I have to add that salt is not good for stone -- any stone -- as it
crystallizes down in the little pores and breaks the stone apart. This
is one (of many) reasons that Portland is bad for building stones; it's
why you dont use Chlorox bleach to clean tombstones; it why you dont
want to apply salt to stone steps or near stone or brick buildings. It's
very damaging to stone. Remember the kindergarten experiments where you
grew salt crystals? That's what happens when salt gets inside stone...it
grows and displaces the aggregates and binders.
 
It may be that you could use it during the incidence of snow but it'd
need to be washed off thoroughly after that (and who's going to go to
that much trouble -- lack of maintenance being the biggest enemy of
building materials). I doubt there's any coating that would weather at
the same rate as marble, allowing it to breathe and dry out as it needs
to. This is a good question of a stone conservator. There was an
excellent one at Prosoco labs. Maybe they've replaced her with an
equally excellent one. But ask at Columbia or U Penn or other programs
where architectural conservation studies are ongoing.
 

Camille Agricola Bowman 
Easement Technical Advisor 
Tidewater Region Preservation Office 
Department of Historic Resources 
14415 Old Courthouse Way 
Newport News, Virginia 23608 
Tel: 757-503-1549 (NOTE: New Number) 
Fax: 757-886-2808 

 

________________________________

From: The listserv where the buildings do the talking
[mailto:[log in to unmask]] On Behalf Of
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Sent: Wednesday, March 03, 2010 2:29 PM
To: [log in to unmask]
Subject: [BP] Salty Steve makes piquantly marbled waves on ConsDistList
...


------------------------------

Date: 24 Feb 2010
From: Barbara Appelbaum <aandh [at] mindspring__com>
Subject: Clearing snow and ice from marble steps

On behalf of Christopher Gray <methistory [at] aol__com>, Steve
Stokowski writes

>Barbara Appelbaum <aandh [at] mindspring__com> writes
>
>>A client of ours has asked about the problem of clearing snow and
>>ice from marble steps.  She knows that salt should not be used.  Is
>>it possible to apply coatings in advance that will mitigate the
>>possible effects of salt, or is there something else--ash or sand,
>>perhaps--that is not harmful to marble?
>
>I cross posted Barbara's query on Bullamanka-Pinheads, a listserv
>oriented towards architectural conservation, and Steve Stokowski
><crushstone [at] aol__com made the piquant remarks below (reproduced
with
>permission)
>
>   "Apparently she doesn't know as much as she thinks she  knows.
>    Just why shouldn't salt be used on marble steps? No good reason
>    at all, she may have half read and retained less a newspaper
>    article about salt use on roads. The issue with salt, and I am
>    specifically talking about NaCl, is  that it increases the rate
>    of corrosion of steel, specifically steel embedded  in concrete.
>...
>   "So, unless the marble steps are pinned together with ferrous
>    pins, she should go ahead and use NaCl to deice the
>    steps ...

I don't believe that salt should be sprinkled around by the ton.  It
ends up in lawns, in gardens, and in run-off that goes into storm
sewers.  If it's applied to the steps of buildings, it ends up on
floors. The responses I have gotten either suggest more manual
removal of snow before it packs down and turns to ice, or the use of
defrosting liquid that is mostly methanol.

Rather than discuss "piquancy,"  I will say that I want to thank the
thousands of people who log onto the list, bravely admitting their
ignorance on some topic or other, and who then graciously and
generously supply us all with information we couldn't easily get
anywhere else, and all without rancor or snide remarks.

Barbara Appelbaum
Appelbaum and Himmelstein
444 Central Park West
New York, NY  10025
Conservation of Works of Art
212-666-4630

------------------------------

Date: 27 Feb 2010
From: Andrew Thorn <artcare [at] iprimus__com__au>
Subject: Clearing snow and ice from marble steps

