Flagstone for cob foundation?

Is flagstone suitable for a cob foundation? I'm worried it will be too weak, considering California is prone to earthquakes.

Conner Choi wrote:Is flagstone suitable for a cob foundation? I'm worried it will be too weak, considering California is prone to earthquakes.

Our outdoor cob mix used a 10:1 mixture of adobe cob mix to portland cement. This could be an effective filler, but for the outside coat (3/4" to 1"), it would be better to use a cement-only mixture, similar to tuckpointing. I would think, that if you want to stand up to earthquakes though, you'd be better off with rebar and concrete. Aren't there building codes in this area?

I was planning on using them for foundation stones. Do you have any input in that department?

Sure, you just need good drainage, and natural stone foundations need long skinny stone, and need to be extra wide. Technically i guess flag stone for a "foundation" is a no. But a trench with a flagstone stem wall, sure. Don't take my word for it.

Conner Choi wrote:I was planning on using them for foundation stones. Do you have any input in that department?

Maybe I misunderstand. I thought you wanted to use flagstone for the foundation. I wouldn't use Cobb for a foundation. Rodents can burrow right through. Even with a French drain, you'll undoubtedly have moisture penetration.

Hi Conner, et al,

I am not sure if you have read any of my other posts, but I am a traditional builder and stone is part of that system very often. I am also a "Historic Preservation Artisan," and have many different discussions and consultations on my (and many other forums) on LinkedIn should you care to find me there. These are "academic," and more aimed at professional builders/restorationist/architects...but there is still a great deal that could be learn, if interested.

Without seeing your stone type I could not say for 100% but for the harder flag stone types, they can work very well for "single story" structures. Anything over that and I would want to see load testing done, and/or be following a vernacular pattern for a region.

I don't mean to counter other sources you may read or find, but OPC (ordinary portland cements) are highly unadvisable...in any concentration...when working with traditional or natural building modalities. The use of OPC has seeped into the "natural building circles" from many different sources and is becoming all to common "bad practice" in some areas. This is a really big problem in the U.K. and other restoration venue, and without getting into all the "technical and historical" issues with it...I just would say that OPC is not compatible in its ability to interact with natural materials. isn't permeable like clay and limes, and the industries that produce it are some of the biggest polluters we have on this planet. Those reasons alone are good enough for avoided OPC whenever possible. If a "cobb mortar" is deemed unsuitable for some reason, then a Lime cobb or just lime mortar can be employed. Traditionally many foundations (some well over 2000 years old) are a form of "dry lay," with cobb mortar. In a fashion the stones are fitted very tightly. As the mason determines a good fit, then a "buttering" of "cobb" is placed on the stones bedding area before placement. After the wall is starting to dry and set...the "joints" are "raked." Later, a more durable and weather resistant lime mortar can be "pointed" into the joints.

If this foundation is in a tectonically active region than I would highly recommend not using one of the "ashlar" lay patterns for the stone...but instead a stronger "herringbone" pattern with lime mortar if possible (or very well fitted stone with cobb mortar.) Herringbone patterns are found throughout regions of the world with major seismic events like Turkey, across Asian and of course into Japan where this method dominates.

If the "rock work" is "rough" and you do plan on "rendering" the wall (aka parging or plaster) then again do not use modern OPC (or OPC base materials) but a proper lime render. Within the trades..."renders" are exterior plastering and the term "plastering" or "plaster" is indicative of "interior work."

I won't (really can't) go into great length on the proper methods for actually laying stone as that is best "learned in person" as one could write (and have written) many books on the subject. I can answer questions if you have any....

Regards,

j

Jay C. White Cloud wrote:Hi Jim,

I am not sure if you have read any of my other posts, but I am a traditional builder and stone is part of that system very often. I am also a "Historic Preservation Artisan," and have many different discussions and consultations on my (and many other forums) on LinkedIn should you care to find me there. These are "academic," and more aimed at professional builders/restorationist/architects...but there is still a great deal that could be learn, if interested.
j

Jay,
Yes, I have read some of your posts, and you seem very informed - a subject matter expert. I wish I could have consulted your forum expertise 30+ years ago, when I owned a house that was built in 1867. The house had a massive stone foundation, with a 3-wide brick, 2 story structure above. The stone foundation was in good shape, but the brick, with the lime/sand mortar used in the 1800's, needed tuckpointing. After replacing the original roof, along with the 4 layers of asphalt shingles, and doing a number of other jobs; being low on money, I spot-tuckpointed the bad areas. I see your point about stone and concrete. I never thought of that before. Brick, being more porous probably works better with concrete. Thanks for the info. Keep up the good work!

Hi Jim,

First...let me apologize...I was way too tired to actually post, but felt I should...

