Professor Erhard Winkler is a great guy.

He has several theories relating to the bending
marble, but is also quite insistent that exposure to
moisture substantially reduces the strength of marble.

And has some research data to prove it.

My attitude to bending marble is that it can be caused
by a number of things, but is primarily related to the
a particular characteristic of calcite crystals (of
which pure crystalline marble is composed) to expand
in two directions and contract in the third when
heated (and vice versa when cooled).  As a result,
there is a hysteresis effect (read it doesn't go back
to where it originally came from) over time, and the
marble gets bigger.  If there are different things
happening on each side of a panel of marble, then the
panel can bend.  This is why sometimes the marble will
bend one way, and sometimes it will bend the other.

At Finlandia Hall in Helsinki, designed by the great
Alvar Aalto, the Carrara White marble cladding all
bowed.  After 20 years, the panels were all cupped up
to 50mm (2") over a 1800mm (6') length.  That is, the
centre had gone back into the building, and the ends
had come out.

The cladding was pulled off and replaced with new
Carrara marble in 1998-1999.  This has already started
to bow again ... but this time it is pillowing
outwards.  Something to do with a different fixing
system, in my opinion.

At the end of the day, the word is ... don't use thin
crystalline marble on the outside of buildings if you
want it to stay flat.

As a sidenote, I heard a story from one of the guides
at Finlandia Hall about a group of Japanese architects
who came to visit, and asked where they could get the
curved marble panels from.  I think this is an urban
myth, but you never know ...

Cheers
david

 --- Ken Follett <[log in to unmask]> wrote: > E. M.
Winkler author of Stone: Properties,
> Durability in Man's Environment,
> Springer-Verlag, 1973-75 about 6 years ago at an APT
> conference (Washington?)
> talked about his study of bent marble on mausoleum's
> in New Orlean's
> cemetaries. I do not remember what he said the cause
> was.
>
> ][<en
>
> --
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