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Author Topic: Soil pH near house foundation  (Read 497 times)

Draak

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Soil pH near house foundation
« on: December 16, 2019, 12:10:02 AM »
This topic could potentially go on the temperate or tropical fruit boards. However, since many people on this forum push their zone by planting close to their house, I thought it would be particularly appropriate here :).

There is a wisdom and concern that has been passed down through the community that soil near cement, such as by sidewalks and the house foundation, will be more alkaline than soil further away. This is because cement is a very alkaline material (pH > 12), and any material that either mixed with or leeches into the surrounding soil may raise the pH of that soil. However, determining how much the pH raises is an unintuitive venture into the world of chemistry. If the soil has no pH buffering capability, then the soil pH will immediately rise to near the pH of cement with the addition of only a tiny amount of cement, let alone an entire sidewalk or foundation. If the soil can pH buffer, then the pH will change, but only slightly.

Since soil is not at all a simple thing, it is best to do an experiment. There is fortunately a free thesis available from the university of Florida where a person had done a good experiment on this topic in Gainesville, Florida: https://ufdcimages.uflib.ufl.edu/AA/00/01/42/66/00001/influenceofconst00rich.pdf . In chapter 2, he was investigating the effect of pH on termite pesticide. Since this pesticide is sprayed closed to the house, determining the effect of pH on soil around the house is particularly relevant. On table 2-2, you can see how he started with pH 5.5 soil, and created various mixtures of soil/cement, from 33% cement to 90% cement. On the day of the mixture, the pH rose to 6 for low fractional cement mixtures, and to 9 for high fractional cement mixtures. However, after 10months, all mixtures either rose or dropped to pH 6.5~6.9. Quite strange! However, this shows that a homeostasis mixture all tends toward a neutral or slightly acid mixture after time.

In table 2-1, he looked outside the laboratory environment to houses around the neighborhood, and sampled soil within 4" of the foundation from various houses. New construction showed pH levels that are approximately on par with a low fractional cement mixture for wood sided or stucco houses. Houses with a brick veneer exterior had very high soil pH (one house had a pH of 10!). Overall, he found quite a wide range of pH for both new and old construction, regardless of what exterior the house had. Some houses were able to maintain an acid pH near the foundation that matches the original soil, while other houses had a pH >8 even after 10 years.

The real world results were strikingly different from his laboratory results. Even a mixture that is only 10% dirt went to a neutral pH in less than a year, so why weren't these houses exhibiting the same trend? My hypothesis is that he did not have a homeostasis condition in the real world. When water interacts with the house foundation, minerals will effloresce out of the cement and into the surrounding soil. This continually introduced alkaline material that rose the pH of the soil. Depending upon which house he is sampling, which face of the house he is sampling from, how wet that face gets, etc... he could see a large variation in his results.

Regardless of why this pH increase is occurring, the answer to 'will the soil next to be house be alkaline' is 'maybe.' There were a few samples he measured that had no apparent pH increase at all. If efflorescence is a major factor in the pH, then the answer may depend upon whether you have gutters installed, how well you shed water away from your house, and which face of your house gets the most rain. If you live in an area with little rain, like California or Arizona, then this may be even less of a problem.

If you need an answer better than that, you'll have to buy a *good* pH meter and test your soil yourself :).

Oolie

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Re: Soil pH near house foundation
« Reply #1 on: December 16, 2019, 01:34:28 AM »
I didn't see solubility mentioned anywhere. If you're going to talk about pH increases, you must consider the solubility of the cement.

Try to get set cement to dissolve in water and you will see the problem, which is that it doesn't dissolve in any appreciable amount.

Therefore it's not going to produce significant amounts of Hydroxide ions to raise the pH.

That's before you get to the topic of buffering capacity of the soil which would limit the pH change further.


Draak

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Re: Soil pH near house foundation
« Reply #2 on: December 16, 2019, 02:34:40 AM »
I didn't see solubility mentioned anywhere. If you're going to talk about pH increases, you must consider the solubility of the cement.

Try to get set cement to dissolve in water and you will see the problem, which is that it doesn't dissolve in any appreciable amount.

Therefore it's not going to produce significant amounts of Hydroxide ions to raise the pH.

That's before you get to the topic of buffering capacity of the soil which would limit the pH change further.



https://en.wikipedia.org/wiki/Efflorescence

Oolie

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Re: Soil pH near house foundation
« Reply #3 on: December 16, 2019, 03:29:21 AM »
I didn't see solubility mentioned anywhere. If you're going to talk about pH increases, you must consider the solubility of the cement.

Try to get set cement to dissolve in water and you will see the problem, which is that it doesn't dissolve in any appreciable amount.

Therefore it's not going to produce significant amounts of Hydroxide ions to raise the pH.

That's before you get to the topic of buffering capacity of the soil which would limit the pH change further.



https://en.wikipedia.org/wiki/Efflorescence

Is the rain in your area saltwater?

Triloba Tracker

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Re: Soil pH near house foundation
« Reply #4 on: December 16, 2019, 01:58:51 PM »
I have also wondered about pH affect of concrete.

I have some trellis posts set in concrete and plants very close to the posts. Unfortunately i have to replace a couple rotten posts, so this has been on my mind.
But i can't think of any way around setting them in concrete.

Daintree

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Re: Soil pH near house foundation
« Reply #5 on: December 16, 2019, 02:08:18 PM »
I made a beautiful fountain for my greenhouse, with several little pools, out of cement, and discovered that it really raised the pH of my pond that I use as a water source for my plants.  Took four of us to lift it into the truck to haul it to the dump!

Carolyn

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Re: Soil pH near house foundation
« Reply #6 on: December 26, 2019, 07:44:55 PM »
My trout pond its build from thick concrete and the water has 12 ph after more than 10 years.
I stopped using that water to water trees except almonds wich can handle high ph verry well.
The ammount of buffer thats in that water after sitting a year in the concrete basin its high.
But on the river bed near my house there are big cement( concrete) dams wich have low ph ,as low as 5 because they get washed away by rain water and there is acid loving flora and sphagnum moss growing on those concrete plates.
You can try to seal the concrete with liquid glass,sodium silicate and that should stop the leeching.
Its also an amazing substance that turns into real glass and cheap to buy if you can find it.

 

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