Nope! This is not an icicle. It’s too warm outside, the grass is growing.
This is overhead at the top floor rear balcony of a 4 floor condo building that is less than 10 years old. The edge we are seeing is the concrete roof slab which extends out to cover the building-wide balcony areas.
So it’s not an icicle. So what is it? Well even though this is not the roof of a limestone cave, it is in fact a stalactite.
Yes a mineral deposit from chemicals leached out of the concrete roof deck. The chemistry here is closely related to that of the limestone caves although slightly different.
That variation is not so important as what it tells us about the building, it’s roof slab and the roofing membrane. This one is large for a concrete stalactite and indicates a rapid build up which means a concentration of water seepage flow here or a lot of that water flow.
Look at the pale whitish area leading to that ‘icicle’. It has a little ridge of the same deposits along its length and darker ‘wet’ staining on a wide surface on either side. This is sign of a linear crack in the concrete through which this water is seeping.
Without having seen the roof membrane materials we already know that water proofing membrane has been compromised. I didn’t have access to this roof but I have learned what I needed to by understanding what I did see.
Now what if a resident had taken a broom and smashed off this “icicle” stalactite? I may not have recognized it so readily. You can be sure that any overhead cracks in concrete are going to be closely examined for this type of mineral deposit.
The old geologists mnemonic; “Mites (stalagmites) go up and tites (stalactites) go down.”
Original blog post on ActiveRain: Link to Blog Post