A thought just occurred to me which might be germane to this
discussion. Perhaps someone familiar with how latex paint works could
comment.

My understanding is that latex paint binder consists of monomers in
water solution.

When you apply a coat of latex paint, and the water dries, the monomers
come out of solution and begin to bond together into polymers. This
bonding action forms the strong film. Once the polymers form, they are
no longer water-soluble. That's why the film is water resistant, even
though the original vehicle was water.

Now, what happens when you apply a second coat of latex? Obviously the
process repeats itself. BUT, in addition to bonding with EACH OTHER,
do the monomers in the second coat ALSO bond EQUALLY EFFECTIVELY with
the polymers in the first coat, to create one seamless film (assuming
the first coat was kept clean) ? Or, is the bonding between the
monomers of the second coat and the polymers of the first coat only
PARTIAL, so that what you get is two SEPARATE films which are bonded
together, but the bond BETWEEN the two coats is not as strong as the
bond WITHIN each coat?

If the latter is true, it would explain the difference between boards
one and two in the example I gave in an earlier post. The first and
second boards would have the exact same total film thickness, but the
first board would have fewer, thicker layers; and the second board
would have more, thinner, layers. What this means in practical terms
as far as the quality of the paint job is still arguable I suppose.