Soil Cement /Adobe Hydrid Slab for A Greenhouse?

Edit: Not sure if this is the right sub forum if not can a mod move it to the correct place?

I'm currently in the planning stage of building a greenhouse. Next year around March/April is the planed building date if all goes well if not then early May. So I'm mostly wanting to build as much thermal mass into the design of this greenhouse as possible because we do not have a southern exposure the greenhouse wont get direct sun light till about 9-10 am and receives filtered light from the trees for the last 4 hours of the day. Pouring a regular cement slab is not within our price range unfortunately although while researching adobe and other natural building methods that lead to finding soil cement. Soil cement is commonly mixed @ a 5-10 percent cement to soil ratio for heavy bearing parking lots and has been used the same way adobe bricks are for building houses in the south. It should not degrade over time and is waterproof which is important up here in Maine (zone 4).

Question

Does anyone have experience with soil cement or similar materials as thermal mass to keep their greenhouse warm (say 50* or better) all year with common subzero temperatures at night?

It would be awesome if we could warm the greenhouse all year without having to heat it with any kind of natural gas ect. If it does need to be heated I'd like to try and build a wood stove from soil cement blocks on top of the slab so it could transfer and radiate heat throughout the entire floor more easily having been made from the same material as the slab should make it easier to transfer the heat form the stove to the floor. Maybe a large rocket stove or something similar? The stove would have to be able to be left over night without stoking... any ideas?

Basically I'm at a total loss as far as heating goes the above is the result of brainstorming for a few days.

i have worked with soil cement, but not necessarily looking to it for thermal mass for a greenhouse. what i have found is you need a lot more cement to soil than many recipes call for. of course it depends on what the "soil" part is.....urbanite, broken smashed concrete, is also a good addition to this kind of mix and you can get it for free, though it requires some looking around and a lot of sweat to gather it.

i think your plan is sound, in my (unexpert but studied) opinion =)
sounds good.

an idea that i have had about heating in a cold climate is to do a bowl shaped design. basically digging out a large bowl in the ground and placing the hearth in the center of the area that would be underground. and there would be levels that rose up from there...

if the door was raised from ground level by some steps inside and out there would be less heat loss through it.
well just some thoughts, not sure if thats of help to you...doing something partially underground.

leila hamaya wrote:i have worked with soil cement, but not necessarily looking to it for thermal mass for a greenhouse. what i have found is you need a lot more cement to soil than many recipes call for. of course it depends on what the "soil" part is.....urbanite, broken smashed concrete, is also a good addition to this kind of mix and you can get it for free, though it requires some looking around and a lot of sweat to gather it.

i think your plan is sound, in my (unexpert but studied) opinion =)
sounds good.

an idea that i have had about heating in a cold climate is to do a bowl shaped design. basically digging out a large bowl in the ground and placing the hearth in the center of the area that would be underground. and there would be levels that rose up from there...

if the door was raised from ground level by some steps inside and out there would be less heat loss through it.
well just some thoughts, not sure if thats of help to you...doing something partially underground.

How far down would you dig? The frost level here is 4 1/2 feet down so can't really dig that far.

I have messed with soil cement. It is a good way to mud-proof a walking path. It doesn't change the mass over plain dirt.

I would rent a trencher and dig a trench around the perimeter and put down blue foam as deep as you can get. That will isolate the mass inside from the frozen ground.

I have seen youtubes with rocket heaters, barrel stoves, and cob ovens all used to warm a greenhouse. I would use the RMH or cob oven based on what you can get for wood to feed it.

R Scott wrote:I have messed with soil cement. It is a good way to mud-proof a walking path. It doesn't change the mass over plain dirt.

I would rent a trencher and dig a trench around the perimeter and put down blue foam as deep as you can get. That will isolate the mass inside from the frozen ground.

I have seen youtubes with rocket heaters, barrel stoves, and cob ovens all used to warm a greenhouse. I would use the RMH or cob oven based on what you can get for wood to feed it.

What is blue foam? Yes I have seen quite a few youtube videos about RMH's, Rocket stoves in general, and only one or two on cob ovens which are of interest as well. As far as fuel goes I've contacted a local lumber company to see if they will give away saw dust and wood chips which can then be compressed into logs/bricks for burning. Hopefully they say yes because the place is only a 5 min drive from home. Also have family members that can get free pallets from work. This is vary much a low budget building endeavor except the greenhouse itself that will be expensive it has to be to last the winters we have lol.

Basic blue or pink foamboard. No, it is not "green" but in the scheme of things it will do more good than harm as it will save you and the environment a lot in heating and emmissions from your stove. You could use lava rock, perlite, or any other recycled insulation--but you will get water conduction that a solid slab will prevent.

here is a link for the cob oven in a greenhouse: http://www.small-scale.net/yearofmud/2011/11/03/killer-wood-fired-pizza-oven-design/

A good cob oven is great for holding and releasing heat SLOWLY. You could fire it up at night and it will heat all night and be nice and warm in the morning still.

