof coverings. Moss is also difficult to avoid and is not peculiar to the type of roofing material, as it can adhere to all types of materials.
In fact, it is not the slates that turn green. It is the dust and dirt that ends up on the slates, which is an excellent growing ground for mosses and algae.
Natural grey slates are not treated. Their surface is therefore more susceptible to pollution. The coated slates are optimally protected against pollution thanks to their low porosity and the moss repellent in the coating, but external factors still play a major role in whether or not the roof turns green.
Cause of contamination
The intensity of moss formation is highly dependent on:
- the orientation of the roof surface: mosses develop mainly on the parts of the roof that have little or no exposure to the sun, such as on roof shingles facing north or that are perpetually in the shade ventilation between the under-roof and slates: good ventilation reduces the length of time the roof covering remains damp.
- Mosses and algae form on sand and dust particles, which adhere most easily to a wet surface. Good ventilation between the under-roof and the slates therefore contributes significantly to the rapid drying out of the roof covering and thus also slows down moss formation the presence of green areas in the immediate vicinity: the proximity of trees or greenery obviously also has an adverse effect
- "Acid rain" forms on the roof the acidic environment in which mosses and algae thrive excellently
Going green does not affect the quality of the slates. But for the sake of appearance, longevity and waterproofing of the roof, standards and regulations provide for regular maintenance.
Annual interventions:
- Moss removal and, in general, removal of overgrowth and all kinds of debris that could impede the proper functioning of the roof covering
- Maintenance of the rainwater drains
- Checking fastenings, mainly at the eaves
- Replacing and replacing missing, broken or shifted elements
- Plugging of damaged grooves at the level of the lead seals and waterproofing of the parts of the structure not protected by the rainwater seals
To carry out maintenance, a firm specialising in roof cleaning can be consulted. If you want to do it yourself, there are specific products on the market to clean the roof.
Working method
Mechanical cleaning
Moss is removed by brushing the roof with a firm brush. Do not use a metal or overly rough brush. Avoid scratching the surface of the materials, as dust particles settle faster on a rough surface, which only encourages moss growth. Finally, rinse the roof thoroughly. In doing so, avoid dust and moss getting into the cistern.
Chemical cleaning
When the roof is completely dry, a good moss control product is applied that penetrates sufficiently deep into the material to kill all moss and algae germs.
Depending on the product used, after sufficient penetration, it may be necessary to remove the dead mosses from the roof by brushing or rinsing. Rain drains should be disconnected during the works to avoid these residues and the applied product entering the cistern.
Products affecting the slates, coating or metal parts of the roofing (nails, storm staples, hooks, gutters, etc.) must obviously not be applied.
The safety aspect during roofing and maintenance work has not been addressed in these technical data. Please refer to the nationally applicable safety regulations.