I have a 70 year old house with a deck off of the second floor master bed room. Below the deck was a porch that I closed in 20 years ago. Almost from the beginning, I have had a couple of small leaks in corners (although the location really means little considering how water tends to run). The owner of the premier multi-state waterproofing company is a friend and he has a crew fool with it 10-15 years ago. It has started to leak again. I intend to call my friend and offer to pay to have this checked again. There is slate on the deck. The problem is primarily due to standing water and lack of slope to the drains. Has there been any progress in products that can be applied to slate or tile to waterproof in the last 15 years? Any ideas? I’d like to get a working knowledge of various products so I can have an intelligent conversation with my friend. Thanks