The post should have read "Conner, et al," so I didn't mean to "single you out," My mistake.

I spot-tuckpointed the bad areas. I see your point about stone and concrete. I never thought of that before. Brick, being more porous probably works better with concrete. Thanks for the info. Keep up the good work!

That sounded like a fine brick form of Victorian architecture...still many left, but unfortunately so many are being destroyed from "improper maintenance" and "repare methods" (not restoration.) However, more so than stone...bricks can't stand being "restricted" and need to expand and contract with seasonal and chronological changes...Concrete (modern OPC especially compared to vintage "natural cements") do not nor ever will allow this as they are not "sympathetic materials" by nature to something like brick, and is not a compatible constituent...Some stones "can take the pressure" but even then I would only use a "natural cement" and that would be in a "like for like" scenario of a restoration only in most application...OPC cement-only mixtures will often fail or cause damage in these applications. Rebar too, is not recommended in concretes as it has been applied in the past due to spalling issues for "rust jacking" and other interstitial challenges within modern OPC concretes. Code is a "minimum standard" and even this is flawed in many ways...

Many of the old brick homes are being inundated with plastic paints, house wraps, foams, concretes, and all manner of modernity.

One very expensive "horror story" I saw about 20 years about in the Chicago area was one "jacked up" to have its very beautiful and in excellent shape...all stone foundation...removed!!! The "Architect of hire," that was allegedly a "Historic Restoration Expert," claimed that the stone was not stable enough or as strong as concrete for restoring the home. Neither of these points of information are accurate, nor did he disclose that his brother in law owned a failing concrete company that "won the bid" to tear out the old stone foundation...

The owner had hired this architectural firm to "remodel and historically restore" the structure. I (et al) was called in by the owner to consult on this "after the fact." Nothing this Architect did, nor the contractors he "insisted on" had any ethos in historical work. To make maters worse he "tuck-pointed" all the joints also with "concrete mortars." The bricks crack, exploded and spall during the first winter and spring to the point that the structure was finally condemned by a PE firm my colleagues recommended. A very large lawsuit and court case (which I like to stay out of!)

Bottom line...in accordance with the "Burra Charter" and other Historical and Artifact conventions, preservation, restoration and reconstruction standards and guidelines of "good practice."...The baseline ethos is:

"Like for like, in means, methods and materials..."

For me in the "natural building arena," (which I think of mainly as just more "traditional building") I follow the same understanding...Modern materials just don't "play nice" with old or natural materials in most applications...Especially OPC's which are just nasty stuff all around...

Regards,

j

Jay C. White Cloud wrote:
That sounded like a fine brick form of Victorian architecture...still many left, but unfortunately so many are being destroyed for "improper maintenance" and "repare methods" (not restoration.) However, more so than stone...bricks can't stand being "restricted" and need to expand and contract with seasonal and chronological changes...Concrete does not nor ever will allow this as they are not "sympathetic materials" by nature, and is not a compatible constituent...as cement-only mixtures will often fail or cause damage in these applications. Rebar too, is not recommended in concretes as it has been applied in the past due to spalling issues for "rust jacking" and other interstitial challenges within modern OPC concretes. Code is a "minimum standard" and even this is flawed in many ways...
j

Actually it was an old farmhouse, that at one time comprised quite a plot of land in South St. Louis. Today that land would be worth tens of millions of dollars. We rehabbed most of it, but had to sell, just prior to finishing. It is now the most majestic house in that neighborhood. There was an original wooden plaque that dedicated the opening of the house, written in old German. It was the biblical quote, "As for me and my house, we will serve the Lord", with erection date of 1865, and opening date of 1867. We left the sign with the house.

I'm not so down on concrete as you are. On the above house, I worked with my cousin, a professional mason, rebuilding our chimneys. In lieu of ready mixes, he preferred to mix his own concrete, using lime, sand and cement. The bricks were original, reused from the house. He was able to simply pull the bricks off, with little or no chiseling, from the original lime/sand mixture. Granted, this was 120+ years later. We had no problems for the next four years, while living there.

We did use a lot of concrete in our tire-bale bermed-earth home. I knew the environmental issues associated with concrete, going into the project. But the resulting home, is net positive-energy, and that's what I wanted. In this case, I feel, the end justifies the means. I'm not sure if you saw my thread on our tire-bale home, but here's a link.

https://permies.com/t/48037/earthship/Pseudo-Earthship-Tires

All this said, I have a real respect for those who use the older building techniques. i have a friend who does stone work with no mortar at all. I have another who built a home without any nails. Another one wouldn't use a pneumatic nail gun.

Hey Jim,

I did see your post on the Earthship you GC'd...and I know Mike, as anyone in this field has too if they been around it for very long. I will post there today so as not to detract from this post topic...

