In uk.d-i-y, Christian McArdle wrote:

Would a thick lump of plywood be stronger than chipboard?

[to support a hot water tank] I'd *much* prefer decent (but not madly
expensive) ply to chipboard. The "WBP" quality - nominally meaning "wash
and boil proof" of midpriced hardwood ply will shed hot water, should
you ever get a drip you don't notice, rather well (a quick coat or two
of varnish or Danish Oil won't hurt). Chipboard, even bathroom spec
"moisture resistant", is *not* what I'd want 180kg of 60-degree water
resting on ;-)

Stefek (who's just spent the whole weekend building a wheelchair/impaired
mobility ramp out of two sheets of 18mm WBP hardwood ply, (nearly 50
cm of height to cover, so two sheets totalling 4.8m length needed to
give even a 1:10 slope) and is impressed by its rigidity even before adding
three 6.5cm deep ribs down each length. Oh, if anyone's in Bristol, the
reason it rained last night from about 10pm onwards is that I'd put the
next coat of varnish on at about 9pm... some rather more vigorous
rubbing-down needed before tonight's coat goes on, dammit.)