Re: Ellen's elastomeric coatings and "all the crevices of metal shingles"

I've seen satisfactory performance of applied coatings on copper roofs
which had developed "pinholes" in undocumentable locations.  But I have
trouble imagining how thin elastomerics (thin enough to not obscure the
roofing pattern very much) effectively span seams or gaps, especially when
even small movements of the substrate could  tear open the membrane.  That
is to say that if the elastomeric is well bonded to each of two metal
pieces, as it should be, then movement between those two pieces stresses
the inner face of the membrane with zero dimension of tolerance.  The outer
face of the membrane might stretch a bit, but doesn't the inside face of
the membrane propigate into a tear?!  Therefore, I wouldn't expect much
from thin coating seamed material subject to expansion, contraction or
other movement.  Thick sloppy bituminous coatings are another thing, and
that would considerably obscure the pattern considerably.

It's the same principle as for joint sealants that are bonded to all three
concealed faces of the joint (instead of only the two opposed faces).
Movement or opening of the joint would tend to tear open from the inside
out, causing the joint to fail.

I assume coating a shingle roof is a stopgap measure to keep from a more
thorough repair or treatment.

--Jim