Foundation question for Dan

Understanding that the building design is informed by the type of materials to be used, what would you say is the most important difference in planning the foundation when using natural materials? What choices do we have in avoiding the use of concrete? Is is possible to plaster over concrete?
Thanks!

I did have to use concrete sometimes because it is the only stuff when there is iron for solidity.
Then we did plaster with natural hydraulic lime,
and there seem to be no more problem than over bricks and lime.
But I am curious to know more...

Hi Valerie...When it comes to foundations other than those made of concrete, I would argue that we don't have many really good choices. There are a lot of options, but really excellent long lasting foundation designs are, in my opinion, few and far between. I think the best option, bar none, is a stone foundation. If you want to avoid using cement mortar, you can dry stack the foundation. That said, stone foundations are hard work and take a lot of stone and a lot of skill. It's a job reserved for the patient and anal among us...or for a professional.

Foundation choice also depends on climate. Earthbag foundations can work fine, but be sure to fill the first two courses with rock and keep moisture away from the foundation walls. These are really great in dry climates. Rammed earth tire foundations are fine, too.

One of the most important things to remember when building a foundation is that you want to prevent moisture from entering the foundation and moving by capillary action into the bottom of your walls, be they dirt or straw bale.

Hi Valerie...

To piggy back on Dan, I will share the following.

Please note that OPC and most concretes in general (not so much natural concretes) are as much amphimictic as they are hydrophilic in nature. This makes them act more like a cotton sweater than a wool sweater...hope that metaphor makes sense to you.

I could not agree more about stone!!!

We build (as has humans for millenia) on stone plinths (often glacial erratics) and then if necessary ston fill between. ALL the ancient structures I have been part of restoring and all the old barns I work on (most well over 150 years in age) have stone foundations that they just "sit on" and have during their lives. Few have little or no displacement after all these decades, just some settling and that often is the result of "modification" to surrounding grade.

I may disagree a little about who can use stone...you do need a mentor, and you do have to be patient, yet the ishiba 石場 styles (or plinth 根石 and cobble stone foundations 玉石基礎) of the Ryukyu Islands 琉球諸島 North to Hokkaido 北海道 is simple, enduring and everlasting. Anyone can master this modality of foundation work as farmers have for thousands of years.

One of the most important things to remember when building a foundation is that you want to prevent moisture from entering the foundation and moving by capillary action into the bottom of your walls, be they dirt or straw bale.

Hugh!!!

DRAINAGE...drainage...drainage...and did I mention....drainage!!!

I would note (teacher in me can't help) that "true capillary action" only happens in cell structure with "capillarity" and in some geologic crystalline structure that form them. The rest is "diffusion" through "cohesion and adhesion." Often now being referred to as "wicking" or "cohesive diffusion." It is the interstitial matrix of the masonry's micro and macro pore structure that facilitates "cohesive diffusion," not "capillarity" as you see it in... say a wooden fence post or in a celery stalk.

Regards,

Dan,
Thank you for your reply.
Xisca,
Thanks for the plastering insight.
Jay,
As a fiber artist, your metaphor makes perfect sense.
I have lots of native stone and would surely like to use it. I have not researched what our zoning office may say about that yet, though...

Hi V,

When I design/build for a client and have to deal with "officials" I get my PE involved...it is all about the "language" you use. I keep this simple and generic. It is a "masonry foundation" that is tectonically stabilized and PE approved...that is usually enough for them to "move on." When it becomes a battle that is when the clout of a professional is needed to quell their worries.

Regards,

j