Can we talk about wood chip clay?

We're hoping to start building our "dream house" on our property next year. Definitely want natural (breathable) materials for the infill (skeleton will be timber frame). Originally wanted cob, but it's labour intensive, needs a good long dry time, and I worry that it's not the best insulator. Thanks to Dale I've learned about woodchip clayslip construction and am eager to learn more but finding little reference to it on the net. A local architect who has done lots of cob, etc here says that light Clay, or "chip'n'slip" is popular here. I'm assuming she means woodchip.

Some questions: how thick do the walls need to be for a mild climate such as Vancouver Island? How fast does it set (I.e. how long before you can take off the form to use elsewhere? Why do I not see more info ( am I just not finding the right sites?)?

TIA!

umm drying time of cob is a function of temp and wind. you are in the cowichin valley. you should have plenty of both unless you are so far under the edge that you dont see the sun till the evening. Chip cob is going to take longer to dry than sand clay and straw it just sucks up the water into the chip. if you have a tractor you can make lots of cob very quickly and you dont have to dink around with a it you can do trod cob.

if you are doing infill i would suggest you use light straw clay. it can be stacked vertically shrinks little when the proportions are correct and usually has a built in dry indicator in the form of grass seeds that will sprout then die as the mass dries out. you can do straw clay in 4 inch or thicker walls its got ok insulation and ok thermal mass. the echo nest designs are all based on it and having been a few i would recommend it. where you are at i would recommend Cob bale even more. it builds fast and is R50 or so. you can opt to put the cob on the inside or the outside or both. plaster goes on nice and it is weather resistant. wide eves makes it more so. (you should have wide eves at any rate for any house to keep the rain off the walls) Ah well. those are options. all of them are labor intensive the bale being to me the least and fastest going up.

Mariah Wallener wrote:How fast does it set (I.e. how long before you can take off the form to use elsewhere? Why do I not see more info ( am I just not finding the right sites?)?

TIA!

Hi Mariah,

When I built my chip slip structure, I was able to move the forms up immediately. Two things though. The mix has to be tamped in reasonably tight and it can't be too wet. You use just enough clay slip to cover the wood chips and no more.

That said, my forms were only about 2' tall...only because that's the height of the plywood I had on hand. My walls were no taller than 7' also. Based on my experience though, I see no reason why a 4' tall form could not be used in a 6"+ thick wall with heights up to 8' or more.

As you already stated, there's very little written info on the technique. I first learned about it in "The Art of Natural Building". Still, there's only a page's worth as I recall.

rusty

Ianto likes it for some things; its no magic pill and should be used in some applications and not others. like any form of cob.

Chip Slip Sauna

http://www.dayonedesign.org/blog/page/1

ive got a chip slip out house in progress, ill see if i can post some pictures. its on hiatus for the winter, i havent poured the chip yet.

Straw is expensive on Vancouver Island and of lower quality than straw from drier areas. Wood waste is abundant and free. That seals the deal for me. I will use straw sparingly.

I made some test blocks where I mixed slip over relatively large, dry chips. The chips were being sucked dry of moisture as I stomped them into place. If I had let this material stand for an hour It would have been difficult to work with. So, I think limiting mix tank time is important as it allows for utilization of the material while the center of the chips are dry and thus the process uses less water. For me it's not structural so no need to squeeze out every air space.

Air flow is vitally important in fostering evaporation. That's why plastering is delayed. The rough surface of freshly placed chips give a large surface area exposed to drying sun and wind. I'm on a high, dry south facing site with perfect solar exposure. The north side of a hill near sea level would have slower evaporation.

I'm hooked on the idea of building the heating system early on in the project so that it can help dry the chips. I may also burn homemade charcoal in several locations around the interior to speed things up. I plan to postpone plastering for 6 months or more. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Rusty, what can you tell us about your wind speed, solar exposure, temperatures, and relative humidity while yours dried ? Did you heat the building during dry time ? How long before you plastered ? Was there any mold ?

I have only seen wood chip clay in use once, as insulation in a milk house section of an old barn near Kitchener Ontario Canada. The area was settled by Germans. There is some straw clay attic insulation in some of the old stone farmhouses. My only other experience with it is through the internet and my own test batches.

Mariah Wallener, let's race. If I get all of my paperwork in order first, you're invited to spend some time at my place to see how it works out. If you're ready first I'll lend a hand and any equipment that I have at that point. On your marks, get set ---- BUILD.

Ernie, we've been here through two summers now. First one was hot and dry, but last summer was super late in arriving, didn't last long, and wasn't as hot as the year before. It's a summer like that that makes me wonder if we'll have enough time for full cob to dry out. Not that it would be awful if it didn't...at least we have a place to live while building.

Jamie, that's awesome! Looking forward to hearing more about how the wall-building process goes.

