At significant expense (£34k just for materials) I have installed a product called Thermoash otherwise known as Hotwood; it's ash that has been treated under pressure to give it Class 1 durability. The product is sold as being virtually indestructible (maintenance free, resistant to rot, cracking, warping, etc). It's basically a form of real wood rainscreen. It sits on plastic clips fixed to battens 25mm from the building wall surface (the building is wrapped in a special version of Tyvek) and it is supposed to add to the thermal efficiency, etc, of the building. After a year since installation I'm seeing mould appear on it and also a difference between the battens. The manufacturer (Carpentier from Belgium) blamed me saying the installation was incorrect but that's simply not the case and after I showed them the installation was good they since refused to accept any responsibility. Then they told me to clean it regularly; what happened to 'maintenance free' ? I'm now left with a horrible looking rain screen. Does anyone have any experience with this problem and how to fix it?