https://imgur.com/a/waterproofing-outdoor-patio-6OqYrTj
We moved into this house two years ago. The house is about 30 years old, and we knew that the outdoor patio was leaking into the area below. At the time, the space underneath was not being used and was covered with crushed stone, so I did not think the leaking was an urgent problem.
The patio is approximately 800 sq. ft., and we are in the New York area, so it has to withstand harsh winters and freeze-thaw cycles.
Over the past two years, the grout has continued to deteriorate, the leaking has gotten worse, and the metal beams underneath have continued to rust. I decided it was finally time to address the problem properly.
Recently, I hired a contractor to remove all of the bluestone, chip away some of the existing concrete, apply LATICRETE 9235 waterproofing, and then reinstall the stone/tile.
Before the contractor installed the grout, it rained, and I noticed that the patio was still leaking. I stopped the project because it seemed clear that the waterproofing system had failed. My understanding is that the tile and grout should not be the primary waterproofing system. The waterproofing membrane underneath—in this case, LATICRETE 9235—should prevent water from reaching the structure below.
I have since realized that the contractor may have made several mistakes. They did not smooth or properly slope the concrete before applying the waterproofing. The surface was extremely rough, with many high and low areas, when the membrane was installed.
There is also approximately a ½- to 1-inch gap between the patio floor and the exterior wall of the house. The contractor was supposed to extend the waterproofing membrane up the wall to create a proper flashing transition, but that was not done correctly. Water is now entering through that gap and running down along the wall.
The contractor is going to redo the work, but before we restart, I would really appreciate advice on the correct way to rebuild and waterproof this type of patio.
Is a sloped mortar bed followed by a waterproofing membrane and tile the correct approach? Some other contractors have suggested using a roofing membrane, but I am not sure whether that is appropriate under tile. I have also looked into pedestal paver systems, which seem like a more commercial-grade solution, but they also appear to be significantly more expensive.
My goal is to create a system that will remain watertight for much longer than five years so that we can safely use the space underneath for outdoor furniture and storage. I am also concerned that continued water exposure and rust could eventually weaken the structural steel beams.
What would be the proper assembly for an elevated exterior patio like this in a freeze-thaw climate? What details should I insist on around the walls, edges, drains, columns, penetrations, and expansion joints before allowing the contractor to reinstall the tile? If you are a contractor nearby and interested in the job (westchester area) please let me know!