I'm not so down on concrete as you are...

I'm not really "down on concrete" as much as "well jaded" after 30 plus years (and I still have to use in on too many jobs) has taught me just how lacking it is as a material and the horrendous environmental issues with it and the industry behind it. It doesn't last as long as the industry states it will, which is clearly reflected in our failing infrastructure and modern buildings to even come close to what the Egyptians and Romans did with cements 2000 plus years ago. I actually love "natural cements" and the "relearning" that is being done in the area of geopolymers. Nevertheless, modern OPC is a ghastly material that I see way more fails in it than success...especially over time...It is too over used, misapplied and still grossly misunderstood...even by many experts. One of the most insidious elements I find about it is its ability to "hide issues." From rot and decay to built up interstitial moisture damage within the wall or mass matrix of a structural diaphragm or building member...these issues can stay well hidden for years to decades. It is not until a tectonic event, remodeling or other catastrophic fail do we understand just what the "concrete" was hiding and/or contributing to...We just had another section of a parking garage fail, and I have a contractor/colleague now that is dealing with an old (>30 years) gunited retaining wall failing...I just see it all over the place, and it is avoidable if we can change the industry and our collective approach modalities to how we use "lime" and build with it...

I worked with my cousin, a professional mason, rebuilding our chimneys. In lieu of ready mixes, he preferred to mix his own concrete, using lime, sand and cement. The bricks were original, reused from the house. He was able to simply pull the bricks off, with little or no chiseling, from the original lime/sand mixture. Granted, this was 120+ years later. We had no problems for the next four years, while living there.

This is very common and I see "professional" modern masons do it all the time...

It is not "restoration work" and it is...unfortunately...surreptitiously odious for these old buildings. Like so many things related to modern formulations of OPC concretes the issues do not reveal themselves for years if not decades. As you noted above the old lime mortar came out very easily. That is what it was and is suppose to do! It is a sympathetic and capable material to brick, as it is also a permeable (breathable) material...The concrete enhance blend that was used to repoint the farm house with is not a properly permeable material and is entirely too hard a medium for old brick and even modern more vitrified bricks do not always suffer well these 'cement blends. The damage these blends cause may very well take decades if not a century or more to start causing the damage it inflicts...often in the interstitial zones out of view. Just trying to remove these modern mortars is virtually impossible without irrevocable damage to the historic fabric it is made part of. The use of these modern blends, outside the proper modalities and good practices in "historic restoration," has become a mainstay of many of our businesses within the Historic Preservation Field. Good for business...but most of us would rather not see it happen in the first place as it is very disheartening to see the damage we can do little about after its improper application.

Regards,

j

I certainly see your point, and there is a lot of evidence, as you say. A case in point in my city of birth, St. Louis, is the recently demolished Busch stadium. Built in the '60s, with massive amounts of reinforced concrete, it was probably expected to stand for hundreds of years. I heard that the maintenance was just too costly, and that there were a lot of structural issues. Contrast this with a structure like the Roman Pantheon, which amazed me, when I visited, and is over 2000 years old.

Maybe I'll try to build my next tire bale house without concrete. Let's see, adobe covering for the bales. Ceramic tile floor. Not sure what to do about the bond beam though...

Jay C. White Cloud wrote:

If this foundation is in a tectonically active region than I would highly recommend not using one of the "ashlar" lay patterns for the stone...but instead a stronger "herringbone" pattern with lime mortar if possible (or very well fitted stone with cobb mortar.) Herringbone patterns are found throughout regions of the world with major seismic events like Turkey, across Asian and of course into Japan where this method dominates.


j

Hi Jay,

Could you give me a description of how to lay a herringbone pattern? I looked up some pictures on the internet, but I'm not sure exactly how that ties into a foundation.

Thanks again,

Conner

Hey Conner,

Stone work is one of those subjects that can't really be "gotten into" with much detail of "guidance" unless a person already has a real healthing background and experience laying stone...especially "real stone work" and not modern "glue it on with cement" stuff. Stone is as challenging in many ways as timber framing.

I can say that for herringbone, vertical work, slant work, oblique work, knitted walls, and related "non-ashlar" stone work...all the same "rules" apply as they do for any "good practice" in dry laid stone work. I reference dry laid, because "real stone work" is always approached as if there is "no mortar." Too many DIYers and even many "professional" (!!??) masons think of mortar as being part of what holds a stone wall together...

IT ISN'T!!!NOT EVEN A LITTLE BIT!!

Sorry for the "emphasis" but this is probably the biggest and most common mistake (beside too many head joints and not enough bridging/tie stones) that i see in stone work....

