Having removed a 1980s gas fire from the living room of my early-Edwardian property, I discovered the floor beneath the hearth and the base of the walls around and inside the fireplace were damp. It seemed to be where the hearth had been fitted and mortared (not sure if this is word) up to the brickwork and a vermiculite screed placed over the original solid floor. I suspect this is because the mortar and vermiculite breached the slate damp course and prevented the area from “breathing”. Does this sound about right? Since the hearth and vermiculite has been removed, the walls have dried out significantly, although there is still dampness to the solid floor (not what it was though).
Now, I am looking to fit a refurbished original cast iron insert (complete with back) and wooden surround. I was intending to leave the area behind the insert clear, so that the area can continue to breathe and so that any fire would also help to evaporate continuing residual dampness in the floor Again, I suspect this is what may have happened historically, but I am aware of much “advice” now that says the area behind the fireplace must be backfilled (depending on the advisor, with anything from hardcore, to rubble, vermiculite/cement. What would be your advice?