I'm almost ready to start rendering the area between the fireplace opening and the surround. I will be burning logs/coal during winter. I intend to use lime in the mix as this will supposedly reduce the chance of cracking. After using the search facility on here I am more confused than ever!. Do I not need to use cement,just lime and sand?. What mix would be best to use,3:1?. Is building sand preferable to sharp sand?. Any advice would be most appreciated.