Subject: Spot Etching
Date: Mon, 25 Mar 2002 13:24:26 -0700
From: "Jonathan E. Dongell - Whitestone Cement Co."
To: Bob Tomlinson

Bob,
I would like to respond to Jerry's letter, I understand that he is
trying to bring balance to the discussion at hand. And, I am aware that
our Research Committee has been disbanded. However, I believe that the
following must be said to set straight for the record. In terms of what
Jerry referred to in the minutes about what he thought, or possibly
misunderstood me to say, and also in terms of what I believe is the
problem in general.

I think, that in an attempt to be fair beyond all reason, the National
Plaster Council has put itself in a situation where we have forced
ourselves to discuss the ridiculous.

"Spot Etch" is very difficult to explain, even harder to understand, and
almost impossible to define, or to prove its' every occurrence. Not
because we don't understand the process by which it occurs, but because
it is near impossible to define every environment or circumstance that
allows spot etch to occur, or how each contributes in some way to its'
occurrence. In other words, there is no single experiment, definition,
or explaination that works for every possible situation, and every
possible variation of its' occurrence.

However this does not mean we are left helpless in this…..Other plaster,
concrete and cement trades/organizations/associations have "etching"
defined very well. How did they deal with it??? They explain the cause
of "etching" and not "spot etching" and not "highlighting". This easily
allowed for a cause/relation to be developed. We know what causes
etching, in general. There is nearly 100 years of documented research
papers and books which discuss etching. It has already been done for
us. We simply need to refer to these references and move on.

Otherwise, if we are going to try and explain why we see spots and
lines, for which we have no constant or definite method to prove or
explain every possible occurrence, we will be fighting this forever.
Why??? Because it is nearly impossible to explain, or to know, every
contributing factor that must occur, or how every factor contributes to
the occurrence, or to what extent each factor must contribute in
relation to the other contributing factors. In other words, we can't do
it……. The potential variations are too many. Every field situation is
slightly different. And therefore, an argument can be made ( and
obviously is being made) that any conclusion we come up with, holds true
for only that circumstance that we were dealing with during our
experiment, to come up with our conclusion, and nothing more. In other
words, we will have done a lot of work for nothing. Because it will
have only proved one of the scenarios.

If we define "etching" of the plaster in general, and we have a "primary
cause" section and a "possible contributing factors" we can avoid all
the BS(backsliding) and we will be technically and politically correct.
And more important, stop any more of this discussion that just moves us
off track.
Example: (not to be used. I am just writing these words)
Etching: The removal, by degradation, of the surface of the plaster.
Primary causes: Friction ( such as a pool cleaner rubbing)
Dissolving: (such as an imbalance between
the pool water and cementitious plaster)
Dissolution: ( such as a weak plaster from
too much water in the mix design or from re-tempering plaster surface
that is already final set)
Contributing factors: Aggressive chemicals, dillution of the cement at
the plaster surface, etc…

The hard trowel surface, calcium chloride, or excessive hard troweling
do not come into play at all because they do not contribute to etching.
In fact, it can be shown that they decrease etching. In fact, this is
why we see spots and lines in areas, and not etching across the entire
surface of the plaster, because the density that the hard trowel creates
at the surface, also prevents aggressive water from deteriorating the
plaster surface as quickly. Unfortunately the hard trowel surface is
hand troweled and therefore not 100% consistent across the surface in
its' uniformity and density. But, if we continue to insist on defining
"spot etching" and "highlighting" then the these three must be added to
the possible contributing factors, because they do contribute to how
spot etching and highlighting are formed. They are not causing it. But
the opposition is correct (though I believe unfairly so), when they say
that these three are contributory factors to why "spot etch" and
"highlighting" forms and looks the way that it does…..

Does this make sense?

Please give me your thoughts on this.

Jonathan Dongell