I have a flagstone patio on the flat roof of my garage. Recently, during rains and snow melting, water seeps through the flagstone surface (probably through cracking mortar) infiltrating down and coming through cracks in the concrete ceiling of the garage, by which time it has picked up enough mineral content that it forms stalactites of minerals on the garage ceiling. The bad part is that it drips on the car and causes stubborn mineral stains on the car's finish. How would you go about waterproofing this? I have applied a concrete/patio sealer, but it didn't help. Dig out and replace the mortar around the flagstones? Maybe hydraulic patching cenment on the garage ceiling cracks and a super-duper masonry sealer/waterproofer on the patio surface? What's the best masonry sealer out there? All suggestions welcome.
-Howard