Mitch, Ken, Leland:

In my opinion, hydrofluoric acid is probably the most serious chemical hazard
in restoration and renovation.  It's danger isn't as an acid.  In fact, it's
acidity is so weak that it is fairly ineffective.   But, this chemical can
easily cause severe illness, loss of limbs, and death.  How?  The HF starves
human cells of essential calcium.  It can kill it's way to the bone in your
arm or your leg, where it usually stops, causing one to lose a limb but not a
life.  Or, if you splash it on your chest, it can just drill to your heart,
whereupon the heart muscle dies just before the mind.

Why do I know all this about HF?  I've been trained in it's hazards.  I've
used it for whole-rock chemical analyses and for separating pollen from clay
and silt.   I've instructed my chemist employees how to use HF safely and
responsibly.  I've worked for a company (Vulcan Materials) that made
hydrofluoric acid.  In my opinion, HF should only be used in a fume hood with
rubber gloves, a chemical apron, and goggles.  Why anybody without a wish to
die a horrible death would use HF in the open air without wearing a full set
of protective equipment is a mystery.  Maybe they are damned fools; maybe
they are the low bidder.  Maybe the boss just figures that laborers are
expendable.

I hope that everybody who has or intends to work with HF has calcium
gluconate gel and syringes in their medical kit.  These are essential to
counteract the effects of HF exposure.  I bet that nobody does.  Perhaps I
shouldn't be so cynical.

On the plus side of HF, it works fairly well to dissolve iron stains and dust
deposits consisting of quartz silt and fly ash.  It also brightens granites
and other quartzose rocks.  It dissolves the quartz and silicate minerals
preferentially at the surface fractures that make a stone lighter than it's
intrinsic color.  If the rock contains calcite (calcium carbonate) it reacts
to form fluorite (calcium fluoride).  This precipitated mineral slightly
protects the surface.

FYI, the Lincoln Memorial is made of Yule marble from Colorado.

Steve Stokowski
Stone Products Consultants
Building Products Microscopy
10 Clark St., Ste. A
Ashland, Mass. 01721-2145
508-881-6364 (ph. & fax)
<A HREF="http://members.aol.com/crushstone/petro.htm">http://members.aol.com/crushstone/petro.htm</A>

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In a message dated 5/8/03 5:24:01 PM Eastern Daylight Time, [log in to unmask]
writes:

> Are any of you stone guys familar with Klenztone cleaning chemicals?
> One of there products uses a special formula of floride salts.
>
>
> Mitch,
>
> I'm quite familiar with the materials and have used them to good effect but
> am a bit peeved about their lack of truth in advertising. Despite the fact
> that the advertising states that the chemicals contain no acids the
> flouride salts turn to hydroflouric acid when they encounter water.
> According to my materials handbook hydroflouric acid is used in cleaning
> cast iron castings by dissolving the sand from the castings. What this
> means for sandstone I think should be self evident. What it means to the
> Lincoln Memorial, I assume of granite, is possibly less shocking. I would
> certainly NOT use it on limestone or marble. What gets me with suppliers of
> chemical cleaning solutions is that they will say that their materials were
> used in this place, or that, but they will not tell you the truth of the
> long term results, or what is really needed to know in order to do no harm.
> I feel that Klenztone is the worse of any in this regard. In the past I've
> asked Klenztone (directly asked of Klenztone and NOT of any of their
> suppliers who usually have no idea what they are selling) to give us names
> of buildings where their products were used in order to revisit the
> locations in order to determine if the masonry was acid burned, or not. It
> is when manufacturers are not up front with their information that I begin
> to suspect ALL of their marketing hype. The "no acids" caveat is one that
> will catch out preservationists seeking a non-acidic cleaning
> methodology... well, when you use their product it does look good. It has
> to be used with the same care, skill and attention as would be used when
> cleaning masonry with any acidic cleaner. But if your chemistry and science
> in the beginning exluded the use of acids, then I think it a really lousy
> deception to pretend that acids are not being used with Klenztone.
>
> My first phone conversatin with Martin Weaver was to ask him about
> Klenztone, and my naive remark that the material contained no acids and I
> wanted to know how it could possibly clean masonry. His comment, in brief,
> was that he did not know of any masonry cleaners that would not contain
> acids. I went away imagining that he would think I was a complete dolt.
> Some time later I spent an afternoon drinking ale with him and Bobby Watt
> in a dive in Ottawa and found out Martin is a very very nice guy, a bit
> hilarious in humor and an out-of-the-box free range nut case.
>
> ][<en