Using hay for cob?

We just purchased 11 acres. It is an old pasture land that has been used as a hay field now. I've been reading books on cob and found that they recommend using straw instead of hay. The main thing i've saw is that they say hay decomposes...but so does straw. If I let the hay dry out before harvesting would it be fine to use? Maybe it is cheap enough it would be better to just buy it but I'd like to use everything I can from my property. Of course if we don't get out of this drought here in Texas I may not get much hay anyways.

Hello Nathan,

Here you go.....

Hay is grass, alfalfa, timothy, clover, etc. that cows eat. Straw is the stem left over after oats, wheat, barley, etc are harvested.
Wheat stems are hollow and have good tensile strength. Hay has seeds in it (like weed seeds). Straw is just the chaff and very few seeds.

Most of the cob books and experts have said we should not use hay for building with cob, rather than straw, but I'm completely at a loss about WHY. I've received all kinds of different answers.... "It will sprout" (so what)... "It's not as strong" (huh??)
For instance, in the Becky Bee book she says "Do not use hay. It decomposes." Yet a few sentences later she states, "If you're an ambitious purist, you can gather your own grass stalks or experiment with other plant fibers." Well, HELLO, what do you think hay is? Grass stalks. Not to mention, as an avid composter, I can tell you that "straw" decomposes just the same as "hay"... and "hay" can mean anything from brittle stalks with seed heads to thick straps of wide grass to bales of weeds and wild rose stalks and willow branches..
Can anyone give me a reason that makes sense to me why we shouldn't just use my neighbor's weedy hay for building with cob?

I think that generally, straw refers to the cellulose stalks of a grain plant, whereas hay can mean the leaves, stalks and seed heads of a green manure crop such as alfalfa, clover, bromegrass and the like.

Straw:
- No real food value
- Long, skinny fibers are convenient to work with
- Good tensile strength

Hay
- Lots of good eating there. As they say, hay is for horses.
- Prone to sprouting and rotting
- Probably a bit more difficult to work with, with all the plant parts present
- Possibly less tensile strength as it's not strictly stalks

When people say to avoid building with topsoil, I think it's a similar argument. Topsoil built up over eons is far too valuable to be used as a building material. Better to remove it for gardens and use the free-of-organic-matter subsoil for building.

I hope this helps explain it a bit ♥

There has never been straw available in my locale, as far as I've been able to determine....

Generally speaking, you want long fibrous material with low food value. We don't want to be building edible walls.
The difference between straw and hay is when it's cut. Hay is cut before the seed is finished, it's green and full of life. Straw is cut after the seed is set, the plant is dying back, the stalks are no longer green.

Now, I've seen cob made with straw that was FULL of seed.. After a couple days the walls looked like a Chia Pet, totally sprouted out.. A few weeks later, as the building dried out, the sprouts died and were easy to pull off the walls. There was no visible negative effect on the building.

Common wisdom says "don't do it", but what the heck, I say that you should try the hay.
Try it on a low risk situation, don't go building a house with it right off. Make some test samples, maybe a medium sized blob of cob, or even a small oven with the hay in it.
See what happens, give it some time, maybe do one next to it with straw. See what happens and let us know.

My bet is that the food value in the hay will attract insects, mold internally or maybe color-bleed through the layers.
Won't know for sure till it's tried.

Hey Nathan, Just thought I'd add to this discussion. My grandfather Erwin Peik use to milk cows at his farm in Minnesota. Had a silo and corn meal mix for fodder for the cows. But he also owned (which I own now) 12 acres of bottom ground that is covered with reed canary grass. Where as now it is "hayed" for winter fodder for cattle, then it was left on the ground to bleach out in the sun and become straw for bedding in the barn for the cows. The "hay" had a blonde color to it just as the straw coming from harvested wheat fields in this area. After being bleached out I really don't think it had any fodder value to it. I think the measure here is if you cut it on a regular basis, it tends to be more leafy and green for consumption. But when you let it grow out for most of the season it will become more stem filled than leafy. Stems being hollow add more roughage to the cob than thin leafy matter. Dan

For what it's worth I am pretty sure the author of Serious Straw Bale lives in a house made of hay bales. I had some straw sprout in my plaster and it was easy to pick and died off fairly quickly. So the hay provides the long fibers for strength and if any seeds do sprout they ought to die off fairly quickly.

