What Are These White Crystals Growing On My Brick?

Recently, while visiting some friends, they asked my thoughts about some fine white crystals growing on the decorative tile around their fireplace. They have propane gas logs in their fireplace so the flue is supposed to be shut. This substance is called "efflorescence" and its a salt crystal that forms when water soaks through all kinds of masonry (efflorescence will also form on drywall and other surfaces penetrated by moisture) to the surface and dries. The water leeches out the salts from the masonry and when it reaches the surface the water evaporates leaving the salts behind. A little is normal, but excessive efflorescence will lead to the deterioration of the masonry and mortar if left unchecked, which is especially harmful if its taking place along your foundation, and is an indication of a moisture problem that will only get worse if left unchecked. Excessive efflorescence around a fireplace or chimney may be a sign of a compromised flue liner, so have a chimney inspector check your chimney for cracks or deterioration in the flue liner.

If you use your fireplace heavily, its recommended to have it serviced professionally every year. Every other year is adequate for a less frequently used fireplace.

My friends problem was two-fold. Their chimney is open, so rainwater falls unchecked into the chimney, and their damper is old so doesn't seal as it should in addition to a hole that has rusted through where the damper handle used to be. The damper, therefore, is letting warm moist are escape into the flue, where it condenses on the walls. To fix both of these contributors to an efflorescence problem, I suggest using a top-down chimney cap. This is a cap easily mounted to the top of a chimney. I recommend the screened variety: the screen helps keep animals and leaves from getting into your chimney, but it also has a spring loader damper to seal your chimney at the top. The damper is actuated by a cable that hangs down the chimney which you latch onto a bracket unobtrusively mounted inside the fireplace. To close the damper you pull the cable snug and slip into the bracket, to open, simply release the cable from the bracket.

Should you need to repair foundation supports due to deterioration associated with moisture, I recommend inserting a plastic membrane to serve as a moisture barrier. This is typically a moisture proof sheet of plastic that sits atop the lowermost foundation support and prevents the ground moisture from soaking into the higher adjoining masonry. For more on foundation moisture control check out the post on moisture proofing your crawlspace.