"Ether Jones" wrote in message
ups.com...

The cracks I am talking about are not large cracks that could be
caulked. I'm talking about many fine splits in the wood; of the order
of the thickness of a piece of paper. The unthinned paint simply
cannot get in there thoroughly, no matter how aggressively I brush it.
And, as it cures it leaves pinholes where the splits are; pinholes
where water could get in.

What you're looking for is a "block filler" paint/primer.