Okay I know this sounds bizzarre but it really works! To get bluetac off, without ruining your wallpaper is simple. Dab some toothpaste on each of the blobs of tac and allow it to dry, then gently sponge off with a damp cloth after a day or so. Simple! Toothpaste for some reason dissolves the bluetac, I don't know why it works, it just does.