What I'd like to see on this thread is a list of pros and cons. I get that chip-slip is less labour intensive than cob. What about insulation factor? Drying time?

And hey, could you put wood chip slip on either side of straw bale as some do with cob? Or is that just fibre overkill?

I would say yes with the qualification that Cob bale is chinked with cob in all the joints. (the cob does not touch the inside cob so you have a thermal break and not a bridge). the bale is stacked on edge and chinked with cob so the whole wall is stable from the start. then if you wish and i always do, a lattice of bamboo, pig fence, hazel withy, willow withy, rebar. ETC is sewn to the faces of the walls. Making them into a single stable unit. this structure is then Plastered on the outside with 4 inches of plaster (2 inches base coat, 1 inch scratch coat, 1 inch finish or three inches base and scratch and 1 inch finish coat). this smoothes and seals up the outside, typical of bale houses as built now. inside is the place things get interesting, the bale wall is slipped and 6 to 8 inches of cob are applied before plaster to add thermal mass to the structure then the space is plastered normally.

this gives you 8 hours of thermal mass to keep the inside temp as steady as possible and the insulation to maintain a significant difference in temp from the inside to the outside. it also helps transport water vapor through the walls stabilizing the bale at a specific moisture content (due to to the capillary action of the cob and plaster) While this method takes a little longer than normal bale construction it is well suited to the cold damp conditions found in the pacific north west and is especially suited to the colder climates.

Dale Hodgins wrote:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Rusty, what can you tell us about your wind speed, solar exposure, temperatures, and relative humidity while yours dried ? Did you heat the building during dry time ? How long before you plastered ? Was there any mold ?

)

I built in a highly protected area nearly void of wind. Slight breezes, yes...but very seldom. There was some solar exposure but the surrounding trees kept it down...perhaps to 3-5 hours/day at best and not on all the surface area. Humidity would have been low (S Idaho, desert), no rain. Night time temps would have been around 50, day time between 75 and 90. I ran a couple of small space heaters inside for a few days. Re time before plastering, I had posted before that it was 3-4 wks. Giving it a little more thought, it could have been up to 6 weeks. I detected no sign of mold...but I added a small amount of borax to the slip for a preventative measure. Keep in mind too that this chip slip wall was only 3.5" thick....before plastering.

EDIT: Let me note that the wood chips I used were mostly small.... and dry. For size, refer back to the photos I posted in this thread: https://permies.com/t/12319/green-building/Strawbale-Pacific-Northwest-anyone#112754

Mariah Wallener wrote:

What I'd like to see on this thread is a list of pros and cons. I get that chip-slip is less labour intensive than cob. What about insulation factor? Drying time?

Regarding the insulative value:

There is no scientific data on this type of wall....but, being that the R values of different woods are known, we can come up with a pretty good idea. Hardwoods have an R value of ~.91 per inch; softwoods ~1.25 per inch. But, being that we are working with wood chips, coated with clay slip, the walls we're discussing aren't quite solid wood. The clay slip will not have enough insulative value to even mention here. So, the per inch R value of a chip slip wall will be slightly less than if it were a solid wood wall.

Lets assume your wall was 12" thick...and a solid softwood. That's only an R 15 which, is slightly better than a 2x4 wall insulated with standard fiberglass batts (3.5" batts= R11).

Per inch, a chip slip wall will not have much insulative value.

So from what Rusty says it sounds like wood chip slip is not really much better than cob, re: insulation-wise.

Ernie, could you elaborate on what you mean by "chinking with cob in the joints"? I understand what you mean about not wanting the cob to join to the inside and thus create a thermal bridge; makes sense. Wondering what that looks like around posts (see below).

I must say that I like the idea of straw bale "sandwich" with cob as the "bread". Say you have a timber-framed house, I've often wondered whether you put the vertical posts on the inside wall or outside, since they are thinner than a bale of straw. I"m guessing the inside so that you can see them (they add such beauty to interiors). So I guess you need to cut some of the bales that go around the posts. How does one handle the interface between wood post and strawbale/cob/plaster wall?

Mariah Wallener wrote:So from what Rusty says it sounds like wood chip slip is not really much better than cob, re: insulation-wise.

Ernie, could you elaborate on what you mean by "chinking with cob in the joints"? I understand what you mean about not wanting the cob to join to the inside and thus create a thermal bridge; makes sense. Wondering what that looks like around posts (see below).

I must say that I like the idea of straw bale "sandwich" with cob as the "bread". Say you have a timber-framed house, I've often wondered whether you put the vertical posts on the inside wall or outside, since they are thinner than a bale of straw. I"m guessing the inside so that you can see them (they add such beauty to interiors). So I guess you need to cut some of the bales that go around the posts. How does one handle the interface between wood post and strawbale/cob/plaster wall?

