We have installed a liner and still have tar seeping through the bedroom wall...how do you fix that??

Old stone farmhouse where previous owners burnt anything in the Rayburn (ie pieces of old kitchen worktop) we now have installed a liner in the chimney, but are still getting tar dripping down the walls, especially in the bedroom. do we need to take the plaster off back to the stone & clean?? It also drips on the Rayburn in the kitchen......the Rayburn hasn't been lit for weeks so its not heat but we have had lots of rain!