Mystery White Substance on Garage Floor
February 26, 2018 5:08 PM   Subscribe

A couple weeks ago I noticed a fluffy white substance on certain areas of my garage floor. It looks a lot like snow, but it isn't. Temperatures have been well above freezing here recently, and it doesn't melt if you touch it. Pictures and a lot more detail inside. Does anyone have any idea what this could be?

I suspect it may have been there for longer, but I first noticed the substance a couple weeks ago when temperatures here rose well above freezing. Prior to that, if I had seen it, I think I would have assumed it was snow and paid it no mind.

The substance is mostly concentrated near the path of the car tires and near where the snowblower and trash container sit, which suggests it could be something which came in on them. There is also an accumulation of powder near one side of the garage door, where nothing in particular normally sits:

Picture 1
Picture 2

If I touch the substance, it moves easily (does not stick to the concrete at all). When rubbing it between my fingers, the substance feels soft, dry and powdery. It does not feel grainy, coarse, or abrasive at all. I poured a small amount of water on some of the substance to see what would happen, and it immediately and completely dissolved when touched by the water.

I have only lived here since July, so I don't know whether this has happened here before.

I was wondering if this could be some kind of residue from road salt, but the snowblower and trash can wouldn't really have much exposure to that, unlike the car. I have used a small amount (less than 5 lbs over the entire winter) of SafeStep 4300 on the sidewalk and driveway; the listed ingredients of that being sodium chloride, magnesium chloride hexahydrate, and an unnamed corrosion inhibitor. I've never known road or driveway salt to form a fluffy powdery residue like this, and I have been reluctant to taste the substance to see whether it tastes salty.

If any of you have any idea what this could be, or ideas for me to try to help identify it, I'll be glad to hear them.
posted by Juffo-Wup to Home & Garden (5 answers total)
Most likely salt. It's dissolved on your car, wets the concrete and as water evaporates, forms crystals again.
posted by Yavsy at 5:10 PM on February 26, 2018 [7 favorites]

possibly efflorescence caused by the moist conditions. It's basically salt but it's coming out of the concrete via the extra moisture on the floor which then evaporates leaving the crystals behind.
posted by GuyZero at 5:12 PM on February 26, 2018 [11 favorites]

Picture 1 looks very similar to the photos in this article on efflorescence. It could also be just plain old re-crystalized road salt coming out of melted snow.
posted by GuyZero at 5:13 PM on February 26, 2018

Efflorescence, imo as well. The deposition pattern is pretty characteristic.
posted by bonehead at 5:23 PM on February 26, 2018

I guess I should have Google Image Search'd harder; someone suggested efflorescence last weekend, but the first page or so of images that came up looked nothing like what I've got, very much unlike the image in GuyZero's article.

Thanks, everyone!
posted by Juffo-Wup at 5:32 PM on February 26, 2018

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