From: M. P. Edison [mailto:[log in to unmask]]
Sent: Wednesday, October 30, 2002 6:04 PM
Subject: RE: Coating analysis interpretation
Dan,
Additional comments on your response are below.
Mike E.
> I would tend to agree with you on the face of it, but from my
inspection
> of the material in situ, it struck me as much MUCH harder than one
would
> expect a really thick coat of latex paint to be. There was another
> product back in the mid-80s, "Siding in a Can," that we were able to
get
> specific product data for, and it _was_ a thick latex paint. This
> material presents a different appearance than that product did. My
> nagging intuition, which admittedly is all I have to go on, is that
> "Spray on Siding" is more akin to a petrochemical-based sprayable
> plastic coating. It had no give at all under the Official Fingernail
> Press Test, which I would expect a thick latex to have some give.
> Perhaps my sense of the hardness of latex is at error.
Hardness is a tricky thing to evaluate, sometimes. For one thing, it
has a lot to do with temperature. Polymers are often characterized in
terms of "Tg", the glass transition temperature. Each polymer has a
specific temperature at which it changes from a somewhat flexible,
rubbery material to a hard, glassy material. The liquid siding product
reports an elongation of 150%, presumably at or near room temperature.
But if it has a Tg of say, 55 F, it might seem awfully hard on a
chilly late October day.
Fillers also have a big influence on hardness. Take some fairly soft
paint and add some sand and you may get something that feels
relatively hard.
As for latex vs. "petrochemical", I assume you are thinking of the old
solvent-borne industrial enamel coatings we used to see. Latex
polymers can be hard, soft, flat, glossy or anywhere in between, and
it is pretty hard to tell some of them from the old solvent-borne
coatings any more. Acrylic polymers are derived from natural gas,
regardless of whether they are acrylic latex or dispersed in solvent
or molded into tail light lenses for your car.
>
> I've never thought of paint as decorative, and it steams me when I
see
> painters treat it as a decorative color change only. It is first and
> foremost a protective coating, which has a collateral benefit of
being
> able to have color applied to a decorative end. But the idea of a
> continuous coating, with care exercised in ensuring that caulk is
well
> done, that the coating is seamless and adequate in thickness for the
> purpose of protecting the substrate from water infiltration, seems to
> elude a lot of people. So I guess the reason for a thick coating, if
in
> fact it has vapor permeability, would be a higher percentage
assurance
> of adequate protection.
Film thickness is not the only way to achieve film integrity.
Different materials have different chemical structures, so 1 or 2 mils
of self-crosslinking polyurethane (0.001 - 0.002" thickness) can be
far more waterproof than 5 to 8 mils of a typical acrylic latex, not
to mention far more chemical resistant. Vapor permeability also
relates to film integrity and some breathable coatings rely on lots of
film imperfections to achieve that permeability.
>
> So then I get back to the failure mode discussion and the
reversibility
> issue; if it's plastic and it cracks, what the hell do we have then?
And
> what do we do? Does it scrape off like paint when it finally reaches
its
> point of adhesion failure? Only time will tell.
Mode of failure is an important observation in accelerated weather
testing. Did it chalk? erode? crack? peel? swell? yellow? The liquid
siding guys don't tell us, they just say "Excellent". If the coating
is reasonably UV stable, the expected mode of failure would be slow
erosion. If it embrittles with age, it could be a much less tolerable
change.
Edison Coatings, Inc.
M. P. Edison
President
3 Northwest Drive
Plainville, CT 06062 USA
Phone: (860)747-2220
Fax: (860)747-2280
email: [log in to unmask]
Internet: www.edisoncoatings.com
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