Sealers

["Peter Hill" <peterhill-rh@xxxxxxxxxxxxx>]

Hi Stoners,

Tim wrote "Why not try clay or lime (any form of calcium
carbonate)? Both are natural and with a little time
should fill up the pores in the stone naturally."

Seductive idea, but wrought with risks methinks.  Clay
has the property of expanding and shrinking,
dramatically, with water content.  Dry clay cracks and
shrinks, wet clay expands.  I have seen enough cracks in
garden lawns and huge cracks in the walls of buildings
because of clay soils drying out in summer.  Lime has
its shortcomoings too.

Lime and calcium carbonate are not the same thing.  I
would not recommend using any lime, cement like or
related product to seal a rock unless you had tried it
out for at least six months, preferable a year so that
you see it through a full set of seasons.  Mostly
because you will not be able to predict the reaction
between the lime based filling and the silicate or
carbonate minerals of the host stone.

I am struck by one correspondent's advice about sealing
stone that sits outside on the ground.  The only way to
truly seal it effectively is to seal it 100%, ie.
completely.  Big job.  As the correspondent said, the
stone draws moisture from the ground, and that must be
free to evaporate or escape in some way otherwise
internal physical and chemical reactions will, over
time, rot the rock internally.

Stone lasts longer than most of us, but it does age, and
it ages faster in certain weather conditions.  Part of
the beauty of older stone in outdoor setting is the way
that lichens and stains develop.  I guess that the
balance between that and a desire for preserving a
pristine surface depends of personal preference, the
nature of the rock and the local climate (I include such
local climate as under trees that may shed all sorts of
sticky stuff).   It is easier to accelerate weathering
with treatments than it is to retard it.

One thing's for sure, nature lasts longer than we do and
we have a tough job reversing its work.

Bottom line. For me, minimalist intervention in
maintaining the stone will serve better than any rough
tough, or chemical treatment.

A brief intro as this is my first foray into the list
after joining a couple of weeks ago. Once a
mineralogist, petrologist, geologist I moved into the
oil business on the IT then the management side.  Now
semi retired, late 50s,  I have taken up drawing and
painting recently on route to sculpting in stone.  Like
many in the list, I have a strong connection,
attraction, to stone ( I would say rock, but the
sculptures vocabulary speaks and writes of stone), its
look, its feel, texture, .....   earlier this year I
walked into a small gallery in Cockermouth (Lake
District, UK) and saw a piece I had to touch, rest my
hand on.  The young woman who made it was working out
back and we talked.  That released something that has
been in me.  When I have mastered my hand eye
coordination with a pencil and paper and with a paint
brush ( I am practising and going to classes with a
great teacher, Robin Palmer) I will move on to 3D and
stone.

I live near Aberdeen, Scotland and I wonder if anyone
knows of a supplier of materials in this part of the
world?

Best wishes stone knappers, everywhere.

Peter

Peter Hill