Cold weather leaching on bricks

We’ve had a few cold snaps here lately. After each one, I’ve noticed that the new brick work on our downtown sidewalks has a white, powdery stain on it. It appears to be leaching out of the brick and it’s gone after a rainstorm. What is this substance and why does the cold weather cause it to appear on the bricks? This is south FLA and we don’t put salt on our surfaces.

Vocab word of the day: efflorescence.

Water makes its way throught the brick and brings some salts contained within to the surface. When the water evaporates away, the salt is left behind.

It certainly appears to be a type of efflorescence, but the article does not say what effect, if any, cold weather has on the phenomenon.

Heh, and here I though we were the only ones with this. It’s been happening recently to my antique pavers on the porch but I figured it was just because they were old and porous. Yes, it did appear twice right after two unusually cold events and yes again, I tasted it and it is indeed salty.

Yet again, no matter how unusual something is that you encounter, some doper(s) will know exactly what it is.

What’s salt doing in the bricks?

My only guess there is that cold air tends to be drier air.

Bricks are made from clay, which is a form of dirt. Dirt contains salt. (That’s why the ocean is full of salt water.)

Warmer air is usually more moist air, and the water in the air acts on the water soluble salts.

Cold weather comes with dry air. The delicate salts left on the surface, which will dissolve with decent amount of moisture in the air, get to hang around in the drier air.

It’s not the cold air, per se, bu the cold air is a clear indicator that moisture levels in the air are lower than usual.

So, the salts are always showing up, but are constantly dissolved by water in the warmer/moister air. Remove that warmer/moister air, and the salts get to remain solid for a while (thus, white and sort of powdery).

(Warmer/moister is a relevant term. The air could be warm/moist enough to dissolve the salts (ergo, moist to the salts), but not be so warm/moist that a FLA resident would call it such).