Author Topic: Cob/straw bale hybrid house  (Read 1753 times)

jpigg55

Re: Cob/straw bale hybrid house
« Reply #15 on: August 30, 2023, 07:23:40 AM »
Generally speaking, wood touching the ground isn't desirable here either due to rot and possible termite infestation. Where it's necessary, pressure treated wood is used.
The only place our construction has wood touching soil is the post frame posts. Mine are 6x6's made using pressure treated 2x6's to about 3 feet above the ground and white wood above that.
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

jpigg55

Re: Cob/straw bale hybrid house
« Reply #16 on: September 14, 2023, 07:44:36 PM »
We're at the slow process of mixing and applying the cob. It's a slow process, but actually going faster than I thought it would.
Due to the wall height, we're doing it in 2 phases. First from the ground up as high as we can comfortably reach. This phase is mostly done except for the area over the outside crawl space entrance. The upper portion has to be done from scaffolding slowing down the process. We've also started mudding the lower part of the interior walls when extra help is around.
Here's a picture of the south west corner with first cob layer applied. The small framed opening is for the wood cook stove exhaust pipe.
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

jpigg55

Re: Cob/straw bale hybrid house
« Reply #17 on: November 08, 2023, 07:06:05 PM »
A couple new pictures as the weather has warmed up between 15-25 degrees this week allowing for more cobbing.
We finished the outside first coat and are now working on the interior walls.
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

34_40

Re: Cob/straw bale hybrid house
« Reply #18 on: November 10, 2023, 06:47:47 AM »
I have only watched this type of construction on the TV.   I think it's fascinating!  Nice to see you are making progress. Keep up the good work - even if the temps have fallen  8-)
Clausing 108, Clausing 8520, Atlas Horizontal, Lincoln stick and mig welders

jpigg55

Re: Cob/straw bale hybrid house
« Reply #19 on: November 10, 2023, 11:59:48 AM »
I just wish I could figure a way to mechanically mix the cob. The only way we can get the moisture level correct and completely mixed to proper consistency and stickiness is to mix by hand. Not fun with 45 degree water and temperatures.
So far, I've tried using my backhoe, end-loader, and rototiller, as well as combinations of the 3, but it never comes out right. None of those methods work to completely break up the clumps/clods of clay either.
If I could find a way, I wouldn't care nearly as much what the temperature was.
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

RayH

Re: Cob/straw bale hybrid house
« Reply #20 on: November 10, 2023, 01:47:42 PM »
Just thinking out loud here:
Homogenize the a Clay-Sand-Water (CSW) in a conventional cement mixer.
Pour the CSW through a screen and screed to break up any clumps.
Put the CSW back into the cement mixer and add straw to suite.
Ray

Carpenter84

Re: Cob/straw bale hybrid house
« Reply #21 on: November 10, 2023, 03:58:44 PM »
Cement mixer, jimmy. 100%... Harbour freight, plugs into an extension cord.
Or any construction rent-all will have gas models.

https://www.harborfreight.com/1-14-cubic-ft-cement-mixer-61931.html
« Last Edit: November 10, 2023, 04:00:18 PM by Carpenter84 »
Shawn

jpigg55

Re: Cob/straw bale hybrid house
« Reply #22 on: November 10, 2023, 07:24:00 PM »
Guess I forgot to mention that method.
I have 2 cement mixers. One is the HF model Shawn suggested and the other is an engine powered mortar mixer.
Of the 2, the HF mixer worked best, but wasn't quite adequate along with small batches that take longer to mix than by hand.

The problem being that the consistency needs to be firm and sticky so it stays on the straw bales. It tends to stick to the mixer before it mixes completely making it a bear to get out. There's also the issue that the mix tends to go from too dry to just right, to too wet & sloppy with little change in water. Through trial and error, we found the best, fastest, and easiest way was mixing the cob mixture dry, loading it into a wheel barrow and/or my little Kubota tractor end loader. We then use 5 gal buckets of water to wet and mix it to the desired consistency by hand. If it's not right, it can be easily adjusted by adding more water or dragging in more dry cob mix.
Using the hand mix method in the tractor end loader works out great for the higher parts of the walls. We worked off of scaffolding and I could lift the bucket up to the perfect position to mix the cob and apply it to the upper portions of the walls instead of having to mix it and then bucket it up. That method is what we'll have to do for the upper portions of the interior walls, not looking forward to that.
PS
I wife shot some short videos of the construction and cob processes, but they load sideways on the computer and I don't have a software editing program to flip it or I'd post them too.
« Last Edit: November 10, 2023, 07:27:57 PM by jpigg55 »
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

Carpenter84

Re: Cob/straw bale hybrid house
« Reply #23 on: November 11, 2023, 08:13:12 AM »
Ahhh I gotcha. I understand now.

