Replies

1. 
   jklingel | Dec 22, 2012 01:30pm | #1

   Concrete draws power from car batteries; not any more, if ever. 1,000's of homes have foam under slabs, either with a vapor barrier between them or under the foam; no problem if you address drainage. Compacted gravel under the foam is pretty standard in my area; it acts as a capillary break. Yes, concrete will draw heat from you if it is cooler than your feet; anything will. The more dense the material you stand on, the faster. Fatigue mats help w/ the fatigue. I'd be careful w/ sand under concrete; I've read of some serious issues, so study that one first, as I am not 100% sure.

2. Expert Member
   MALCOLM TAYLOR | Dec 22, 2012 09:11pm | #2

   Portland cement is just one of the ingredients of concrete. It is the concrete you will be standing on, not the portland cement. There is nothing inherent to concrete that depletes energy beyond the density or hardness of the surface. So standing on stone or thick tile would produce the same effect. A slab is a monolithic structure so attempting to make is "softer" or more forgiving by using different materials as a sub-structure won;t work. Your best bet, if you want to use a slab, is to provide a cushioned, finished floor above.

3. GBA Editor
   Martin Holladay | Dec 23, 2012 06:32am | #3

   Kami,
   Many people prefer wood-framed floors over concrete slabs for comfort reasons, although (as Malcolm suggests) you can talk to a flooring contractor about a variety of flooring options that are more resilient and less fatiguing than a bare slab or a tile floor.

   Q. "If a person puts XPS foam underneath the basement slab, it can cause mold because it takes so long for the portland cement to dry out. Is this a possibility?"

   A. Portland cement is always dry. I think you are asking about the length of time it takes the concrete to cure. Concrete will retain its moisture longer -- and will take a little longer to cure -- when placed over rigid foam than when placed over sand. Long curing is not a problem, however, as long as the contractor anticipates it and stays on the job long enough to finish it. Once cured, a concrete slab with rigid foam under it is better in all respects than an uninsulated slab -- and, incidentally, is less likely to support mold than an uninsulated slab.

   Q. "Would putting a foot of small pebbles under the foam be wise and maybe 6" of sand on top of the foam?"

   A. In most areas of the country, a layer of "pebbles" or crushed stone is a routine specification under slabs, and it's a good idea. It acts as a capillary break and helps ensure that your slab stays dry. However, installing a layer of sand between the XPS and the slab is a bad idea. Here's an article that explains why: Concrete Floor Problems.

4. 
   greenhomes | Dec 23, 2012 09:47am | #4

   Thank you Martin, I appreciate the feedback. I think the fatigue is not the hard surface, but the fact that it can drain energy from the body like it can drain from a car battery. It is speculation---but the German factory thing got me thinking. It is not the hardness of the cement, but the properties of the cement that cause the fatigue.
   I will read the article about the sand.
   So to cure the slab, the contractor needs to stay on the job long enough. Does that mean that he needs to work the cement long enough that first day to get it to cure properly because it is going over the foam layer? Sorry if I have more questions, I am just trying to learn something that I have no knowledge about and just want to know. There is a lot of money that goes into building a home. I finally have a beautiful piece of land and I want a healthy home.

5. GBA Editor
   Martin Holladay | Dec 23, 2012 10:13am | #5

   Kami,
   When a car battery is left on damp concrete, it can be electrically discharged to the concrete if the outer case of the battery is damp, or if there is a flaw in the battery's case, because the concrete is a ground. Since people generally don't have positive and negative terminals, nor do people generate 12 volts DC, the analogy doesn't apply to people.

   Don't worry -- concrete won't pull energy out of your body. However, like a tile floor or a granite floor, a concrete slab floor can be tiring if you stand on it or walk on it all day.

   You wrote, "It is not the hardness of the cement, but the properties of the cement that cause the fatigue." A reminder: we're talking about concrete, not cement. And I disagree -- it's the hardness of the concrete that causes the fatigue.

   Concerning the steps required for finishing a newly placed concrete slab: this is a routine part of concrete work. If you will be doing the work yourself, you should apprentice yourself to a concrete contractor, and practice with a power trowel. If you will be hiring a concrete contractor, don't worry -- trust your contractor.

6. 
   greenhomes | Dec 23, 2012 10:46am | #6

   Thank you Martin, I will be hiring the work done.

7. 
   heinblod | Dec 25, 2012 03:00pm | #7

   The OP wrote:

   "HI, I have been reading about Portland Cement and was wondering your thoughts. It had been written that it can cause fatigue from standing on it as it draws out the energy just like it can drain a car battery. ...... "

   Any reference to this 'literature'?

   Having worked with and on concrete in Germany for decades I never heard anything alike. Please publish some references.

   Bags of Portland cement are not designed to be stood on, a safety issue indeed.

   Thank you