We keep hearing about mould infestation in roof plywood and rainscreen panels. Can't something be done to prevent it?
Yes, as the picture shows, plywood has been installed as a wind barrier in this building. The difference is that one of the sheets in the picture was treated with ProtoxAquagrundand the other was untreated - guess which one?
Moisture and temperature variations in roof plywood cause mould
Even if the ventilation in the roof space has been carried out according to all regulations, there is an imminent risk of mould growing on the roof plywood in such a structure. This is due to the natural moisture and temperature variations in the structure.
When the sun shines on such a roof surface, it can reach 60 degrees centigrade. This means that the air inside the roof space is also very hot and can therefore contain a lot of moisture. When the sun goes down, the temperature of the roof veneer drops rapidly and the cold surface causes condensation.
The moisture that condenses on the plywood can only "be" in the outermost 1.5 mm thin veneer layer, because just below it there is a completely waterproof glue joint that the moisture cannot penetrate. This means that the top veneer layer will very quickly become wetted to above the critical 15 % wood moisture, and then mould growth will occur.
How to prevent mould in roof plywood
The right way to prevent this is to treat the underside of the roof plywood with ProtoxAquagrund, before installation. ProtoxAkvagrund is an approved wood preservative that prevents both mould and wood-degrading fungi. With a MAL code of 00-1, it can be applied with a simple garden sprayer and once and for all solve the problem before it occurs.
Once mould growth has started as shown in the picture, cleaning with ProtoxHysan An option, of course, but prevention is many times easier, not to mention cheaper, than cure.
Learn more about growing conditions, treatment and prevention of mould here.