Wall Repair

[dik]

I’m looking at providing a repair to an existing wall, approximately a 4’x4’ patch. The existing wall construction (from the outside to inside) is precast concrete panel, parging, 1-1/2” closed cell rigid insulation, parging (or 'scratch' coat), finished plaster and paint.

My patch consists of adhering extruded polystyrene rigid insulation to the precast and adhering exterior drywall to the rigid insulation. The joint will be finished using a water resistant jointing compound with a fiberglass mesh jointing tape. I’m planning to use a polyurethane caulk to ‘connect’ the two rigid insulations (exist and new). I’m relying on the caulk and rigid insulations to provide any vapour barrier. The patch and joint will be painted using an acrylic latex paint.

Does anyone see any hiccups with this approach, in particular with the ‘lack’ of vapour barrier? Environment is humid, but this can be mechanically controlled.

 

[shobroco]

How big a temperature differential will the interior & exterior see? That will drive the moisture & affect the system more than anything. EPS & closed cell foams usually meet the minimum spec for a vapour barrier so if they are sealed together there should be no issue. If you are concerned about the new insulation being more pervious than the old, use a trowel-applied adhesive/VB & butter the edges of the new EPS too.