I have to say that I've never seen anything like that before. Has done much damage inside the house hdl986?
I once read about romneya coming up through floorboards in a very old cottage. I would imagine it must be strong enough to pierce lime mortars.
@hdl986 It may seem strange but you could have problems propagating it. It does not establish very well at first even though it can be invasive.
I would be worried about water finding its way through the holes in the mortar after the plant is killed.
@hdl986 This is a friends painting of R Coulteri it's petals are like tissue paper. Not sure where she painted it but a house nearby with a long drive had some growing in a border near the gate for years. The plant was 6x4ft, it would have hundreds of flowers stunning next to a blue sky .Suddenly one spring it had gone. I have occasionally seen it for sale in the UK but not with any warning as to what it is capable of doing! I hope your renovations go well. Maybe you have some more unusual plants in your garden? Your Romneya was probably planted by a plant enthusiast who sadly did not know it was invasive.