I say go for it!

Hello Mr. Rigg,

I would answer that Ms. McBride 's answer is more correct , as that Hay is for animal feed. Also, Hay can spontaneously combust , thus - I would NEVER BUILD - with hay bales – nor would I build with Straw bales except for emergency construction situations. I might would also say, don’t build with cob either , go ahead and build a proper wall by ramming the building soil in place . Rammed Earth ( a higher form of Cob ) makes for much safer and longer lasting walls!

Additionally, If your lucky enough to have a quality Hay Field, If your not feeding it to your live stock, you might should be selling it and buying Wheatstraw as that even just good quality Hay, brings a pretty penny .

Best Wishes & Happy Building !

Joe Woodall, Rogue Eco-Architect
Georgia Adobe

Georgia Adobe wrote:Hello Mr. Rigg,

I would answer that Ms. McBride 's answer is more correct , as that Hay is for animal feed. Also, Hay can spontaneously combust , thus - I would NEVER BUILD - with hay bales – nor would I build with Straw bales except for emergency construction situations. I might would also say, don’t build with cob either , go ahead and build a proper wall by ramming the building soil in place . Rammed Earth ( a higher form of Cob ) makes for much safer and longer lasting walls!

Additionally, If your lucky enough to have a quality Hay Field, If your not feeding it to your live stock, you might should be selling it and buying Wheatstraw as that even just good quality Hay, brings a pretty penny .

Best Wishes & Happy Building !

Joe Woodall, Rogue Eco-Architect
Georgia Adobe

Well I can agree that hay is usually used for animal feed and in your neck of the woods hay may bring a pretty penny but here in VT hay is one half or even less the cost of straw. Also, as far as spontaneous combustion goes, moisture is key, "over 22% increases the risk." so as long as your hay bales are below that you'd be safe. And if your using the hay in a cob mix then it won't matter at all as it will only combust in large bales or piles, not as individual pieces. That is why it is best practice to have a moisture meter when you buy your bales and for monitoring them once the structure is built.
http://www.wa-hay.org/publications/Spontaneous%20Combustion%20in%20Hay%20Stacks.pdf

As far as straw bale goes, I wouldn't trade mine for the world. It heats with 1 - 1 1/2 cords for a Vermont winter, needs no a/c in the summer and moisture levels are 10 - 11%.

Mr. Woodall, in your opinion, would rammed earth work in a cold climate? I suppose once the walls are heated it would be only a matter of maintaining that heat, no?

cheers!

Hi Mr. Viglas,

Yes, Rammed Earth is a very fine choice for cold climates too & it‘s always my first choice of building materials – just so long as it's properly insulated R/E, . Also Earth Sheltered structures fair better in the long haul in all climates too.

Static temperatures of our planet then can be maintained in the structure, at about the Earth's static norm in north America ( of 58 degrees +/- with elevation & location changes effecting this somewhat ) all year round and then temperatures only have to be augmented slightly, by the residents ( heated or cooled ) through solar gains & losses & a wood stove perhaps. Add the proper ventilation to your mix , and you have the perfect structural combinations, & a building that can be ventilated properly. too

For example in a Insulated Rammed Earth Building, one could open the South facing sky vents & draw in fresh North Air streaming through Earth Tubes 3+ feet in the ground. Do this all day from the main sun point of the day say 9 AM on in most of the Winter and never over heat from solar gains , then close up the structures vents , just as the sun starts to fall ( 3– 5 PM ) and the temperatures inside will return back to the thermal mass’s static temperature in about 30 minutes. Do this in a Strawbale house & you may be heating a bit more than your original number showed.

Now, in a R/E building It does take about 28 days to set the thermal mass temperature of say , a 24”+ thick wall with a heating charge to its heated charge and the your wall will loose that heat completely , within a week or even less if its not recharged often , but the amount of actual heat required to be supplemented into the structure , is very minimal, due to the flywheel effect of thermal mass & solar gain working in your favor .

