My 1917 farmhouse had a patio poured at the exact same height as the
room it adjoined. This allowed water to seep under the exterior wall
and wet the drywall and insulation.

We just has the patio removed. The new patio is going to be about 3
inches lower. We are going to use those flagstone-looking squares
(18") from Lowes/Home Depot. These will be set on a bed of sand with
either sand or maybe marble chips in-between.

We are lucky that the room adjoining the patio has a tile floor that
serves to seal out the moisture that seeps up through the concrete. I
will put some kind of sealer on the newly-exposed raw edge as well.
What I'm debating now is whether or not to put plastic sheeting under
the flagstone. The concrete patio was 6-8" thick so the ground is
very compressed. They used a backhoe to remove the big pieces of
concrete and the ruts held water for 3 days (but it has rained -alot-
here in the East).

I will do all of the appropriate sloping so the plastic will have a
chance to drain at one end. I just can't visualize whether the
plastic would help or hinder moisture (not water) sponging it's way to
the concrete under that room.

Thoughts?

Thanks!