Ben Clurk

The fancy transfer scribes, and even compasses to some extent, are surely a pleasure to work with.  However, the only functional difference between a $387,653.26 professional compass and a couple of sticks bolted together is price.  I admit I like the fine adjustment wheel and precision nylon joints on my drafting compass - very easy to use - but I could do just as good a job with a homemade compass whose connections were secured using spare nuts and bolts.

Regarding the fancy levelling armature on a transfer scribe, a piece of coathanger and a 50¢ spirit level could accomplish the same thing.

If you have money to burn, professional/engineered tools often have little features about them that make them much easier to use.  The premium is all about convenience.

I would have preferred to stick with straw because it is proven to be a great match, but I don't have access to nearly enough to do anything with.

I was thinking specifically of shaving down some of my most crooked logs, taking care to get nice, long shavings with my drawknife, and then further splitting them with my pocketknife.  A slow approach, no doubt, but I am afraid to trust rammed earth because the walls will be going on a very crude stone foundation that is bound to heave all over the place in the winter.

I did a small test block of pure subsoil without fiber a while ago and was impressed with the results.  I'll take a larger sample and do some more blocks with the wood fiber.

Thanks for mentioning the swelling issue; I hadn't really though much about it.  I will try saturated, green (fresh-cut tree, ambient moisture), and seasoned to see if there is a difference.  Saturated, flexible fibers seem like they would be best, if possible.  I think I'll also try it with heartwood, for extra decay resistance.

As soon as I have a dry day I'll go out and dig some more for the tests.

Rebecca Norman:  Have you tried long fibers of wood rather than just wood chips?  I am imagining something like 1/8" or smaller, a minimum of 12" long.

Sebastian Köln's idea sounds really good for a nice durable surface.  I might try to experiment with something like myself eventually.

From the way you described your project, I have the impression that you might be dealing with storm water rushing across the site.

I was recently reading about the restoration of old stone bridges and the author talked about rushing water's amazing ability to find any little crack to get back behind the stone and erode the soil.

I'm sure you won't be dealing with a massive deluge like a bridge over a large stream, but any amount of water can cause erosion as it washes across a surface...So I would recommend a homogeneous water-resistant mix.  I would definitely NOT recommend a shell of portland cement as it will only cause problems for the cob it is protecting, as when people try to 'stucco' an adobe house with concrete.

Lime would be the way to go, which you can make from wood ash.  It is unique in that unlike portland cement it will chemically react with the clay in the cob rather than just be weakened by it.  And you won't have a bland gray mass, but just a lighter version of your cob's natural color.  Keep in mind, though, that lime takes a very, very long time to really do its thing because it relies on gas exchange to work rather than water, like portland cement.

For info on making lime from wood ash, search YouTube for 'Primitive Technology Pot Made of Wood Ash'.  Wood species seems to be important for calcium content, so you might want to try different flavors to see what works best.  The guy in the video just made basically a mortar mix with lime and sand, which would probably be the quickest way to tell how well your ash is doing.

Lime is supposedly pretty picky about firing temperature, but I think in the case of wood (as opposed to limestone), the minimum temperature to produce clean, light-colored ash would be a safe bet.  Overfired, or 'burnt', lime, isn't as chemically reactive, but again I think you would only see that with the temperatures used with limestone.

Man.  I can't say anything quickly.

To clarify about the stone and slope, the 'surrounding 10' will be soil with grass.  I am worried about frost heave grabbing the stones and pulling them out of place.  The foundation will be about 2' deep with drainage to daylight, the foundation possibly reaching out as far as 2' beyond the wall to keep it stable.  I'm not sure.  It won't be pretty.  The surrounding slope will be compacted thoroughly to avoid settling.

I am trying to get a house built so I won't have to spend next winter in my tent.  Materials must all come from on-site, aside from some bits of hardware, e.g. nails.

I'll just lay it out for you.  Please let me know what you think.  Any suggestions are welcome.

- - -

The house will be a cruck frame with cob walls, a very crude stone foundation, and white oak shakes for roofing, 45° pitch.  The floor will be packed clay over rubble.  The ceiling will be cob as well, amply supported but no thicker than necessary in case it gets wet, probably flat but I like tall N windows, so it's hard to say for sure.  No plaster under the rafters - I want to be able to see the roof for inspection.  It will be heated by a large mass stove.

The issue is with the walls and foundation.  I had very good luck with a small block I made from sifted, undoctored subsoil from the site where I'm already planning to make a sand filter for roof runoff collection, so I'm pretty happy with that.  I have no access to straw without shelling out money, but I can make long strips of wood fiber with my drawknife, so I'm going with that.  Laborious, but it will work.  I hope.

I have tons of stone on my property, but it is all little misshapen chunks of chert, rarely larger than 8" at its widest dimension and with no real grain to it but plenty of random fractures.  The best stuff is hard and glassy, but more than half of it is deeply weathered.  With this in mind, I am hoping to go for more of a mounded foundation, sloping heavily outward for stability and with a slight drainage slope in the surrounding 10', maybe 2:12 or something like that.  I can't have too much or the frost heave will be really bad.

