It's Not Mold, It's `Efflorescence' - And It's A Telltale Sign Of Water

Q: I have a bunch of white, crystallized, granular-looking mold on my basement floor near my furnace. I'm wondering if this mold is dangerous and what I can do about it.

A: You likely do not have mold on your floor, but rather a phenomenon called efflorescence. Efflorescence is white crystalline deposits that form on the surfaces of masonry products. It is a water-soluble salt. Water carries the salts to the surface of the material through channels and capillary action. When water containing these salts reaches the surface, it evaporates, resulting in visible efflorescence.

Efflorescence is quite common in crawl spaces, in and on chimneys and fireboxes, and anyplace where water has saturated a masonry product. After our recent heavy rains there have been quite a rash of efflorescence sightings. The mere presence of efflorescence indicates you have a water-penetration problem of one kind or other which may or may not get worse in time.

You also may be seeing another type of loosely defined efflorescence - the white powder seen on the surface of gas-furnace flues, in the interior and many times on the floor around a very dirty furnace. This powder results when the exhaust is cooled prematurely enroute to the exterior. The exhaust vapor condenses back to water if cooled too rapidly, leaving the white powder behind (although this powder really is not crystallized). Lower efficiency furnaces with single wall-exhaust ducts are most prone to this, also those in which the exhaust temperature is too low.

Q: I bought an older house recently in Leschi. The deck has a lot of dry rot. Is there a way to stop this from eating my deck completely?

A: Dry rot is really a misnomer. Rot is caused by water, a cellulose product (wood) and oxygen. Wood won't rot on its own. When you hear of someone with "dry rot" in their bathroom or deck or wherever, it is the initial work of water.

To stop rot you obviously need to remove the source of water (difficult on a deck). If the wood is sound, it may benefit from a preservative, staining or painting. Those sections that are unsound need to be cut away like a cancer and replaced. There are wood fillers, bonding agents and hardening putties available (your results with these may vary) that may be appropriate, depending on the extent of damage. When replacing exterior wood, use material that has been factory treated to resist rot.

Q: I do insurance inspections. I can't believe how many people don't have house numbers up, especially in rural areas. I presume the local fire departments are familiar with the neighborhoods, and it is becomes obvious when you get close which house is on fire. However, finding these houses when they aren't on fire is tough. Snohomish and Island Counties seem to be the worst with street addresses not making sense. Thankfully, King County seems to pretty systematically apply the same rules throughout the system.

A: Good point. I'm sure we've all experienced that frustration of trying to find an address with no house numbers in sight. Especially at night. For those who get frustrated by the King County addressing system and seem to think it makes no sense, I offer the following:

All countywide addresses are referenced from First Avenue and Main Street in downtown Seattle. Go north and the designator will say north (with a few exceptions in the close-in city). Go south, east or west in any combination and the designators will reflect those directions and be expressed in blocks from that downtown reference point.

The confusion occurs when the order of the presentation of the designators is applied. When the designator is before the street number it runs east-west. Designator afterward and it goes north-south.

For example: Northeast 85th and 195th Northeast is in Redmond, 85 blocks north and 195 blocks east of the reference point. But 85th Northeast and Northeast 195th is in Bothell, 85 blocks east and 195 blocks north of the reference point.

Named streets are on the same grid and the same rules apply.

Ask The Expert answers readers' questions every Saturday. Send questions to Ask The Expert, Seattle Times, P.O. Box 70, Seattle, WA 98111, or call 206-464-8514 to leave your questions on Ask The Expert's recorded line. E-mail address is dhay@seattletimes.com

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