Friday, July 27th 2012
Prefabricated, factory-built fireplaces typically have lightweight concrete block rear walls. It is very common, over time, for these blocks to develop hairline cracks. If these cracks are not big enough to insert a pencil eraser into, they probably do not pose a hazard. Remember, there are two or three layers of metal behind the blocks, so there is no danger of sparks finding their way through. If the blocks are very badly cracked and crumbling, they should certainly be replaced. You will need to know the manufacturer and model number of your fireplace (typically there will be metal tag somewhere inside the fireplace with this information).