Per inch, chip slip would have more insulative value than cob...probably by a fair margin. However, that's not saying too much.

Re the location of the posts, they can essentially be put anywhere you want...totally independent from the bales, inside or out....or set within the bales, either completely concealed so they are plastered over or so that they are partially exposed. There are disadvantages and advantages to each of these methods. In the latter way, you would simply run the wall plaster right up to the post (you can mask the posts to keep the plaster off, just as you would when painting).

just like chinking between logs. you stuff cob in to make a wedge between all the horizontal and vertical joints, this stabilizes the bales and gives you a good grip for cob or plaster.

I prefer the posts inside 1/3rd to half in the wall, the way to attach the cob to the post is to sink nails partially into the post where it meets the cob or make some dead-men that are in the wall and strap around the post attaching it to the wall, a combination of both is what i like. wrought iron straps and the nails where i cant see them. The cob mix if done right wont shrink very much and you just fill the bit it shrinks in with cob. the plaster should not shrink at all depending on the type of plaster. Obviously a clay dung plaster will shrink. as for cutting bales why would you when you can run the cob up to them
I probably sound like a salesmen or something.

Just to be clear. In my previous post, I was referring to a straw bale wall with plaster only. No cob.

Rusty Bowman wrote:

Mariah Wallener wrote:

What I'd like to see on this thread is a list of pros and cons. I get that chip-slip is less labour intensive than cob. What about insulation factor? Drying time?

Regarding the insulative value:

There is no scientific data on this type of wall....but, being that the R values of different woods are known, we can come up with a pretty good idea. Hardwoods have an R value of ~.91 per inch; softwoods ~1.25 per inch. But, being that we are working with wood chips, coated with clay slip, the walls we're discussing aren't quite solid wood. The clay slip will not have enough insulative value to even mention here. So, the per inch R value of a chip slip wall will be slightly less than if it were a solid wood wall.

Lets assume your wall was 12" thick...and a solid softwood. That's only an R 15 which, is slightly better than a 2x4 wall insulated with standard fiberglass batts (3.5" batts= R11).

Per inch, a chip slip wall will not have much insulative value.

Um.. this neglects the most significant insulation component in using any shredded material: air gaps.
If the chip-slip mix is compacted enough to eliminate all air gaps, then you would have a value like cordwood or 2x4 or cob.
But even the straw-clay I've seen has air gaps between the straws, as well as within the straws.

Some advantages over wood or cordwood:
- any air voids add to the insulative value,
- you have very few through-wall bridges or voids like you can in cordwood and 2x4 constructoin, so heat transmission is slowed.

Try setting up some test blocks with a propane torch on the outside, or ice cubes on the inside, or something to give you a measurable temperature difference.
Compare side-by-side with known materials like cob or light straw-clay, for thermal transmission. See if it feels right. Just put your hand on it once it's dry: it shouldn't 'feel' very hot or cold, even if it's frozen, compared to a denser or more conductive material.

Might also be able to incorporate something to boost the insulation value, like perlite in the chip mix or exterior scratch-coat plaster. (The weather coat should not have perlite as it can soak up too much water, but straw is great for exterior plasters.) You could do this on north walls or windward walls, and let the sunward walls catch solar heat.
Or even charcoal. That would be a new use for biochar! I've seen it made of Himalaya blackberry canes or other invasive weeds, and if only lightly charred (to prevent re-growth) you'd get the hollow cane structure too. Should be able to incorporate some proportion of charcoal in chip-slip, especially if it still contains some unburnt fiber.

You might also see if there are other local ag wastes available that offer air space, like rice or oat hulls. Or hollow-stemmed chip materials like elderberry, mullen, weed canes, etc. Like straw but rougher. More work, but you might find a chipper who gets this kind of work from time to time. If you let them dump all their truckloads at your place (one of the reasons it's free is it saves them a drive when they are clearing utilities or whatever in your area), you can high-grade for biochar or hollow-stalk materials, and pull them off the piles before they start to rot down.

Have to keep reading to see if there's comments from people who've actually built with it, about insulation value.

-EKW

SHORTENING DRY TIME

PLANT IT WITH TREES---- A few years ago I attempted to propogate some trees by stripping a few inches of bark partially off some branches and poking them several inches into wet soil in 5 gallon plastic buckets. It was a collosal failure. None of them grew roots. It was summer rather than spring when this might have worked. But the trees looked perfectly fine for about a week. I had work to do and I completely neglected them. Within 10 days, the soil had dried out and they lost their dry leaves.

