> I would expect things weritten on vertical surfaces to be less
> affected since
> gravity will tend to pull the water down through the stone
> rather than out the
Not necessarily. For example, if limestone sits directly on the ground (or anything containing moisture), the strong capillarity of limestone -- due to its porosity -- sucks up moisture against gravity such that salt and mineral crystals form on the TOP of the stone. However, lifting the stone off the ground (by perching it on small, thin blocks) minimizes such mineralization.
Note that among the greatest salt deposits found on any blocks within G1 were those on the upper walls at the south (highest) end of the Grand Gallery, the antithesis of what we'd expect if gravity was responsible for such mineralization.