Right lads i can clear this up. My uncle tried this on his new bmw which has had a sealant applied when he bought it although its never seen any wax. i witnessed it first hand and to be fair the results were outstanding, the water just sheeted off and sort of evaporated away. Whilst my car was at his i decided to give mine a go, which is layered with collinite 915. My results were terrible, no sheeting, pools of water left on the flat surfaces, water spotting etc etc.
With this in mind i decided to contact tetrosyl who make this to explain my results. This is there reply quote,
"I have been speaking further to our Technical staff and they have advised that with regards to the different effect on various panels, we guess that the horizontal panels differ to the vertical panels (ie roof/bonnet/boot lid Vs doors/wings/quarter panels)? The may be simply due to the orientation of the surface.
Liquid Gold does not contain wax but it does contain another ingredient which leaves a microscopic coating over the external surfaces which provide the self drying 'wetting' properties which is different to the protection offered from a wax. The product will not strip wax from the surface any more than a conventional car shampoo".
They did tell me that you would not get the full "wetting" properties if your car is waxed. My conclusion is that if you wax your car then this is a waste of time/money. Hope this clarifies a bit.