This presents a question: Did the soil dry out just from the surface evaporation on an otherwise impervious container ? Or, were those branches sucking the moisture out ? Without roots, a branch won't draw water as quickly as a tree of similar size would but since it took quite a while for the leaves to dry, the cambium layer must have taken up some water. I'll conduct a test with 2 pails of dirt with identical soil and moisture wtih the leafy stick as a variable.

PLANT IT WITH BUCKWHEAT or alfalfa or ? ---- This is similar to the weed and wheat seeds that sprout from straw. Little clay balls pressed into crevices on the surface of the new wall would make more efficient use of seed than simply mixing throughout. Sprouts 6 inches deep in dense material are unlikely to reach the surface.

Supposing the sticks do work, they could be plucked out when dry and this would leave little holes to be filled at plastering time.

Has anyone here planted seed on cob, straw clay or chip clay ?

Erica Wisner wrote:

Rusty Bowman wrote:

Mariah Wallener wrote:

What I'd like to see on this thread is a list of pros and cons. I get that chip-slip is less labour intensive than cob. What about insulation factor? Drying time?

Regarding the insulative value:

There is no scientific data on this type of wall....but, being that the R values of different woods are known, we can come up with a pretty good idea. Hardwoods have an R value of ~.91 per inch; softwoods ~1.25 per inch. But, being that we are working with wood chips, coated with clay slip, the walls we're discussing aren't quite solid wood. The clay slip will not have enough insulative value to even mention here. So, the per inch R value of a chip slip wall will be slightly less than if it were a solid wood wall.

Lets assume your wall was 12" thick...and a solid softwood. That's only an R 15 which, is slightly better than a 2x4 wall insulated with standard fiberglass batts (3.5" batts= R11).

Per inch, a chip slip wall will not have much insulative value.

Um.. this neglects the most significant insulation component in using any shredded material: air gaps.
If the chip-slip mix is compacted enough to eliminate all air gaps, then you would have a value like cordwood or 2x4 or cob.
But even the straw-clay I've seen has air gaps between the straws, as well as within the straws.

Some advantages over wood or cordwood:
- any air voids add to the insulative value,
- you have very few through-wall bridges or voids like you can in cordwood and 2x4 constructoin, so heat transmission is slowed.

Try setting up some test blocks with a propane torch on the outside, or ice cubes on the inside, or something to give you a measurable temperature difference.
Compare side-by-side with known materials like cob or light straw-clay, for thermal transmission. See if it feels right. Just put your hand on it once it's dry: it shouldn't 'feel' very hot or cold, even if it's frozen, compared to a denser or more conductive material.

Might also be able to incorporate something to boost the insulation value, like perlite in the chip mix or exterior scratch-coat plaster. (The weather coat should not have perlite as it can soak up too much water, but straw is great for exterior plasters.) You could do this on north walls or windward walls, and let the sunward walls catch solar heat.
Or even charcoal. That would be a new use for biochar! I've seen it made of Himalaya blackberry canes or other invasive weeds, and if only lightly charred (to prevent re-growth) you'd get the hollow cane structure too. Should be able to incorporate some proportion of charcoal in chip-slip, especially if it still contains some unburnt fiber.

You might also see if there are other local ag wastes available that offer air space, like rice or oat hulls. Or hollow-stemmed chip materials like elderberry, mullen, weed canes, etc. Like straw but rougher. More work, but you might find a chipper who gets this kind of work from time to time. If you let them dump all their truckloads at your place (one of the reasons it's free is it saves them a drive when they are clearing utilities or whatever in your area), you can high-grade for biochar or hollow-stalk materials, and pull them off the piles before they start to rot down.

Have to keep reading to see if there's comments from people who've actually built with it, about insulation value.

-EKW

Air gaps are something to take into account. In my case though, there were not many gaps. In my test walls, the sections not compacted well were weak and crumbly. I'm guessing that clay-straw (light clay, straw-clay, etc) wouldn't need to be compacted quite so tightly given the length of the strands of straw versus the short lengths of wood chips. Straw would be more akin to rebar in concrete and the chips akin to aggregate, roughly.

Mixing in perlite is an interesting idea. At first glance, pumice and cinders would seem even more of a logical choice...but they have a lower R value than wood. Loose perlite is roughly 2.7/inch though. Not bad!

In theory, the straw in plaster would boost the wall's R value...but in reality, I'm betting one couldn't mix in enough to boost the R value enough to mention. What's enough to mention though? I don't know.

Long pithy plants like you mention is an interesting idea as well. A mix of of something like elderberry along with perlite might produce a wall with very respectable R value. Mullein is weaker but I bet one could still get better insulative value with it over straight wood chips. Probably moot though unless one knows of mullein fields begging to be cut down. The elderberry would have enough structural strength for decent compaction without collapsing and ruining its theoretical R value. I like it. Obtaining enough elderberry is far more realistic than enough mullein... though it would even require a big stroke of luck... or two....