My only comment then is back in the day when I'd see the old plumbers mix the scratch coat dry bed for the shower pans (it was a sand mix that was near a dry consistency) they'd mix it flat on a sheet of plywood like an Italian makes pasta dough with the flour pond right on the countertop and wet ingredients in the middle and fold by hand.

Sounds like theres not much of a better solution for you. Hard work is hard.
Shawn

Carpenter84

Re: Cob/straw bale hybrid house
« Reply #24 on: November 11, 2023, 08:16:06 AM »
Did I read that the subsequent layers after the cob are actual parge or not? I don't remember.. a cement based parge mixes much nicer in a concrete mixer than the cob, by the sounds of it. So if that's the case at least there's light at the end of the tunnel of things getting easier...? Lol  :banghead:
Shawn

jpigg55

Re: Cob/straw bale hybrid house
« Reply #25 on: November 11, 2023, 09:54:16 AM »
The next layer(s) will still be a cob mix. The final layer may be either a coating of linseed oil or lime plaster, although we might not do either. Undecided as of yet, will do test on sample blocks to see how we like it.
Before this project started, we made a few test blocks with different ratios of clay to sand. This is done due to the variations in clay content of the soil from place to place. We’re using soil from the foundation excavation that is about 80% to 90% yellow clay. This determines the mixture that will be strongest and shrink the least when dry.
Unfortunately, we found the best mixture didn’t stick too well to the straw bales. To get around this, I added a higher concentration of clay to the mix which solved the stickiness issue, but results in cracks forming when dry much like the cracks you see in the ground during dry, drought conditions.
Subsequent layers stick much easier so the next layer we will go back to the higher sand content mix which will reduce shrinkage and cracking. The final layer will be a thin coat of a sand & clay mix that we will trowel on for a smooth finish.
BTW, another reason I decided not to use the cement mixer for cob was the engine on my mortar mixer broke. I think the rings went bad. Anyway, I need to use the HF mixer for mixing “Slip”, the mixture of clay and water that is sprayed on the bales using a spackle gun(https://www.harborfreight.com/air-tools-compressors/air-spray-guns/2-gallon-gravity-feed-texture-spray-gun-58614.html) to better bond the cob to them.  Using the same mixer for cob and slip would result in sand and straw plugging up the spackle gun slowing down the process to a crawl.
I did upload a video to my Google drive which appears to fix the horizontal  video issue, so here’s a link to it that shows the hand mixing an applying of the base layer of cob:
https://drive.google.com/file/d/1a-ZJeWLFPIpyVmTxIroov5GBN7UvTf0t/view?usp=sharing
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

RayH

Re: Cob/straw bale hybrid house
« Reply #26 on: November 11, 2023, 12:12:45 PM »
In the video, the cob looks more like a "dough" rather than plaster that I had in mind.
Is the video showing the typical process?
You hand mix a hand full and apply it by hand (no trowel)?
Incredibly labor intensive. It will be quite an accomplishment to get it all done.
Ray

Carpenter84

Re: Cob/straw bale hybrid house
« Reply #27 on: November 11, 2023, 03:18:13 PM »
Well, since someone’s not wearing shoes anyways, there’s always the smashed grapes method
https://youtube.com/clip/UgkxcPe3Na8YFmY04ZLwoq82N0zG-CAH2Af-?si=x1JiYO0lAVeLU-q0
Shawn

jpigg55

Re: Cob/straw bale hybrid house
« Reply #28 on: November 11, 2023, 04:47:57 PM »
Yes, a dough-ish texture is a close description. Too dry, it won't stick and too wet, it just slides off.
And yes, I seldom wear shoes when weather is warm enough. For anyone with a bad back, walking bare foot will help a ton. Makes you re-learn how to walk properly after a while.
You learn walking heel toe hurts your back instead of landing on the ball of your foot making your ankle work like a shock absorber. After 5 back surgeries with the final one being a spinal simulator implant, anything that helps is my motto. By summer I can walk on gravel with no problem. Only sucks when one catches a bee between the toes. LOL
Logan 6560H, SB 9A, Clausing 8520, Sanford MG 612

Carpenter84

Re: Cob/straw bale hybrid house
« Reply #29 on: November 11, 2023, 05:23:29 PM »
I bought a Peloton treadmill for my wife for Christmas 2 years ago (she wanted it... It wasn't an insult like buying your wife a vacuum cleaner... Lol). She had to learn how to run on the balls of her feet - like professional athletes do - it's weird to see, but it's absolutely the proper way to walk and run, much less impact - she has ankle problems.
Shawn