Fellow Shadow Watchers,
Now that I seem to be back in touch, here is a
repeat of one of the messages which went astray recently. Mike Shaw
reports that some of his email seems to have gone into a delay loop
recently so please forgive me if the original turns up in time.
Tony Moss
*********************
Subject: Re: ancient dial (stone protection)
Sent: 26/11/01 10:34 pm
To: John Carmichael, [EMAIL PROTECTED]
John Carmichael contributed:
>I am assuming that "water repellent" means an epoxy or polyurethane sealer
>(It could also have been a wax or oil, but I doubt the restorers would have
>used those.) Of course, these are much better reaction barriers than a
>carbon coating. A good sealing job will provide 100% protection against acid
>rain. These sealers will not only prevent water from wetting the surface,
>but since they penetrate deeply into the sandstone pores, they protect the
>interior of the stone as well.
The water repellant for masonry that I'm familiar with is a thin liquid
silicone preparation commonly applied to brickwork and garden ornaments
to make them 'frost proof'. When applied it is quickly absorbed to expel
existing water and prevent further rain soaking in. Without this
preparation, absorbed water will freeze and swell in any small cavities
causing exfoliation of the surface.
This may not be the treatment which has been applied to the dial Frank
Evans mentioned but I think it more likely than any kind of surface film
which might do more harm than good. Our local branch of Barclays Bank is
housed in a 'listed' building of old hand-made bricks which were given a
'protective' coating of some sort of resin about five years ago. This
has now discoloured and flaked away from the ancient powdery surface to
look like a bad case of sunburned skin peeling off. If exfoliating
bricks are treated with silicone it is quickly invisible and the
deterioration is slowed/halted immediately.
Guess why I prefer metal??
Tony Moss