Once mixed with clay, perlite will loose much if its effectiveness since the clay provides a thermal bridge.Part of what makes pearlite effective is the air it encapsulates. I don't know what the adjusted R value would be. Larger flattish material would be more likely to produce thermal breaks even if the material creating that break is less insulative than pure perlite.

Part of my reasoning for going 12-16 inches thick with permanently encapsulated bracing is so that I can attain structural integrity without needing to squeeze all of the air out of the mix. I figure that the extra work in placing more material will be somewhat offset by being able to place material quickly without all the tamping. The extra effort to go thicker would be less labour intensive than hunting down and processing specific canes for their insulative properties.

CONCERNING WOOD CHIPS --- Chips that come off of a branch chipper are cleanly cut and tend to lie flat to other chips when piled. Chips that have passed through a hammermill tend to be roughly torn and they are sometimes stringy as the wood separates along growth rings. These chips are more resistant to packing and should produce a more airy mix. I plan to use hammermill chips along with coarse sawdust packed just enough to make it hold together. This will produce billions of little air spaces.

Erica Wisner wrote:
If the chip-slip mix is compacted enough to eliminate all air gaps, then you would have a value like cordwood or 2x4 or cob.

-EKW

Actually, when going by raw R values, a compacted chip-slip wall should have more insulative power per inch than cob. Consider that a two-string bale laid flat only has an R value of 26 (according to tests at the Oak Ridge National Laboratory). A two string bale of 18" would then equate to an R value of 1.44/inch. Considering softwood has an R value of 1.25/inch, a cob wall wouldn't even be a "cob" wall any more if it had enough straw in it for an R value/inch equivalency.

Of course, that's going by the numbers, by the raw value....by the books. The real feel, combined with many other factors, can sometimes tell a different story......

Rusty
I dont Think the R value on a bale can be the same as a log.

Ernie Wisner wrote:Rusty
I dont Think the R value on a bale can be the same as a log.

E D I T:

Ernie,

Just stating numbers arrived at via scientific research. Not mine. Point being here, the R value of straw is not nearly as high as thought early on which, is pretty well documented now. Broken down, 1" taken from a flat bale of straw barely has more R value than does 1" of softwood. Does that mean a completed straw wall would not have a noticeably higher R value than a solid wood wall of the same thickness and finish? Not necessarily. And that's why I said "the real feel, combined with many other factors, can sometimes tell a different story". Looking at the numbers derived from scientific research though, can give us a quantifiable place to start when comparing materials.

Reading this all with interest...

Ernie, you don't sound like a salesman but you are making a good case for strawbale cob. For one thing, I can see that having only 4 inches, say, of cob on either wall would require a lot less labour than doing a 18" thick cob wall. And, as you said, it means not having to cut bales. I thought of another advantage - running conduits for electrical, etc - I would feel better having that run through cob than strawbale.

As i am doing scientific research i would question how those numbers where obtained. the air space in a bale unless the bailer was set for the highest tension its capable of would be considerably higher in the bale.
if they tested 1 inch from the edge by cutting it off i would agree that it is the same r-value that would be a duh cause it does not take into account the whole of the object.

Always question the methodology of a scientific study, thats why they put the method on the papers. most times these studies are pointed at a specific thing so i would ask what the theorem is that thy where trying to prove.
I will almost bet this was a study funded by some housing folks and the theorem was developed for the researcher. "Note: In most American literature regarding straw bale building, the R-values for strawbale walls are stated to be between R-30 and R-48. This is misleading as they use a different calculation system for their insulation values compared to the system used in Australia." ( http://www.strawtec.com.au/page.php?id=5 )

I think folks need to see multiple research. Straw tech is a pretty darn good resource.

Mariha
the best way to run electrical in cob or bale in my opinion is to make a box behind wainscoting trim that you can take the trim off and expose the whole electrical system. this makes it easy to see and if there is any problems or changes you want to do later you can without destroying half the house. since I was taught to think in terms of centuries for cob and bale houses i tend to try and think what will make it easy for the building to be remodeled 50 years from now. then i make those provisions into the house structure. wainscoting means you dont beat the wall plaster to death with chair backs and it gives you the option of running your net, phone, audio. plumbing and electric in a way that allows you access it, while being rather decorative in the house. Any how you to might want to take a look at that link.

Ernie Wisner wrote:As i am doing scientific research i would question how those numbers where obtained. the air space in a bale unless the bailer was set for the highest tension its capable of would be considerably higher in the bale.
if they tested 1 inch from the edge by cutting it off i would agree that it is the same r-value that would be a duh cause it does not take into account the whole of the object.

