Leland Torrence <[log in to unmask]> wrote:

> But it lasted the first 100 to 150 years, that
> seems pretty good.  Plus,
> the sand is essentially the same fabric as the
> original.  I don't think the
> original masons did anything special before mixing
> other than a wash.  Do
> you know otherwise?

> I understand the salt issue, but have
> experienced little evidence that
> it has a significant play.  I have noticed a ton of
> efflorescing on every
> brick pointing job at Yale where the sand has been
> carefully spec.'d.

Is this heresy?  Boo. Hiss. Everybody (?!) knows that
it is just plain commonsense not to use beach sand
because the salt will cause the mortar or concrete to
break down.

Yeah. Right.

Does this fit into the same pond of knowledge that
contains the belief that you should never use acid on
sandstone because it accelerates decay? Yes, strong
acids will do that.  But well-diluted acids?  I'm
happy to discuss that particular topic further in
other posts.

However, my point is that whilst THEORY says that salt
in sand for mortar is bad, because lots of tests have
shown it to be so, and because we have seen
deteriorating mortar that originally contained beach
sand so it is convenient to blame the salt, do we
actually have control testing to show that the
original salt content is the real problem in these
cases.  I suspect not.

Therefore I tend to feel that whilst in SOME cases,
the use of unwashed beach sands may have been a
significant contributing factor to early deterioration
of mortar or concrete, in OTHER cases, it may have had
little or no effect.

I believe that broad generalisations like this are
definitely useful at times, particularly when dealing
with people whose concern is solely the short-term,
bottom-line.  However, such generalisations can mean
that reasonable alternatives, which may indeed be more
AUTHENTIC, are not explored as valid options.

I'm sure we could all find numerous examples of such
things, in many different sectors of our profession.

As Leland asked, thoughts?

david

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