concrete 'mold' in Mexico

[ebesan]

Why does so much of the concrete work here eventually mold? (I am in the Yucatan)
If that is the right word for this action. The discoloring.
Is there an admixture missing? Something that is used elsewhere? how much is to be blamed on the humidity?
People elsewhere are experimenting w/ new mixtures (i. e. fly ash) to make concrete less wasteful, lighter etc.; in this area, Mexico, is anyone experimenting w/ new formulas?
What is the difference between exposed formwork say, in the US, and here?

Oh, and one more. Could 'rammed earth' construction be done here? What ingredients are necessary? (there is alot of limestone here)

 

[kelowna]

Do you know how the concrete in question was cured?

 

[ebesan]

Here, they mix it right there on the floor; pour it in makeshift forms; walk away.
Never paid enough attention to the 3 ingredients, beside sand, to determine proportions.
For instance, a 2" slab covering my underground cistern, made as per above.
2 years and I see the edges turning black/green.
And all over Mexico, one can see the discolored walls.
Curing is necessary for setting correctly...would that affect other properties?
Why can a wall be poured, (e.g. in the States) the forms removed, and the wall is left as is, w/ no bad effects? curing? other mixtures?

 

[ebesan]

is it efflorescence?

 

[cvg]

qualities of the water and the materials in the concrete including the minerals in the aggregate, cement quality, and fly ash or other additives need to be investigated. You might try taking a sample of the mold to a lab and have it analyzed to see what it is.

 

[hokie66]

Does it wash off? Try using a pressure washer to remove it. If it comes off, it is just dirt, possibly with fungus growing on the dirt.

 

[RHTPE]

ebesan:

I suspect that the tropical climate has a lot to do with the concrete developing a coat of mildew & mold. Given the heat lag of concrete, I would suspect that moisture readily condenses on the surface when its temperature is below the dew point temperature, thus providing a favorable environment for mold & mildew. Try what Hokie66 suggests - if it washes off, then it's probably not directly related to the composition of the concrete mix.


Ralph
Structures Consulting
Northeast USA