Cement, Moisture and forces of Equilibrium- Wenatchee and Leavenworth Home Inspection

On a recent home inspection my client asked me to look at a part of the foundation that he thought may be failing.

After evaluating the issue it was obvious the problem was not from failure of the foundation but the failure of not properly installing a proper vapor barrier for the concrete.

Most people think concrete is water tight. We make water tanks and dams out of concrete, right. Concrete can do a good job of containing liquid water (at least when there are no cracks). But water vapor moves readily through concrete. The rate of moisture transfer depends on the concrete's porosity and permeability.

Think about the concrete slab in your home as a hole in the moist ground. The soil below the concrete will almost always be damp. It nearly always has a relative humidity of 100%. That means it is a continuous source of moisture into the slab.

All natural systems always tend to migrate towards a state of equilibrium. This is much like a hot cup of coffee transfers heat to the air in the room until they are both at the same temperature (the second law of thermodynamics).

In chemistry higher concentrations of a chemical will move towards areas of lower concentration. The same is true for areas of higher or lower relative humidity (Relative Humidity is actually a measure of the vapor pressure of water vapor in air). This movement of this moisture vapor is called diffusion.

These principles mean that if the moisture in and below the concrete slab are higher than the relative humidity of the air above the slab the moisture is going to try to move into and out of the slab. Without a vapor barrier, the relative humidity in the slab or just below is most likely will be 100%. Since the air is seldom that humid, moisture is going to move from the slab into the air and as the surface dries a bit it will draw moisture up from the bottom (capillary action).

Rust and cracking from moisture diffusion    Moisture through a receptacle

Here we see metals in direct contact with the concrete that has a high rate of moisture diffusion. It is causing the metal to rust and expand thus cracking the concrete. This is the problem my client was seeing.

The attention to the detail of the vapor barrier prior to the concrete being poured is critical. Understanding the principles behind moisture diffusion will help you understand why this be happening in your home.

Cement, Moisture and forces of Equilibrium- Wenatchee and Leavenworth Home Inspection

NCW Home Inspections, LLC  is located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Orville, Cle Elum, East Wenatchee, Quincy and many more...                             

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12 Comments on Cement, Moisture and forces of Equilibrium- Wenatchee and Leavenworth Home Inspection

JUN
26
2011
1,242,529 Points 158 Featured Posts Outside Blog Called Shot Master

Good morning, Donald. Inspected a real POS with similar issues yesterday. I have to quit for awhile. It is giving me a headache...
11:55am • #1
293,173 Points 66 Featured Posts Outside Blog Called Shot Master

Michael,

The worst part about these type issues is that the fix is not an easy one to do it right.
11:58am • #2
917,068 Points 178 Featured Posts Outside Blog Attended Rain Camp Called Shot Master

Don, for this reason it has always surprised me that vapor barrriers are not required under footings----could prevent a lot of wicking of water into the concrete wall.
2:04pm • #3
1,150,590 Points 53 Featured Posts Outside Blog

Don,

I hope while you were there you re-charged all your batteries by plugging into that nice receptacle. Had to be tempting to you.
2:05pm • #4
155,778 Points 13 Featured Posts Outside Blog Called Shot Master

That's a basement wall your showing the rusted electrical boxes in, so this is water coming in through the wall not so much from below or through the slab in your example.

To answer Charlie, footings have to be on undisturbed soil. Placing a vapour barrier and maintaining that 'undisturbed condition' is difficult to achieve.

When vertical migration of water is a problem the vapour barrier can be placed on the footing so it ends up between the footing and the foundation wall. 
5:20pm • #5
293,173 Points 66 Featured Posts Outside Blog Called Shot Master

Charlie,

A vapor barrier and they should have to seal the form ties also. I see so much water protrution through them.

Steve,

Yeah that electrical outlet was a nice one.

Robert,

There was water/vapor diffusion on the bottom slab and through the walls. This actually was a bunker of types, so very similar to a basement. I did not show a picture of when I moved some materials that there was a large amount of condensate on the bottom of the materials. But the principle still holds true whether its on the vertical or horizontal plane.
6:03pm • #6
JUN
27
2011
537,918 Points 6 Featured Posts Outside Blog Called Shot Master

Good evening Robert, great photos and your input on the use of moisture barriers is appericated. 
12:30am • #7
293,173 Points 66 Featured Posts Outside Blog Called Shot Master

Dan,

It really is amazing how moisture works and how it can effect homes.
1:10am • #8
567,910 Points 140 Featured Posts Outside Blog Called Shot Master

Good physics lesson. They don't seal form ties out there? Here in CT, where the large majority of homes have basements, they are sealed. If not they will usually leak.
7:40am • #9
293,173 Points 66 Featured Posts Outside Blog Called Shot Master

Jim,

They seem to never seal the form ties in crawlspaces. Most of the time you will find them rusted out and weeping. In basements they are but I was thinking of crawlspaces.
8:32am • #10
JUN
28
2011
155,778 Points 13 Featured Posts Outside Blog Called Shot Master

Here a crawlspace automatically dates the home to pre-ready mix times. 98% of the time new construction it is basements unless you're on a rock outcrop or are a boat trailer length from water.
5:30pm • #11
JUN
29
2011
293,173 Points 66 Featured Posts Outside Blog Called Shot Master

Robert,

I would think so with where your frost line will be. Here in many areas it is 18 inches.
10:15pm • #12


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