As example of "how bad it is," in just looking up stuff to share with you about "stone work" I would have to say conservatively 70% of it is not only "bad advice" it is down right "WRONG." The link below was my "first hit" and from materials to technique photos...it is simply hideous...This is why I have become such a nag about folks "vetting information" really well on all manner of things related to "natural" (aka traditional building methods.)

Very bad stone work and advice...just an example what not to do or follow!!!

One of the first things to suggest is going to the "root language" and culture that has created some of the most enduring forms. The Chinese and Korean terms for these dry stone wall methods escape me at the moment but the Japanese have some of the finest apex forms of Ishigaki 石垣 (stone wall) that are in the Ajiro moyō 網代模様石垣 (Herringbone pattern.) Of all the methods and styles of Karatsumi 空積み Dry masonry the Ajiro moyō 網代模様 is perhaps the strongest when faced with tectonic loads, and needing good drainage...

Again, much of the work of even a basic Anou shū 穴太衆 (Stone Wall Craftsman) or Ishigaki shokunin 石垣職人 (Master Dry Stone Mason) isn't something I could not begin to do justice to in a post entry like this...but for specific questions about Ishigaki sekō 石垣施工 (stone wall construction) I can try my best...If I saw photos of the site, type of stone, CAD and blue print...


Other Useful Links:

The Stone Trust

John Shaw-Rimmington

Jay C. White Cloud wrote:

As example of "how bad it is," in just looking up stuff to share with you about "stone work" I would have to say conservatively 70% of it is not only "bad advice" it is down right "WRONG." The link below was my "first hit" and from materials to technique photos...it is simply hideous...This is why I have become such a nag about folks "vetting information" really well on all manner of things related to "natural" (aka traditional building methods.)

Very bad stone work and advice...just an example what not to do or follow!!!

On this link, what make this bad stone work? Is it just the fact that a concrete mix was used? Or is it also the type of stone? Could that same stone be used with a lime/sand mortar mixture?

Hi Jim,

I am going to take these questions as sincere and not you "pulling my leg..."

Where do I start?? I will cover just the basics as this doesn't really warrant more than that, as the entire linked web page and its advice is beyond hideous...The only positive about it is the fact they are "supporting stone work," but do more damage with their advice than good to the craft...

I will start at the top from the first thing I saw...

No, you do not use concrete...EVER!!! with stone, brick, wood, or anything else you want to keep for very long from rotting or falling apart in such applications...or as prescribed in the article...

The horrid selection of stone (some type of very chausy limestone) in a "boulder" format...Really??...Not for any DIYer as "boulder work" is an advanced from of stone masonry at best...

First photo...Lets see??...We have "head jointing," sloppy mortar lay, gaping joints, poor execution, and bad selection and use of the stone at hand...Worst of all in the photo...concrete mortar and "wedging stones" stuck in mortar!! I would also note the "footer excavation" is all wrong in so many ways I can't begin to describe it...

I would note that I couldn't even "cut and paste" for educational purposes any info to be quoted hear to demonstrate how bad there practice and directions are...I had to "retype it."

In step one the author of the article states:

A stable wall needs a solid foundation -- for this wall, that means concrete. Dig a trench for the concrete foundation about one foot wide and 10 to 12,5 cm deep, running the full length of the seating wall. Use a square shovel to level out the bottom of the trench.

The only part of that which is accurate is a wall of any type requires a solid and structurally sound foundation!!

Everything else is either completely false or grossly inaccurate. A tectonically stabilized stone and gravel foundation is "best practice" for such a wall...Especially in "traditional" (aka natural work.) If one does chose to use a "concrete" (I would select a "natural concrete or geopolymer if I had my choice on a 'spec job') the size the article described was still completely inaccurate. A "concrete footer" at minimum is 300 mm think and would extend, at minimum, 200 mm on either side of the "finished wall" thickness. The "cement" matrix (opc or natural form) should be fiber stabilized and/or have a "non jacking" rebar of carbon or other form...(Personally I just like fiber and it has proven more than strong enough.) Technically the footer needs proper drainage also as they have the concrete going directly onto the dirt....Another huge "no-no!!"

Next photo...we have cement on non mineral soils, no drainage and the worst selection and placement of stone I have ever seen...It has no proper fitting be displayed, no bridging stone application, and is employing the concrete as a "glue" to compensate (I presume) for the atrocious stone work and design of the wall...

Next photo...covers "drop stacking stone" and "fitting smaller ones"...Which it doesn't even follow its own "poor directions" and illustrates perfectly..."what not to do..."

At this point...I just stopped reading, as it's not worth my time now to keep going...I think I have illustrated enough that what folks read on the "web" (me included) needs to be...

Cross Checked

Verified

Compared

and very, very well Vetted and Understood... before ever "copying" or trying to repeat!