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
Seems to me that if all you did was hydro patch the ceiling cracks, all
you'll be doing there is make the leaking-in water find somewhere else
within the interior roof structure to move to and leak out of. Or worse,
maybe continually pool up and work on any cracks you don't/can't see
during freeze-thaw so the concrete starts coming down in big chunks
sooner or later.
Seems to me the best way to remedy it (short of trashing the patio) is
to not only redo all the mortar, but put a new seal on the roof itself.
Back in the day, they used to slop a thick coat of roofing tar with big
mops on flat roofs, but that was back in the day. Myself, I wouldn't own
anything with a flat roof on it larger than a tool shed even if someone
gave it to me for free, so I have no idea about the best way to seal a
flat building roof these days. A competent commercial roofing company
might be a nifty place to start for advice or an estimate.
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