Always question the methodology of a scientific study, thats why they put the method on the papers. most times these studies are pointed at a specific thing so i would ask what the theorem is that thy where trying to prove.
I will almost bet this was a study funded by some housing folks and the theorem was developed for the researcher. "Note: In most American literature regarding straw bale building, the R-values for strawbale walls are stated to be between R-30 and R-48. This is misleading as they use a different calculation system for their insulation values compared to the system used in Australia." ( http://www.strawtec.com.au/page.php?id=5 )

I think folks need to see multiple research. Straw tech is a pretty darn good resource.

Ok, so if the Oakridge study is tainted, what do you believe the real R value of straw is....and how did you arrive at or get that figure? I checked out Straw Tech but saw nothing as far any study methodology.

Just to be clear, I'm not trying to devalue the use of straw as a building material at all. I've grown wheat and baled the straw, worked with it and designed around it. I advocate it....even if it did only have an R 26...which, considering the continuity of the wall, still offers superior insulative qualities over a standard 2x6 wall, not to mention all the other great things about straw. I'm just questioning whether a number derived from a Master's thesis two decades ago should be the last word on the subject.

Don't forget that the original intent, if I remember correctly, is to build a sustainable house for not a lot of money. If quality straw bales need to be trucked in from the dry side of the mountains and across the strait, I think that the costs are going to jump up appreciably. Appropriate technology includes the utilization of what is available locally. There is certainly more than one way to skin a cat, or so the saying goes, not having personal experience in the matter. Wood chips and sawdust seem to be what is available locally in this case; unless there are other grasses or reeds available on Vancouver Island at a low cost (phragmites, cattails), that could be used in a straw clay application.

Have you looked into adding MgO to your slip? It is supposed to do a number of positive things when used with straw clay, wood chip clay or basically any cellulose and a clay slip.

One of Buckminster Fuller's many failed schemes, and one of his first, was a business with his brother, or brother-in-law, or perhaps a cousin, I don't quite recall, building homes out of excelsior (shredded aspen) and cement. I don't know if he used Portland cement or an MgO based cement, but the walls started disintegrating after a few months (major bummer). There are cellulose cement products (mixes and pre-formed) available that have an excellent track record so I suppose it is just a matter of getting the mix right.

Search for "straw clay" and "MgO" to get an idea of what has been, and is being, done.

Rusty Bowman wrote:

Ernie Wisner wrote:As i am doing scientific research i would question how those numbers where obtained. the air space in a bale unless the bailer was set for the highest tension its capable of would be considerably higher in the bale.
if they tested 1 inch from the edge by cutting it off i would agree that it is the same r-value that would be a duh cause it does not take into account the whole of the object.

Always question the methodology of a scientific study, thats why they put the method on the papers. most times these studies are pointed at a specific thing so i would ask what the theorem is that thy where trying to prove.
I will almost bet this was a study funded by some housing folks and the theorem was developed for the researcher. "Note: In most American literature regarding straw bale building, the R-values for strawbale walls are stated to be between R-30 and R-48. This is misleading as they use a different calculation system for their insulation values compared to the system used in Australia." ( http://www.strawtec.com.au/page.php?id=5 )

I think folks need to see multiple research. Straw tech is a pretty darn good resource.

Ok, so if the Oakridge study is tainted, what do you believe the real R value of straw is....and how did you arrive at or get that figure? I checked out Straw Tech but saw nothing as far any study methodology.

Just to be clear, I'm not trying to devalue the use of straw as a building material at all. I've grown wheat and baled the straw, worked with it and designed around it. I advocate it....even if it did only have an R 26...which, considering the continuity of the wall, still offers superior insulative qualities over a standard 2x6 wall, not to mention all the other great things about straw. I'm just questioning whether a number derived from a Master's thesis two decades ago should be the last word on the subject.

I think most labs numbers are tainted and i know why they are tainted. no big deal I arrived at the value by averaging all the numbers i have seen over the years. it's the only way to go with all the data suspect.

you can write to straw-tech and ask what the methodology was. And for the record i think the numbers there are suspect as well.
I have been in labs and collage to much to ignore the bias in the numbers. i just live with it and remain skeptical What i do is average all the numbers folks throw around and i think thats a real close approximation to the real deal.

Sorry Rusty i am not saying you are wrong i am just saying the numbers dont make sense and i would check the data. there is no way a bale can be the same R value as a log. the densities. are different enough to make that datum suspect.

Ernie Wisner wrote:
I think most labs numbers are tainted and i know why they are tainted. no big deal I arrived at the value by averaging all the numbers i have seen over the years. it's the only way to go with all the data suspect.

Sorry Rusty i am not saying you are wrong i am just saying the numbers dont make sense and i would check the data. there is no way a bale can be the same R value as a log. the densities. are different enough to make that datum suspect.

