What are the white crystal-like substances that appear on my retaining wall after it rains?

Asked by Kingkamandi (149

) February 5th, 2010

After it rains these white crystals appear on my retaining wall but only below the part where there is dirt on the other side of the wall. I assume they are caused by water seeping through the concrete as it takes a few days after it has stopped raining for them to appear. Part of the wall is covered (and so it does not get rained on) so i know it is not a surface problem caused by the rain itself. Is this a symptom of a problem I should be worried about?

Here is a picture: <a href=“http://imgur.com/hup28.jpg” title=“Hosted by imgur.com”>http://imgur.com/hup28.jpg</a>

[URL=http://imgur.com/hup28.jpg][IMG]http://imgur.com/hup28.jpg[/IMG][/URL]

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4 Answers

I believe this is lime or some other soluble mineral leaching through. It’s probably nothing to worry about, if that’s the case. If it’s some kind of mildew, then that might be worth getting a treatment or sealant.

JeanPaulSartre (5785

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@JeanPaulSartre is right. This is called efflorescence, and consists of calcium carbonate (chalk), and sodium and potassium salts leached out of the concrete and deposited on the surface by the water passing through. Doesn’t look great, but it’s harmless.

Harp (19179

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Darn, finally a technical question I could have answered correctly, only @Harp beat me to it.

susanc (16144

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Actually you should take measures to seal the block on the side where the dirt is. The constant moisture that the leaching of minerals indicates will eventually cause the brick to deteriorate.

To do this you have to dig the dirt away from the wall and seal the block that is below the dirt line with a waterproof sealant. There are specialty sealants for this or you can use something like cooler or boat sealants.

Merriment (5940

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