Unfortunately, as I prepare more and more of my home's exterior surface for
painting, I think I am finding a 'home construction deficiency' of a kind.
Some of the trim seems to be made not of wood but something like a thick
cardboard-y wall board. (Insulation board? I think it's that black, like
3/8" thick board that is ordinarily just under the wood or vinyl siding.)
The paint has adhered to it well in some places, to the point you couldn't
tell it was junk. In other places, the paint is peeling (though it sands off
nicely, along with the underlying material!). When I hose certain parts of
the trim down, they appear to absorb water pretty well. (Fortunately I live
in a very dry climate.) But jeeze this stuff is great food for termites,
carpenter ants, etc. Or better food than wood, right? I certainly can't
protect it with a coat of paint the way I could protect wood.

The builder most likely took a short cut (some ten years ago), right? I've
been in the house two years. Had the home inspection and everything. I never
thought to check something like this. OTOH, I'm in a cookie-cutter
neighborhood. All the houses were built about the same time, with very
similar styles. Everyone probably has the same junk. No one's house looks
awful. But I am not confident about how well this stuff will hold up.

Should I tear this stuff off (and it might be every piece of trim, vertical
and horizontal), go buy some board at Home Depot etc., then paint?

I'm somewhat handy with a saw (I have a circular saw). I can hammer nails
competently...

Pardon my naivete on this subject. I'm googling simultaneous to making the
inquiry here.

Painting novice update:
Per my thread of a few weeks ago, I have been preparing all of the exterior
of my house for painting and acually painted a good deal of the back porch.
Looks great! Love that Sherwin-Williams "Duration." SW's clerks were
great--not pushy and happy to make suggestions when asked.

The siding is very rough-hewn, by design, so I'm having more luck applying
it with a "coarse" roller.

"Elle" wrote
Unfortunately, as I prepare more and more of my home's exterior surface
for
painting, I think I am finding a 'home construction deficiency' of a kind.
Some of the trim seems to be made not of wood but something like a thick
cardboard-y wall board.

Correction: There is a definite, pronouned grain pattern in these trim
boards. Knot patterns are on them. Yet it still looks like highly compressed
cardboard on the sides where the paint has come off. Plus, like 99% of the
wood siding is in good shape (apart from needing a nice paint job), but only
about half the trim is in good shape. The old paint peels more from the trim
than it does the siding.

Maybe because the edges of the trim are exposed to water, so it soaks the
water up more readily?

All experience welcome.