Only one method from shipbuilding, repair of delaminated sandwich components. Limit the delaminated area by tapping, mark it with a felt-tip pen. Drill at two outer points. Obtain a single-use syringe from a doctor, without a needle. Draw up liquid epoxy, slowly inject it at one point until it comes out at the other drill hole. For this, choose resin with slow hardener. And a resin type as thin as possible. Whether this also works with facade plaster, I do not know. EP sticks practically everywhere, but it is expensive. Available from Vosschemie, Uetersen. Bacuplast. Polyesterzentrale Lübeck, to name just a few shops. By the way, EP only works if insulated with polystyrene. It may dissolve other foams. Karsten