John Lint wrote:

How far down would you dig? The frost level here is 4 1/2 feet down so can't really dig that far.

well sorry i dont have any logistics for this, i am a wimp against the cold !

just what you got me thinking, by what you were describing.
...trying to find something to use as a thermal mass, and gather and buy stuff to do so....got me thinking if there was a way to instead use the earth itself as is...

never thought about that before...cant people who live in freezing places go underground?
i wouldve thought that was possible...but never considered the specifics....

R Scott wrote:Basic blue or pink foamboard. No, it is not "green" but in the scheme of things it will do more good than harm as it will save you and the environment a lot in heating and emmissions from your stove. You could use lava rock, perlite, or any other recycled insulation--but you will get water conduction that a solid slab will prevent.

here is a link for the cob oven in a greenhouse: http://www.small-scale.net/yearofmud/2011/11/03/killer-wood-fired-pizza-oven-design/

A good cob oven is great for holding and releasing heat SLOWLY. You could fire it up at night and it will heat all night and be nice and warm in the morning still.

Not everything in this build had to be 100% green so I'm totally ok with that. Dude that cob oven is freakin awesome! Although it probably would have been better to build some sort of rock/brick/something platform for it to sit on to avoid having to dig a hole to stand in but hey if it works it work right. OK so let me get this straight rough steps would be dig down under the frost level, fill the space with foam polystyrene ect, poor the soil cement slab on top, build the greenhouse, and finally build the cob oven. Sound about right? Might have to look into concrete posts instead probably would be cheaper since foam cost a lot if bought new... Heck this sparks some new ideas for sure.

Weird thing today Maine of all places had a 4.5 earthquake I'm located about 20 miles away from the heart of where it erupted from (not sure if that is the correct term or not) the house was shaking tv's nearly falling off the stands all I could think was I'm having a heart attack, the house is going to implode, or the hill is disintegrating and forming some kind of rock slide it was both my vary first earthquake and quite the fucked up experience...

I hate earthquakes. Zero warning. Even tornadoes have some warning--enough to put you on alert, anyway.

The footwell pit for the oven also will act as the cold well (per Oehler's design) so I would probably do it if I could.

Cob ovens are AWESOME!!! If I build another house, I am really tempted to use one as the "fireplace." RMH and cookstoves are more practical, but the way the fire dances in a cob oven is particularly mesmerizing--it dances in slow motion in the dome.

Here is a thread with more on insulating slabs: https://permies.com/t/10424/earthen-floor/Cold-climate-foundation-choices

The goal is to isolate the mass of your floor from the outside freeze line. You can put the insulation down or out (umbrella) to keep the floor and mass closer to the earth core temp.

R Scott wrote:I hate earthquakes. Zero warning. Even tornadoes have some warning--enough to put you on alert, anyway.

The footwell pit for the oven also will act as the cold well (per Oehler's design) so I would probably do it if I could.

Cob ovens are AWESOME!!! If I build another house, I am really tempted to use one as the "fireplace." RMH and cookstoves are more practical, but the way the fire dances in a cob oven is particularly mesmerizing--it dances in slow motion in the dome.

Here is a thread with more on insulating slabs: https://permies.com/t/10424/earthen-floor/Cold-climate-foundation-choices

The goal is to isolate the mass of your floor from the outside freeze line. You can put the insulation down or out (umbrella) to keep the floor and mass closer to the earth core temp.

Thanks for the thread haven't had achance to read it yet from the title though sound like it should be a major help.
All this is so confusing. Really I don't understand most of it other than the slab need to be protected from the frost heaves... Even worse is I tried talking to contractor friend to get a better understanding he couldn't even fathom houses being made from soil cement or cob.
I had been wanting to build a small test hut on the edge of the property next summer if there were a surefire way of weather proofing it. Snow is heavy and moisture sure would be an issue.
The greenhouse is the main concern though everything else is back burner for the moment.

Which would you say is more sturdy cob or soil cement? Do the two even compare? Is lime plaster even waterproof? I have actually done some googling on this stuff so it's not like I'm blindly asking beginner questions. (not insinuating anyone thought that either) From the literal hundreds of video's I've seen on cob and other natural building materials 99% if not 100% have been in a desert so trying to adapt things to a climate like we have is a bit different. For example cob alone wont cut it maybe a mixture of cob with cement added to the mix might.

Back to cob ovens for a moment. Have you seen this video? double chamber cob oven it has a chimney and an air intake why couldn't it be used as a fireplace with a ton thermal mass stacked around it? Maybe not as efficient as rocket stoves yet if you get a nice glass door for it then you've got a pretty damn stylish fireplace. Sure the exhaust is straight up instead of weaving through a bunch of cob like in the benches everyone makes. This would have the added benefit of doubling as an oven or rather doubling as a fireplace whichever way you look at it.