No worries, Ernie. I'm not saying you are wrong either. I just think it's always helpful to have as much info as possible on the table so it can be sifted through for some reasonable point of reference, within context.

At the risk of sounding like a broken record, I will say it again; R values don't always tell the whole story. Even if the numbers I posted are correct, that doesn't mean straw wouldn't make a superior house insulation. I believe straw would be better........but I would not feel comfortable being cocksure about that. After all, I have never been in a home built with solid rectangular timbers the size of a straw bale....

I'm sorry if I got this thread off track. Andrew Parker is correct and has what I believe is an idea worth looking into with Cattail. I'd add Bulrush Tule to that as well. From the standpoint of insulative value in a wall like we're talking about, I believe those two would be hard to beat, particularly the Tule. Not sure about their availability in the area of question though. Has anyone used Cattail or Tule in this type of wall construction?

There was some speculation about bale density and R value. ---- The insulative value of any cellulose material is hugely influenced by the air spaces that it encapsulates. With bales, those spaces tend to be elongated due to the long skinny nature of the stalks. If these spaces could be filled with finely ground cellulose insulation ( the re-cycled newspaper variety ), the R value could be improved.

I have blown thousands of sq. ft. of this stuff into walls already containing large granule vermiculite, poorly fitted fibreglass, lumpy rock wool that was placed by hand and wood shavings. The fine powder sifts around and improves materials which are too porous. Clogging of the blower hose is a problem which is remidied with the machinery being set at the highest air setting. This might work to some degree to improve the lightest 2 string bales. Really dense 3 string wheat or rice straw would surely clog the nozzel, even with extra air added. This is a process which would reach a state of diminishing returns rather quickly.

It's probably only worth trying on a non load bearing wall of light 2 string bales after the first scratch coat of plaster is applied. An added benefit is that it only takes a small amount of this borax treated product to deter rodents.

I built a straw-clay house with 12" walls. It takes about one week per inch to dry if you have dry weather - more if you have humidity / precipitation. So that means about six weeks for a 12" wall since the walls dry from both sides.

I imagine woodchip-clay walls would be similar w.r.t. drying time - maybe faster due to more pore space. Maybe expect longer for BC though...

Here in coastal B.C. we get some nice hot dry weather most summers. By September the evaporation rate drops off and our winters are wet. I like the idea of a post and beam structure with roof being finished before any clay based portions of the job commence. Infill can go into a second year if the weather turns.

building in the PNW I follow what i call the "Roof first principal" what this means is; I build a roof and stick it up on posts. usually i do this with the posts out in the corners of the roof so i can remove the posts after i get the walls up to the level. Why i do this is I have built out in the rain-forest enough to know that no matter what I am going to be subject to the weather.

no this does not mean you need to make a box roof; it does mean the roof you put up for the building needs to be able to hold together by itself before it goes on. the other issue it the Roof needs to not leak. with those two criteria you basically make a boat that you put up on posts. IMO a roof that you cant turn over and float away on is a badly built roof.

This coarse sawdust is from the ripping blade of a circular saw. There's nothing dusty about it. Instead it is more like long thin chips. Dust from cross cutting is much finer and not elongated. This is a common waste product in the Cowichan Valley.

I could see using this either alone or as an additive to wood chip mixes. A mix made from this could be worked around frames and used as crack filler. 5 minutes on the phone should produce a lifetime supply. They generally deliver for free.
I'm shipping out 30 cubic yards of this material today.

Can I ask what size of home you are planning on building and if you have considered log construction. It is fast, 100% natural renewable materials and has far less waste than post and beam construction. The R value for most cedar ( the wood of choice in your area) would be between 1.25 R and 1.75 R per inch of log. That said an average log size of 12 inches would give you an R15 wall on the low side and an R21 on the high side. The difference with log is that it is also a very good thermal mass and once warmed it will radiate heat for days. Just a thought as you live in an area that quality logs would be readily available and if natural materials is your goal it just doesn't get much more natural than a hand crafted log home. If built in the proper style there is nothing but wood inside and out no artificial chinking or caulk is required and with the proper overhang you will not even require a stain on the exterior.

Ernie, LOVE the baseboard idea, thanks.

Jon, log homes are great, to be sure, but just not a style I like personally.

Dale, looking forward to seeing your project when it's up and running!

A cedar log home would be an extremely expensive option both in materials and labour. They use more wood than any other option and it must be good quality. Post and beam uses far less and since they are often covered with plaster or ?, they don't need to be attractive specimens. The materials for clay chip are mostly free and come from the waste stream. Good quality cedar has higher uses.

I gave away about 90 tons of scrap cedar this week. None of it would have worked in log construction but most could be used in clay chip. The skill level required for log construction is quite high and beyond what most of us are willing to learn.

