Concrete guttering

[Phil1p]

I have concrete gutters. These are essentially large concrete blocks spanning the cavity at the top of the wall. The outside forms the gutter and on the inside they protrude into the bedrooms. They are basically a large cold bridge and so on the inside I get a build up of mold and mildew. I intend to box-in the inside edge with plaster board then skim and paint.

My questions are:
Will this stop the mold forming on the inside?

If so:

should I use a polystyrene backed thermal board or a foil backed vapor board?

Any advice is warmly welcomed, Thank you for your time

[welsh brickie]

use polystyrene backed plasterboard, that should prevent it

[Phil1p]

Thank you for the reply, i shall let you know how it goes