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.

How To Fix a Damp Crawlspace and Prevent Mold

The purpose of foundation vents is to allow passing air to carry moisture out of crawlspaces. Except in especially dry climates, this often isn't enough. Even in warm hot summer months the humid moisture laden air will condense on the cooler foundation walls, pipes, ductwork, and even the underside of the flooring. Moisture, still air, and relative darkness is the perfect breeding ground for mold and mildew.

One mold inspector/technician I know recommends leaving the vent's open year long (trim hedges or other obstructions back to allow better air flow) and also wiring the crawlspace with low wattage lighting to run 24/7.

These tips will help keep your crawlspace dry and mold free:

1. Create Better Drainage around your home to prevent rainwater from seeping under the foundation. Grade soil to about .5 inch per foot. Import the soil if necessary, if you'll pardon the pun, it's dirt cheap. This step is highly recommended even if you have gutters to direct the rain water coming off your roof. If you do have gutters, make sure the water is directed away from the downspouts and not pooling back to the foundation.

2. Insulate the Exposed Foundation walls with 1.5 inch rigid, moisture-proof insulation such as Thermax, taping the seams. It would also be a good idea to use this same insulation to insulate the rim joists (the joists that sit atop the foundation walls) and caulk to prevent air flow.

3. Cover the Dirt Floor of the crawlspace with a heavy plastic (10-20 mil) moisture barrier. You want the barrier to be mostly continuous (a few accidental holes wont undo the protection and may even help puddles from heavy rains or a busted pipe drain off) so overlap and tape the seams. Attach the plastic at least 6 inches up on the foundation walls.

4. Cap the Interior of the Foundation Wall with a strip of the plastic sheeting and galvanized flashing to complete the moisture barrier. The flashing will also serve as an obstacle to termites (not a complete defense, just a part of your control program.

Better moisture control not only helps prevent mold and mildew growth, but also will help to extend the life of your ductwork, plumbing, pressure tanks, and hot water heaters located in the crawlspace.