Concrete Floor Problem

[Mort Guffman]

My back porch floor has a odd problem. It looks like a chemical reaction. In spots the concrete looks like it is dissolving and turning to a fine powder. I took pictures of it just a few weeks after a thorough cleaning with soap and water.

The porch was painted before I bought the house 2 years ago. The paint is peeling pretty badly. Before it was painted it was covered with indoor/outdoor carpet.

Also there used to be a hot tub out there. I was wondering if chemicals from the spa might have caused this.

I made a web page with the pictures:

I would certainly appreciate any advise

thanks

Mort

[TURTLE]

This is Turtle.

It looks like when they poured the slab the curing was not right or the concrete mix was not good on the slab. I know of nothing that a normal person would use over a slab that would break it down except a jack hammer or a stick of dynomite. It may crack but not just powder up.

I think what people who pour concrete would say as a Bad pour.

TURTLE

[Paul Oman]

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Hi Mort

No your patio isn't dissolving. What you are seeing is mineral salt crystals coming up with water thru the cement. The water evaporates away and the crystals are left behind. There is probably no vapor barrier under your cement.

When the crystals form they can produce 2000 pounds of pressure, thus poping off nearly all coatings.

There are one or two products that will seal the concrete below the surface. They MIGHT reduce or stop the problem. A waterbased epoxy as a next step MIGHT then work as it will soak slightly below the surface and form a very strong bond.

hope this helps

paul oman progressive epoxy polymers

[Ed Clarke]

This looks like efflorescence. Water is coming up through the concrete and carrying soluble salts with it. The water evaporates and leaves the foamy looking powder. There are cleaners that will remove it, but you really need to get rid of the water problem before the concrete is destroyed.

[Mort Guffman]

Thanks everyone for the good advice. The yard back by the porch is always wet/damp so there is definitly a moisture problem. The plants like it...

mort