Eric

In belated response to your question

... firstly thank you for the honorific - I struggle
with it, because I always think that Mr West was my
father, the schoolteacher ...

But on with the real issue.

Artificial sandstone using epoxies as the binding
agent had a flurry of popularity over a period of
about 15 years from the mid-1980s through to around
2000, here in Australia (and in Sydney in particular).
This is not to say that it is not used any more, just
that it is not so popular amongst specifiers.

Many of the repairs during the period 1985-1991
performed reasonably well.  One of the common features
was that the mix was the subject of careful
experimentation by a single person, Corrado (Con)
Tassi.  His work is perhaps best represented by a
series of bracketed pinnacles on the spires of St
Andrew's Cathedral in central Sydney.  I must check
these out some time soon to see just how they are
faring now, but last report (?5 years ago) they were
doing okay.

However, as tradesmen trained by Tassi moved on, they
started competing with him without understanding what
he was really doing with the mixes, and the quality
and longevity of the patches dropped off markedly.

So much so that there is little point in bothering
with them any more.

What was Tassi's secret?  Quite a few things, I
suspect, including UV stabilisers, low epoxy to sand
ratios (1:10, 1:15, even 1:20), and careful selection
of sand colours to get good colour matching.  He also
was not a fan of face mixes.

Of course, what was happening at the interface was
another story.

But then I had a meeting over coffee with another
stonemason this morning (6am to be precise).  He was
telling me that they used to have a batching kit for
patching that they took to every job.  It contained
small samples of their standard mixes (about 50 all
up), along with a recipe book, and batching tools
(vessels of varying sizes).  All of the masons that
did patching were obliged to use this kit so that
mixes would always give a similar result.  He also
said that where their patches were installed in a
sheltered (read shaded) position, these patches were
still performing well.  However patches in direct
sunlight started to erode within 5-10 years.

Anyway, this is the Australian background.  Keep
thinking it would be good to research patches and
check out their performance ... and I believe that
another organisation has done that to some extent
(although whether the information will ever be shared
is another matter).

Hope this answers your question.

Cheers

david west

> From: Michael Edison [mailto:[log in to unmask]]
> Subject: Re: Sandstone and Epoxy
> The use of epoxy based repair mortar for exterior
> sandstone repair is
> inadvisable for a number of reasons that have to do
> with compatibility. The
> most significant issues are related to thermal
> expansion, moisture and
> modulus of elasticity. Basically, even if you are
> careful to formulate an
> epoxy mortar for sufficient vapor and water
> transmission rates (which is
> possible), it will still tend to distress the
> surrounding stone as
> temperature and moisture content change due to
> inherent differences in
> response to these environmental conditions.
>
> Exterior use of epoxy with masonry in general should
> be limited to those
> situations where the effects of thermal expansion
> and moisture are not as
> critical. The concrete repair industry learned this
> lesson the hard way a
> couple of decades ago.
>
> Mike Edison
> Edison Coatings, Inc.




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