My house is about 20 yrs old. The concrete in spots has like a white fuzz on it and where this fuzz is it looks like some one poured acid. The concrete is being eating away. What is happening. It is on the drive way and back patio and now I think on the slab. Can any one tell me what the heck is going on? Thanks!

It's effervescence. It's removed by a powder and water made by Drylok or muratic acid which is dilute hydrochloric acid. Both are available at hardware stores. It's caused by the leaching of the salts of the concrete. You need to find the source of the moisture and/or find a method to seal the concrete after etching.

I put this from PM back in the forum where it belomgs.

Thanks for your response.
So, it is caused by moisture?? I find this on my drive way, on my patio in my garage AND now I am afraid it is on the main house slab. I am getting some moisture issues in one of my bed rooms. What would your recommend? How do I find this moisture source? Can you please let me know. Thanks again.

Barry:
We get notified of responses via email, so your response really belongs in the forum.

I really don't know how you might find the source, but some possibilities are:

1) Broken water pipe
2) A spring on your property

The main house slab and bedroom you might be able to arrest by using a dehumidifier, but it might get expensive to operate.

You might have to install a sump pump.

You may have to emply a professional contractor that might be able to use Ground penetrating radar" to locate the source. See Ground-penetrating radar - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Ground_penetrating_radar)

To remove it, your going to have to etch. To stop it, you'll have to either remove the source of the moisture, remove the moisture or create a waterproof barrier.

For instance, Drylock paint is good for cinderblock walls of a basement.

Waterproofing a basement from the outside wall and/or installing a real french drain on the inside is another way.

I do think the fix is beyond a do it yourselfer.

The moisture is likely coming from the opposite surface and slowly leaching through the concrete because of the intense pressures. As an example, Helium leaks out of everything because it's the smallest molecule. See low long it takes a balloon to deflate. Mylar balloons slow the deflation more than a simple rubber balloon.

Again via PM from Barry D:

Well, I live out in the desert not much moisture out here period. However, when it rains it rains hard. My water bill is pretty low so I don't think I have a leak in the pipes under the slab. Anyway, most/all of the water lines are run through the attic. Only pipes under the slab are the sewage. What I think is happening in terms of the bedroom issue is that water, when it rains, puddles in the front yard 8-10 feet out from this bd room. I think the water / moisture gets sucked up by the dry soil under and around this bedroom and is coming up in the bedroom. The whole room is tile. I have noticed moisture in some of the grout joints and seen rust under the closet door trac. As far as the back yard I have a planter box right by the area on the patio so may be it is seping under the patio slab and this white crap is coming up. And as far as the drive way the sprinkler system is always hitting this area with water. So, may be I have answered my own question. The key was moisture. So, my friend thanks for all your help I really do appreciate it. Take care