I hope the moisture is just from the crawlspace never having had enough
ventilation; my neighbors houses, just 20-30 ft away on either side and
the same age, both have very dry crawlspaces. My house has very wide
eaves and the soil almost never gets very wet next to the foundations.
All run-off is into drains, and the ground is sloped away. It's at the
base of a hill, but there are berms with drainage across the hill.
My thought was that sand would, as you suggest, give the moisture
somewhere to collect, plus it might be a "vapor pre-barrier" before the
plastic. If I have the sand put in and then plastic put down right after
the mildewcide etc. is sprayed on, my theory is that maybe there will be
less opportunity for musty mildew to grow under the plastic.
Until the crawlspace has had a few months to air out with the new vents,
I didn't want to go to the next step of looking at drains in there until
I know that the cleanout & new vapor barrier didn't do the trick.
Of course, I haven't the foggiest how I might get the sand in there or
spread it ... maybe get a couple of large, low, garden wagons and drag
them around with pulley & ropes. Is there some machine that could blow
sand instead of bark mulch?