I.M.H.O. , With Strawbale you only get, a well insulated structure, subject to potential moisture failure or at least some problems , perhaps caused by if for no other reason, than the living conditions of “normal life“ ; and not a structure that can be ventilated enough ( without gaining moisture ) , to dissipate what's in & on its walls. Interior moisture may never stay out of the interior of those walls, without having to dry the building through heat & some type of supplemental ventilation system within that Strawbalewall. That straw will breath and this is where the problems have come from ( normally ) .


The studies on Strawbale walls that I’ve been read, showed me that the moisture threats to the durability of the stucco & Strawbale sandwich wall, finds that both Straw and Wood equally will rot, if the wall moisture rises to 12%+. At your 11% your on the edge of danger. The plastered Strawbale house construction, does offer inexpensive & well insulated long successful performance records - but I have only read about them being only under rather ideal conditions. For Example I recall reading about those 100+ year old structures, out on the dry plains of Nebraska.

My experience with wood frame constructions, as well has lead me to never use any more wood fiber or any material than I must; and all other cellulose fiber materials have proven time and again that the accumulation and retention of excessive moisture, can & will degrade their performance, quickly rendering them unserviceable ( even cellulose insulation which is one of my favorites too ) . Thus , as I said, I always choose 1st, All Masonry Homes - Built Mostly Of Properly Insulated & Moisture Proofed Rammed Earth + up to 80% recycled materials .

I hope that was “constructive” to the discussion & Best Wishes to you up in lovely VT !

Joe Woodall, Rogue Eco-Architect
Georgia Adobe

Thus , as I said, I always choose 1st, All Masonry Homes - Built Mostly Of Properly Insulated & Moisture Proofed Rammed Earth + up to 80% recycled materials .

This leaves me wondering.... What do you use for proper insulation? And moisture proofing? Of rammed earth.....

Hello Ms. McBride,

At Georgia Adobe, we design our walls to be wrapped & insulated, so they can be kept dry from outside moisture, thus they will hold the planed temperatures longer.

When Georgia Adobe's are designed at their top performance level , we specify 6" of 4 pound strength polyisocyanurate foam insulation , to be placed as sheets or sprayed in place all around the outside of the optimal 6 feet total, thermal mass walls ( also under the floors as well & above the masonry roofing materials, should that Georgia Adobe Home be Earth filled on top ) and then we add an EPDM pond liner to totally wrap the entire structure ( all sides ) , with an additional 2" foam sheeting and a double 6 mill poly, outside that completely surrounding all elements, just to protect that EPDM liner. This is to protect the EPDM water seals, from roots, stones, etc. growing , or falling in during , normal back-filling and compaction against the exterior , Earth sheltered section .

Best Regards,

Joe Woodall, Rogue Eco-Architect
Georgia Adobe

Hay as a definition for building materials is meaningless. High protein feeds such as alfalfa, clover mixes, legumes, and other green materials do pose a risk of rotting very rapidly, potentially decaying before the wall dries. However, decay is generally a related to not just water but also air.

Grass hay types should perform very well in cob walls. I do not have any longterm data, but I have used grass hay in some of my projects (ag builings) with no immediate issues. The reed canarygrass dried in the sun is a great example of a material that will work just fine - think along the lines of composting, greens and browns. Carbon dominant materials should work just fine in a wall. Per unit of volume and of mass, grass hay will generally have far more fibers than straw with excellent strength.

Several of the original Nebraska structures were made from hay, not straw, and many survived for over 60 years with no maintenance and often no roof.

Cob is a very versatile material, and does far more than just build exterior walls - everything inside a home can be made from it as well. Mr. Woodall's system sounds exceptionally high quality from any standard, but just the cost of 6" of foam sprayed or laid around a home would exceed the total cost of many cost conscious cob structures. And, in an earth shelter situation with a large, counterlapped pond liner, why not just extend it 20' past the home and use standard passive solar dry-earth six month flywheel effect to create a permanent stabilized temp?