On behalf of Christopher Gray <methistory [at] aol__com>, Steve
Stokowski writes

>Barbara Appelbaum <aandh [at] mindspring__com> writes
>
>>A client of ours has asked about the problem of clearing snow and
>>ice from marble steps.  She knows that salt should not be used.  Is
>>it possible to apply coatings in advance that will mitigate the
>>possible effects of salt, or is there something else--ash or sand,
>>perhaps--that is not harmful to marble?
>
>I cross posted Barbara's query on Bullamanka-Pinheads, a listserv
>oriented towards architectural conservation, and Steve Stokowski
><crushstone [at] aol__com made the piquant remarks below (reproduced
with
>permission)
>
>   "Apparently she doesn't know as much as she thinks she  knows.
>    Just why shouldn't salt be used on marble steps? No good reason
>    at all, she may have half read and retained less a newspaper
>    article about salt use on roads. The issue with salt, and I am
>    specifically talking about NaCl, is  that it increases the rate
>    of corrosion of steel, specifically steel embedded  in concrete.
>...
>   "So, unless the marble steps are pinned together with ferrous
>    pins, she should go ahead and use NaCl to deice the
>    steps ...

I do not agree entirely with the advice of Mr Stokowski, both in
terms of the impact of halite on marble, and in other comments made
about steel and concrete. I do agree with the general sentiment that
halite does not necessarily cause damage to the degree that people
assume, however I would not then suggest that it is not a serious
threat or that it is less damaging than other salts. Sound
conservation practice demands that we remove all risks, rather than
advise that the problem is not as great as we think it is. There is
ample evidence, probably millions of examples, where halite can be
directly linked to damage, and to suggest that there are other salts
that may be more damaging is irresponsible comment. Certainly the
repeated application of halite and its absorption into the marble
will inevitably lead to impact. This impact will be active during
the thaw months. It is the conservator's role to advise on
completely safe approaches, such as the second advice that ethanol
may be the solution. Warming is another, as is covering when not in
use. I am not proposing these as solutions but each is infinitely
less threatening than the notion that halite is not as bad as some
salts the commentator can name, therefore get over it and get a
life.

The commentator also states that halite "increases the rate of
corrosion of steel, specifically steel in concrete". This may be a
semantic error but is simply not true. Halite will promote the
corrosion of steel in any surroundings provided the pH of the
surroundings are favourable. Fresh concrete inhibits this and it is
only fully carbonatated concrete, where the pH has dropped to around
8, that will no longer inhibit corrosion. Mild steel in concrete
will not corrode faster necessarily than it will embedded into any
other material, although this is a bold statement that can easily be
contradicted too. Having said all of that the relationship to
halite, steel and concrete has little bearing on the impact of
halite on marble.

So my advice is to retain the caution expressed about the
undesirability of halite as a de-icing approach. This is sound
conservation practice and what we are trained to do. The suggestion
that you have half read a newspaper article is somewhat
condescending and I would advise Mr Stokowski to read the other half
of the technical literature on halite damage to marble.

Andrew Thorn
ARTCARE
614-1926-9326
613-9326-9326

------------------------------

Date: 24 Feb 2010
From: Grace Wever <grace [at] realwest__com>
Subject: Clearing snow and ice from marble steps

Barbara Appelbaum <aandh [at] mindspring__com> writes

>A client of ours has asked about the problem of clearing snow and
>ice from marble steps.  She knows that salt should not be used.  Is
>it possible to apply coatings in advance that will mitigate the
>possible effects of salt, or is there something else--ash or sand,
>perhaps--that is not harmful to marble?

Here is a response to the question about the effects of using salt to
clear snow and ice from marble steps .  This information is based on our
experience over several years with the effects of salt exposure on
marble
flooring on cruise ships.  On a number of ships, marble flooring has
been
installed near doors that opened directly onto deck areas.  Saltwater is
tracked in regularly by passengers and staff, and also blows in during
inclement weather when the doors are opened.  The saltwater penetrates
into the marble, and dries.  The salt then "attracts" water from the
air,
and the resulting osmotic pressure from the continual build-up of water
causes the marble to disintegrate.  The resulting pitting is very
unattractive.

There is a similar phenomenon that has been reported with
naturally-occurring granite in the vicinity of the great Salt Lake in
Utah--granite boulders have been known to actually explode, due to the
continued buildup of salt and the resulting take-up of water, creating
high pressures.

There are commercial treatments for marble and granite that provide
protection against slipping; but they need to be applied regularly, as
they are rather superficial, and are removed by foot traffic.

Grace Wever, Ph.D., Montane Associates


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