So...yeah.  Very crude foundation of small, irregular stones and cob with wood fiber.

Can this last at least long enough to regenerate the timber?  What do you think?

No, there will be no insulation, and concrete is not an option.  I could wind up doing something pretty crazy, though, like glass for the windows, but not for a while.

'Primitive Technology' on YouTube has a couple of really good videos on making lime from ash.  In one of his videos he fired bark (I think species matters), then took clean white ash, mixed it with sand, and formed a brick.  He noted that it warmed as he was mixing in the water, which means it was slaking without the need for any extra processing.  After the brick had set up he immersed it for 24 hrs with no degradation!  How nice and simple.  As I understand it, hardwood ash tends to have a higher calcium content.  The specific use of bark in this video makes me wonder if maybe bark contains the best concentration in the tree.  That would be great because I am busy stripping red and white oak logs and I don't want to sacrifice any of the wood itself on the off chance that I'll wind up with lime.

To see the video, search YouTube for 'Primitive Technology Pot Made of Wood Ash'.

He has lots of other good videos!

I agree that you would be fine with the roots.  As a ridiculously obvious reason why straw isn't mandatory as the fiber ingredient, you can toss it in the compost and it will rot just like anything else.

I think insect infestation may be a valid concern when deviating from straw, but once again as long as the wall remains dry I don't think insects will want to bother trying to gnaw through hardened clay.  I think that's part of the reason why you strip a log - it helps to keep the surface from catching and soaking up too much water, which in turn keeps the fibers tough and hard to chew through.  I could be wrong about that, though.

It seems like it would be perfectly feasible, minus the whole money part.  You might want to look into galvanic protection to handle corrosion.  You can use sacrificial paints as well as anodes connected to a good conductor, like moist subsoil, to make a steel structure last pretty much indefinitely.

Breathability depends mainly on surface exposure, so if you could provide ventilation for the core of the wall, for instance unlined ducts molded into the cob with some provision to ensure air exchange, it should theoretically be possible to keep it dry, even passively, by moving the exchange site from the covered face to a network of interior surfaces near that face.  An inlet and outlet would be necessary of course.  It might be possible to stimulate the airflow with a solar chimney, too.  It wouldn't be a bad idea to embed some moisture sensors to keep an eye on it, just to be safe.  This would definitely interfere with the thermal properties of the wall, too.  Probably.  Definitely.  Maybe.

For breathability all the way from one side to the other, it's really more of a side benefit of cob than anything because there are half a million ways to achieve ventilation that don't require cob.  If the ducts for exhausting moisture can be designed to function equally well for ventilation, that's just icing on the cake!

Steel being what it is, you would need to add a good mechanical attachment method to the plates of steel.  Rebar tack-welded to either face comes to mind as a fairly conventional solution.

As far as cob as a material goes, I think it has so much more potential than current methods provide.  Because it is so cheap you can make it as thick as you want, and wind up with ample structural capacity to boot.  It would certainly be far cheaper to provide more roof to cover a thicker cob wall than to embed 3/4" steel plate, and you would have the year-round temperature regulation of a berm without the moisture considerations.  The wall could rest on a pad of stone, gravel, or concrete and be inherently stable against frost heave.  You could have fancy built-in nooks with your windows without significantly weakening them.  You could have secret passages in the walls, and offset trick mirror windows, and deep candle-lit relief sculptures, and, and...

I don't know how official you want to be about it, but a simple slow sand filter seems to be one of the easiest ways to go, although the details of the process could take some work to get right.  From what I understand, the process relies on biological growth in the medium (sand), gradually filtering the water as it travels downward through it.  I have no idea how the chemical/biological aspects serve to purify the water.  They just...do.

It takes a fairly large volume of sand to supply a large number of people because the effectiveness of the filter relies on the percolation rate, which should be slow and I'm pretty sure continuous.

But for quick and easy I've been collecting rain from a canvas tarp directly into a pair of plastic storage tubs for the past six months and I seem to be still alive and healthy.  My only precaution is that I leave the tubs' lids on anytime it isn't raining to keep out insects and sunlight.

There is a layer of sediment, including dirt and leaves, at the bottom of crystal clear water with no noticeable flavor.

From what I understand, if I were to build an actual cistern down in the ground I could fill it up, let it sit for a period of time (?), and then draw from settled, largely self-sterilized water.  I think this is because micro-organisms gradually consume all organic material and then each other.  I'm sure dipping into the sediment would be a bad idea, since that's where any remaining goodies will be.

I admit that I could easily contract a disease from deposited bird droppings on my tarp and I really don't know what sorts of chemicals were used in my tarp.  So, you know.  I might die.  But I think the danger of raw water collection is largely overstated, provided you take some basic precautions and expect your immune system to go through a period of acclimation after you begin consuming water at a new location.  I think I had the squirts on and off for the first month, but ever since I have had no problems.