Adding to your comments Matt, I would say that the most important, intended feature, in 'Natural' construction is breathe-ability. Naturally allowing moisture to escape. Assuming no huge amounts of water, such as in a flood, penetrate then air flow will suffice to eliminate moisture. One exception is in bathrooms or other places that receive a lot of steam. For these you want a vent, just to be on the safe side.

However, you start adding any impermeable materials and you'll run the risk of trapping moisture and then rot will soon follow. Unless, as Joe indicates you completely surround your walls.

I have to say that Joe's methods sound like a hybrid/compromise between natural and modern man made materials.

Myself I would not use foam against earth in any situation I can think of. My exceptions would be making a homebuilt cooler with sprayfoam - very efficient. A local peach and plum guy brings his stock from colorado and georgia up here to south dakota in a 1/2 ton with topper, interior of topper sprayfoamed with bubble foil baffles, inverter, mini ac into custom slide out, coolbot. I would also consider foam as a great way to insulate and utilize a grainbin for a home or shop, but in that situation (interior foam spray and then stucco inside a reclaimed bin) a whole house air exchange system would be desirable in my climate.

I think that there are even many other potential odd materials that will make good cob. Yak hair, yucca fiber, lambsquarter fiber, long strip pounded bark (oak?), palm leaves, canes or reeds, and pretty much any other fiber if you were somehow in a survival or extreme remote situation (jungle, mongolian foothills, pacific island?). A material I have used was whole entire western red cedars stacked above a no-straw cob mix, laid on gravel substrate. Stacked more cob on top of the brush. Ag building so why not try it. Maybe after a while I will dig it up with the skidder and see what transpired (they were still a bit, um, green).

Oops maybe I should have said, functional cob, not good cob. But why not experiment? Lambswool? seems too oily but... Oh, how about barber shop trimmings - easy to get some places, and human hair is really strong.

Nathan Rigg wrote:We just purchased 11 acres.  It is an old pasture land that has been used as a hay field now.  I've been reading books on cob and found that they recommend using straw instead of hay.  The main thing i've saw is that they say hay decomposes...but so does straw.  If I let the hay dry out before harvesting would it be fine to use?  Maybe it is cheap enough it would be better to just buy it but I'd like to use everything I can from my property.  Of course if we don't get out of this drought here in Texas I may not get much hay anyways.  

Hi all,

So, Mr Rigg, did you finally try it?
Coming from eastern Canada, we are in a season where there are no straw available right now. I was therefore interested in knowing if you tried the hay and how did it go!

Thanks!

Colin

I doubt he's still around since it's such an old thread. FWIW, I have used hay for cob. All the ranchers in my valley grow hay and I would have to drive 2 hours each way to get straw. A neighbor gave me a bunch of hay bales because they had some mold in them, mostly on the bottoms. I opened the bales and put the moldy parts in the compost heap and used the rest for my cob. All the books tell you not to do this but it worked out fine for me. I did have some sprouting but the sprouts just withered and died as the wall dried out. If I had convenient access to straw, I would have used it but I didn't. I do live in a very dry climate so that helped. It worked out so well that I plan on using spoiled bales again. Just my experience, YMMV...

I'm planning on using some bits of hay on a round bale that has been sitting in the weather since the spring. Basically just the cellulose and not the starch is left on this hay, and I will be careful to just get the yellow bits that are on the outside, nothing that looks like hay that could still rot. I'm going to be building a cob oven so won't need too much. I'm sure wild plants would have some fibrous bits that could be used for the binder in the cob. Another option I thought of recently is the old twine off bales of hay, chopped up so it doesn't tangle up too much. Sisal twine would be best, but I think the plastic would also work, but not too close to the hot part of a cob oven. Some hay is wrapped with netting, and this also could be chopped up and used for cob I imagine. Any beef farm that feeds hay would have quite a few pounds of twine that they likely throw out.

I'm pretty sure there are some plants that grow near roadways around here that could be used for cob. Hopefully I can get some pictures.