>We have an 1831 building on top of a headland adjacent to the harbour.
The building is constructed of limestone blocks quarried from the headland.
 Most, but not all, of the blocks were caprock, the hard calcrete which
occurs just below the surface of recent limestone deposits.  This also
occurs across the top of the headland.

Advice from a retired mining engineer (my father):

    Thanks for the info from Australia. they sure have a problem. How can you
beat mother nature?

    The reason the limestone below the caprock is soft, besides it original
formation, is that water gets to it through the cracks in the cap rock. If
you want to slow down the weathering process, put a big apron over the cap
rock. This could be installed under the soil like your house aprons. How wide
would it have to be to form a barrier, 10 or more feet? That would be
dependent on the thickness of the soft limestone. The thicker the formation,
the wider the apron would have to be. The length is dependent on the area you
want protected.

    Since the area is adjacent to a harbour, you have weather coming in from
the ocean all the time effecting the exposed limestone. The exposed face
could be covered with shotcrete.

    Further research can be done by contacting the Highway Departments of
mountainous states. They run into similar problems all the time with
different geologic formations. Exposed coal in cuts  in Pennsylkvania has
always been a problem to them but in this case the heigth of the seam may not
be anywhere close to the height of the exposed soft seam in Australia.

    Tennesse has similar problems with higher cuts. They protect the faces by
drilling holes into the formations so the water may drain out and not stay in
to do damage. The holes are drilled at the bottom of the cut and at an upward
angle of up to thirty degrees. Maybe, in Australia, if the have a tunnel
below the formation they could go in and drill a ring of holes upward. The
number of rings would be dependent on the area to be protected.

    The main thing is to get rid of the water to slow down the decomposition.
Just like you told me to drill holes at the bottom of my columns. They could
start anyplace and expand the area to be protected as funds become available.

    Thanks for letting me put in my two cents worth.