Is this efflorescence?

[grantstructure]

Investigating some hollow core planks over a retention pond. There is lots of typical white efflorescence and some large stalagtites in areas. Then there are spots that look like the attached photo. When I broke chunks off it seemed more like spray-on insulation in consistency, but no-one would have ever spray-fireproofed the inside of a stormwater retention pond. I hope.

 

[EngineeringAdam]

That looks like primary efflorescence to me, it can exhibit an insulation type consistency due to salts being brought to the surface during its initial cure.

The stalactites are formed due to the presence of chemicals within the concrete like chlorides.

Primary efflorescence isn't normally a structural concern, but the secondary efflorescence can have a bigger impact on the system depending on the severity.

 

[Ron]

What is showing in the photo looks more like a fungus than efflorescence. Efflorescence is usually crusty and brittle, often friable. It will range in color from white to silvery gray and can be stained by rust. Break off a piece and put in cup of water. If it floats, it's not efflorescence.

 

[PMR06]

It almost looks like mud from birds trying to build a nest, although the swallows around here usually build in the corner where ceiling meets wall?

 

[Lutfi]

At first impression, no.

Regards,
Lutfi

 

[EngineeringAdam]

I didn't know of the check Ron mentioned. Sounds like a good idea.

Others are probably right about it not being efflorescence. After looking at it again it's not transparent enough, efflorescence is friable as Ron said, and because of this it doesn't appear very dense.

 

[grantstructure]

Thanks for the responses. I think the most telling point is that this material did not crumble to powder, the way efflorescence would, but was spongy in consistency.

 

[msquared48]

You are just trying to fool us and the picture is upside down, right?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[charliealphabravo]

It looks a little bit like softening and bubbling of latex paint due to water and perhaps a mild solvent transmission through the concrete. It would help if the dimensional scale was more clear.

But I think it is probably foam/paper/debris that was floating on the water and just adhered to the low spot on the slab as the water level receded.

 

[Ron]

OK Grant....there has been enough speculation here...did you take a sample of the material? If so, slice it and photograph it for us...do the quick test I suggested....let us know the results!

 

[grantstructure]

I'm not sure I'll get back into that retention pond anytime soon, but to try to put this to bed: the scale is somewhat apparent from the texture of the adjacent concrete, with the growth or whatever hanging down about 1.5" at the maximum. These are unpainted hollowcore planks exposed to weather above (and they're not doing very well). Structure is used for parking, so they may have salted it, but this is in Austin, TX, so it shouldn't have been terribly often. The whiteness is either efflorescence or my flash--this surface is unpainted. We have 12" stalagtites in some other areas which are clearly from leaching, but this stuff is different. I did pull a chunk off and it was spongy. My first thought really was spray-on insulation. I chose not to bring it back with me, so I can't see if it will float, but it didn't crumble to powder, which I think is a pretty decent determining test of efflorescence.

Not sure what the source of organics would be for growth, but the geometry of the pond is such that this would never have been directly wetted by the pond filling up (it would overflow before reaching underside of deck.) I'm going to theorize that someone spilled a slurpee on top and this is what happened after the sugars leached through to the underside, until someone can prove otherwise.

 

[Hemifun]

My guess would be mud daubbers or wasps. Definately not effloresence.

 

[Ron]

grant...easy for fungus to growth in the area you described, particularly if you've had leaching and carbonation has reduced the pH of the concrete surface.

 

[tngv752]

Agree with Ron. It is not like normal efflorescence.

 

[MiketheEngineer]

Take a sample to a TESTING LAB. They will tell you EXACTLY what it is...

 

[grantstructure]

Yeah. There are so many other things wrong with this structure that figuring this out exactly is a moot point.

Appreciate the many responses!