"stuart noble" wrote in message
...

As to why paint blisters and
peels on the outside lapboards of a painted house. What's happening is
that
without vapour barriers and or adequate ventilation moisture condenses as
it
meets the cold 'within' the exterior walls and then pushes the paint off!
Houses finished with permeable stain permit that moisture, some will
always
occur, to 'breathe' out through the walls.

A lot of issues here which I'm not qualified to argue about, but all paint
allows the passage of water vapour, while hopefully resisting water
droplets. Some figures were posted here a while back which suggested that
surface coatings offer virtually no resistance to vapour. I wonder whether
paint would peel off new lapboards as easily.
I think wood just deteriorates with age and becomes porous to the point
where it cannot support a coating.

Oil based paint on bedroom ceilings will certainly act as a vapour barrier.
Not a full one, but will certainly help.