Cedar has more taper than most other woods and would need to be partially squared to achieve any dimensional uniformity. Trimming of the taper would cause twisting in many specimens. There are a few builders of log homes here and they use fir and pine, probably because of the uniformity that can be achieved. Pine is cheap. The stumpage rate from crown land ie 5 cents per cubic meter for stands infected with pine beetle. They only effect the bark and cambium. I've never seen a log home of cedar. I've also never been in a good one, but have visited a few leaky, dark examples that require lots of supplimental heating. I demolished one which had twisty logs requiring flexible chinking. It went for farm use and for firewood.

Dale's recent posts revved up my thinking a little more about the idea that Andrew Parker had on using Cattail (which lead me to look at Tule) and Erica Wisner had on using woody plants with pithy centers, such as Elderberry.

A wall of Tule (Bulrush) in particular would have a great R value, in my opinion. For those not familiar with this plant, check out its cross section in the photo below of my Tule duck. It's like a natural minicell foam... with good memory retention (ie, when smashed, it rebounds to its former state...mostly). Another observation I've made is that it's always the last thing in the compost pile to decompose. I don't know why that is but it just adds to its attractiveness as a potential wall material. Cattail is slow to decompose in the compost as well....but I don't believe it would have the insulating properties of Tule. Good, yes....but not as good as Tule.

The downside with Tule would be availability. It's not a plant that grows every where and getting enough for a house might be challenging even in areas where it's found. Mixing in other materials would likely be necessary. If one had access to them, sunflower stalks would be superb. They're one of the pithiest plants I know of....the center like a natural expanded polystyrene (EPS), a highly insulative material. Elderberry shoots are similar in the middle but with less pith.

If I had more time, I'd experiment with a wall of Tule, Cattail, Sunflower and Elderberry. If needed, it could be fleshed out with straw. Another possible material to add in to the mix would be corn stalks. It's availability is higher than straw in some areas.

Just a little Sunday morning brainstorming....

This is an exciting thread here! I'm curious about the similarities and/or differences between a chip clay wall and a light clay-straw wall, especially as far as drying goes. I imagine the chip clay wall would tend to be heavier on the clay/cob then the light clay-straw, as the chips seems more as an aggregate and insulation, whereas the straw is insulation and fiber/strength. What would a typical ratio be for clay to wood chips? Is it similar to light clay-straw, in that you mix the chips with the clay and then place them in the forms, or is it more like chips being added to the clay/cob together as its put in the forms?

I like the idea of making wall sandwiches, mixing straw and cob in various vertical layers. I'm going to keep that in mind when I do my light clay-straw shop, putting 3 or 4 inches of heavier cobbish mix towards the inside. I remember when i was doing a workshop using light clay-straw, they talked about how easy it is to adjust the mixture, so you use the heavier, clayier mix on the south side, and the lighter more straw mix on the north.

Also, regarding electrical, the way i see it done is each box, be it switch or outlet, has a 3/4 inch pvc conduit running vertically up to the ceiling area. Simple and easy, and allows for rewiring in the future.

rhymeswithorange McCoy wrote:This is an exciting thread here! I'm curious about the similarities and/or differences between a chip clay wall and a light clay-straw wall, especially as far as drying goes. I imagine the chip clay wall would tend to be heavier on the clay/cob then the light clay-straw, as the chips seems more as an aggregate and insulation, whereas the straw is insulation and fiber/strength. What would a typical ratio be for clay to wood chips? Is it similar to light clay-straw, in that you mix the chips with the clay and then place them in the forms, or is it more like chips being added to the clay/cob together as its put in the forms?

I like the idea of making wall sandwiches, mixing straw and cob in various vertical layers. I'm going to keep that in mind when I do my light clay-straw shop, putting 3 or 4 inches of heavier cobbish mix towards the inside. I remember when i was doing a workshop using light clay-straw, they talked about how easy it is to adjust the mixture, so you use the heavier, clayier mix on the south side, and the lighter more straw mix on the north.

Also, regarding electrical, the way i see it done is each box, be it switch or outlet, has a 3/4 inch pvc conduit running vertically up to the ceiling area. Simple and easy, and allows for rewiring in the future.

Hi Rhymeswithorange,

I have yet to get firsthand experience with clay-straw. However, on my clay-chip project, I ended using 3 parts chips to 1 part clay slip. My slip was made from pure clay. As a mold inhibitor, I also added some Borax to the slip...roughly 1/2 cup per wheel barrel as I recall (I was mixing small wheel barrel sized batches at a time....by hand. Next time I'll use a cement mixer).

rusty

We are planning a project here at Sundog using the copious piles of pine and fir woodchips accumulated from two years of forest thinning. After watching many hempcrete videos we are doing test blocks using wood chips and lime. Anyone have experience with this? I am wondering about chip water lime ratios.