All you're doing with the coating/painting/drylining is trapping everything that's already well established. It will solve nothing, just delay the inevitable, while continuing to spread in through your house. If it's a 2 storey house the chances are it may have got to the ceiling joists, rafters, etc through the wall plate. More than likely you've got timber windows but maybe not. You need a good builder to have a look at this, maybe an engineer, etc. It looks like the plaster will certainly have to get taken down as a 1st step, it's at that stage you'll find out what sort of penetration has taken place. Not good me telling you now, but delaying it any further will only add to the whole unfortunate business.