rendered old stone house with OPC - learning expensive way

I was doing some quick research on the web to find the best ways to redo the facade of my new/old stone house, and currently I'm almost in tears after learning few things.

Thing is simple, but extremely problematic - I renovated old (about 400 years) stone house this year - small one about 80 sqm footprint - just ground floor As house walls are partially bellow the ground level I consulted several 'specialists' in order to find the best way to stop water penetrating it.
Following some of those advices I ended up rendering all but one of it's old stone walls on the interiour with just OPC/sand render - no lime at all. It's done as base layer for additional cement based water insulation. Just tonight, 6 months after I moved in my newly finished interior (insulation seems to be holding great for 6 months now), I learned that use of OPC like that could be devastating to my home.

Just to give you few basics - masonry is double layer - about 80 cm thick in total, mostly limestone, originaly built with lime/sand based mortar.

What to do, and how urgently it needs to be done in order not to ruin what generations before me maintained and cherished? I would appreciate something less violent and something giving me some time - as I just moved in and that's my only home.

Opinions?

Dalmation; you are correct to be concerned about what you have done to your building, by rendering the "ancient" , 400 year old masonry walls with an opc mortar. On the surface, the use of an opc, "ordinary portland cement" mortar would seem the best way to go in that it offers a stronger, and less pervious coating, while also offering a substantial surface to affix your insulation to. You were concerned about moisture seepage through the walls. However, these most recent concerns you have had, tell me you have learned something about very old masonry walls. They do need to physically move; i.e. which the lime mortar allows, and moisture also needs to move through them and does not present a problem as it evaporates off the interior wall surfaces. There are some solutions to consider before removing the insullation and chipping out the opc mortar; i.e. removing the opc mortar is the final solution. Consider waterproofing the exterior with a clear liquid silicone either sprayed or brushed on. Or, get recommendation from local mason as to what 'clear liquid water repellent' they might use on the exterior for your situation. (By eliminating moisture from moving through the walls, you will remove most of your concerns about wall deterioration.(Now, there is no way for this moisture to evaoprate what with both the opc rendering and the interior insulation. Finally, if the exterior sealer works, you would be able to leave the opc mortar, and also leave your insulation in place. Good luck.... regards Jerry Janson