Window Waterproofing

Nearly a year ago now, I took up an issue with the builder about the stone mullion window surrounds letting in water. It was described in this post, and then again in this one. Here is a reminder of the problem :


At the time, the builder promised to get in touch with the manufacturers and arrange a site meeting. This didn't happen. The last contact I had about this was in April when I received a text from him saying he "hadn't forgotten and would sort something out after Easter".

Having heard nothing more, I recently got in touch with the manufacturer myself. I sent copies of all these pictures for their consideration. It seems they are baffled as to what the root cause could be. The damp patches do not appear consistently across the mullion, neither are they associated with the joints between the different components. They have recommended that I selectively treat part of one of the mullions with a breathable water seal compound (liquid goretex I suppose !) and monitor it to see if has any effect. They have recommended a specific product which they have had on trial and may start marketing under their own name, and today I have ordered 5 litres of it. It should be delivered Friday.