I am about to Sandtex the outside of my bungalow but there is a - according to a very old surveyor's report - 'fracture to an external wall caused by thermal movement rather than structural movement'. It is a very very narrow crack about three feet high, and in the past I have channeled out a 'v' shape and filled it with concrete but it has appeared again. Before I paint, is there anything I could repair this crack with so that it does not appear again? It is vertical, underneath a window and it is so narrow I can't even get a pin in the crack. Thank you for any help.