As you know, bay windows are notorious for leaks. A client had one which was leaking heavily. He stripped off the current substrate and re plyed the areas where the substrate was rotting. He left some butynol on there and liquid rubber was used to adhere that to the new substrate (Waterproof sealant is also an adhesive which is why it bonds so well to its substrate). He then used the geofabric in unison with the waterproof sealant over the joins and screw holes before applying a coat over the whole area making it water tight. This saved the client hundreds of dollars and meant the whole thing could be done in one day.