For many, this is a repeat of a requested thread I'd posted on MG.
For those new here and those that come later with an interest, I'm re-posting the photos and what I recall of how it came to be.
For the new here that don't know, Cob is a mixture of clay soil, sand, and straw mixed together with water to a consistency similar to mud pies many of us remember making as kids.
Cob was used for making homes and other buildings in England and many other European countries as the materials were readily available and cheap or free. Many of these structures are standing and in use today despite being hundreds of years old.
The straw bale part is simply that, bales of straw, stacked brick style as exterior wall structure with the layers pinned together by driving lengths of rebar down through the bale layers. I bent lengths of 1/2" rebar into a 'C' shape to pin corner bales together with each leg of the 'C' being about 2' long.
The roof structure is a post frame, similar to a pole barn type pavilion. Ours consists of 3 distinct rings to facilitate having a wrap-around porch. The middle ring post (first installed) are site built 6x6 post build using 2x6 boards with pressure treated board on the bottom 6' that are set along the outside of the crawl space footings with a 2x10 ring header around the top for setting the roof trusses. These were measured and placed for a 9' wall height.
The inner most post frame ring are 4x4 posts made by nailing two 2x4's together that set on the concrete foundation top through holes cut in the floor sheeting. A top 2x10 top ring header was nailed to the top after butting them up against the roof truss bottoms. Additional 4x4 posts were built and set as door and window bucks.
The outer most post frame and ring header, also 6x6 and 2x10 materials, were set to add a 8' roof extension for the wrap-around porch, but with the ring header placed at 8' above the main floor level.
After these post frames and door & window bucks were in place, the straw bale stacking began. Early in the stacking process, I began to worry about the bales keeping stacked and straight from workers bumping into them or a nasty wind blowing up. My fix to this concern was to add 2x4's from the floor deck to the ring header and make and add more of the 'C' shaped rebar to the straight wall bale sections making sure to place them so I could wire from the rebar to the 2x4's. This proved to add a ton of stability and strength to the straw bale walls.
I almost forgot to talk about the foundation. We initially wanted to go with a walk-out basement, but the slope of the land, where we initially wanted to build, along with the available room wouldn't allow it. Where we moved the location, a walk-out basement wasn't a possibility so we opted for a crawl space. The hole was dug and the footings poured. For the walls, we opted to use ICF (insulated concrete forms) blocks.
We chose Nudura ICF blocks mainly because they were locally available. Fox Blocks were my first choice, but this was started during COVID and shipping was going to be outrageous and no local supplies available.
With no prior experience with ICF blocks, what I learned during the process about them, it turned out that Nudura was the better choice for me. If anyone is interested in why, let me know and I'll explain my reasoning.
Once the bales were stacked, an application of "Slip" is applied. Slip is a mixture of clay and water mixed to the consistency of syrup. It flows, but will coat your hand when dipped. The easiest way to apply this is using a Texture Spray Gun to spray it on the bales. This coats the straw and aids the adherence of the cob.
The last step is packing the cob onto the straw bale surfaces to the desired thickness, encapsulating them totally.
The cob/straw bale hybrid makes for an extremely well insulated house with the ICF blocks rated at R-40 and the walls estimated rating between R-40 to R-60 depending on how tight the bales were packed together when baled and whether stacked flat or on edge. The standard small bale being 4" wider than thick.
I'll post a few of the early pic's and keep adding until I catch up to current status.
More to come so feel free to ask any questions you have.
More pics.
And more pic's.
Still more. Tarps hung to keep driving rain off of straw bales until covered.
Satisfied, happy supervisor.
I need to take some newer pictures. Here's one from May of the North wall.
I realized something I forget to mention in the initial post. The "BIG" saying about a cob structure is "It needs a good hat and boots". The gist being you don't want contact with moisture or, at least, minimize it.
The Hat referring to the roof eave overhang. Recommended is 2' minimum. We opted for a wrap-around porch to almost eliminate rain from contacting the walls and because we really like wrap-around porch's.
The Boots referring to the foundation being a recommended 6" above round level and constructed to prevent moisture wicking up into the wall.
We had this point rammed home recently when we were hit with a huge downpour and high winds (tornado) in the 70+ mph range.
The only damage to the house was some of the cob being washed off 2 of the outer walls lower half by the horizontal rain.
This set us back as we had to re-apply cob to these areas.
This brings up another "lessons learned" point. Where the cob was washed away, there was a lot of surface sand loosely attached to these areas. The new cob didn't want to stick as the sand would coat the new mud and it would fall away.
We solved this issue by re-spraying a new coating of a thicker "Slip" and allowing it to partially dry before applying the cob.
This worked amazingly well and solved the issue.
To prevent this from happening again, when the final layer of cob is applied and dried, we will apply a coating of lime plaster
Lime plaster will seal the cob from the rain, but is still allowing moisture to wick out of the walls.
No new pictures since corn got too tall to get good views.
Interior walls got framed in, but really busy moving out everything from current house. Closing date approaching fast.
Trenched in the water line to the well yesterday. Went back today to back-fill, but ended up with a rescue mission.
More pics
Got him out. Wobbly legs, but okay.
Poor fella. Bet he was glad to get outta there in one piece!
Wow! Every once in a while you hear of such a story, but I'll bet you never expected to be a part of one!
Great job looking out for wildlife there!
Wow! That's amazing he made it!
We're finally to the last stage of applying lime plaster to the walls.
The picture shows the first application to about half way up the wall, far as I could reach from the ground. There will be 2 coats applied to finish it.
I ordered a stucco gun and found an engine powered air compressor on Facebook marketplace that's making this go much easier and faster than troweling it on.
Good to hear that it's going easier, that's always better IMHO :smiley_goodbye:
Had a rough night. The "Supervisor" went missing. Wife thought she'd heard him get into it with a wild critter and ran off chasing after it or worse.
Was out looking and calling half the night and back at it at first light this morning.
She finally found him this morning. Turns out he'd snuck into the barn and got shut in. Didn't make a sound until this morning.
Amazing how we get attached to our animals. Glad you found him.
Popped on to try and catch up with what's been happening. Thought I'd make a quick update on the house construction.
Delivery and contractor delays pushed recommencing construction until almost mid November.
We had to move in prematurely due to below freezing temperatures forced us out of the camper we were staying in.
Things are progressing slowly, but we have a working toilet and heat using a pellet stove. The final pieces of the hydronic heating system should arrive later this week or early next week, but will take some time to get it up and running.
I can now attest to the insulating value of the straw bales. We installed a metal ceiling and I currently only have a single 3.5" layer of mineral wool insulation until all the lights and electrical are done in the attic.
Our only heat source is a pellet stove rated at 49,500 BTU's, but is keeping the house above 67 degrees even with nighttime temperatures dropping down to the low teens with 25+ mph winds.
Construction still going, although snow and colder temps limiting it to interior work. Finally got enough of the laminent flooring down to allow getting some furniture.
Almost to the point of finishing what can be done until warmer temperatures allow exterior work. We came to the conclusion that some of the interior work will have to wait until Spring, but at least the house is becoming more liveable.
Well, you got lights, heat and tv... even the pup looks happy. :smiley_groot:
Taking shape and looking good, Jimmy!
I just took a closer look and noticed the picture hanging on the wall. Bravo, Jimmy!! :smiley_pig:
Quote from: TerryWerm on Jan 10, 2025, 07:16 PMI just took a closer look and noticed the picture hanging on the wall. Bravo, Jimmy!! :smiley_pig:
Thanks, birthday present to the wife from a close friend of hers.