Any thoughts or considerations are greatly appreciated.

which is sturdier is a trick question, and why it is hard to get code-approved. It is highly dependent on the mix which is as individual as your soil--no universal recipe like concrete. Either can be strong enough, it depends on which is easier for you to build. For a floor I think soil cement handles moisture better, but that is just personal opinion.

Another non green idea... Could one make adobe or cob then coat the outer walls and/or parts in contact with the soil with liquid rubber? $40-50 at home depot gets a 5 gallon bucket of rubberized roof coating. One or two bucket normally does a entire trailer roof top so there would be enough to do a few coats all the way around a cob/adobe house depending how much surface area is being covered. One or two buckets max for the common one room cob featured on youtube most often. It's the stuff they use for the top of mobile homes to seal up any leaks in the roof. My only concern is sometimes on really hot days that stuff can stink pretty bad (if in direct sunlight) or at least the cheap stuff does. No one really likes the smell of burnt rubber lol but it just might work. Oh man so much thinking today my brain hurts.

Well, that is my non-green plan, at least for the earth contact parts. I will do limewash on the interior and above the splash line so it can still breathe, though.

R Scott wrote:Well, that is my non-green plan, at least for the earth contact parts. I will do limewash on the interior and above the splash line so it can still breathe, though.

Is a lime wash water proof?

You might consider stone slabs with cement grout. Stone has a higher thermal mass than soil. In Korea, prior to hoops houses ( and arguably better, in my opinion) they made their greenhouses with underfloor ondol heating, the flues being made of stone. Rocket mass greenhouses use the same idea. Here's a photo of one as they are still being used in North Korea. This one is earth bermed as well.





As for soil cement. I am anxiously awaiting geopolymer cement to get approved and have its mass production worked out. It chemically hardens earth to harder than cement and will be a much greener solution. There's a company in Oakland, Ca. which has major financial backing and it looks very promising!

John Lint wrote:

R Scott wrote:Well, that is my non-green plan, at least for the earth contact parts. I will do limewash on the interior and above the splash line so it can still breathe, though.

Is a lime wash water proof?

water resistant. If done correctly, it is about like goretex--it lets humidity in and out, but repels liquid water.

Suki Leith wrote:You might consider stone slabs with cement grout. Stone has a higher thermal mass than soil. In Korea, prior to hoops houses ( and arguably better, in my opinion) they made their greenhouses with underfloor ondol heating, the flues being made of stone. Rocket mass greenhouses use the same idea. Here's a photo of one as they are still being used in North Korea. This one is earth bermed as well.





As for soil cement. I am anxiously awaiting geopolymer cement to get approved and have its mass production worked out. It chemically hardens earth to harder than cement and will be a much greener solution. There's a company in Oakland, Ca. which has major financial backing and it looks very promising!

Really cool pictures Suki would totally love to have a greenhouse that big. Out of curiosity what is the climate in North Korea? The only thing about stone is I'd have to buy em' that or dig the entire yard up. Last year we dug a 10x50' garden area the yard is full of small and medium size rocks about as large as your hands folded together into a ball shape. It does sound like a good idea if a free source of largish rocks can be found. Do you happen to know the name of the company? Here's an awesome product for people in Aussi land
http://www.youtube.com/watch?v=eNO88AcJ60o

Edit: Embedded video

i have used polyurethane over soil cement before, only because thats what my friend wanted. i tried to talk them into linseed oil, and or beeswax - which is the more green alternatives for these issues(lime is a great idea too, a lime mix)
...but they had the polyurethane, and wanted that for whatever reasons (cheaper and quicker). and actually it was nice when it was done, all shiny and glittering, it has a nice visual effect and there was a lot of rocks in patterns that got beautiful in the shiny.

well, dont know i would recommend it exactly, but since you seem to be looking in non green direction anyway.
theres also some stuff for purchase in hardware stores.....that i have read the package and been tempted to buy it and try...i havent. but thats an idea, a possibility...they do make a commercial product which you add to regular cement that makes a waterproof cement....but its funky stuff ? like polyurethane...and etc

...and i dont know the long term fate of that little structure, but it seemed to work good in the short term when i was there.. here cob isnt that great, theres just way too much moisture. i wont say you cant do it, its just more to think about with the extreme moisture. if you are going to have a roof over it though...the cob should work ok with some moisture.

so thats why we started doing the soil cement mixes, which are always different depending on the need for it and the soil. i've made some floors, and even done soil cement for walls....really i would like to know how to make soil cement, WITHOUT the cement part....or any additives....but havent found how to do that. lime is probably the way to go with that....

btw i love that cob double sided oven, very cool, and the stone greenhouses =)
nice pics

Eh, I misspoke about soil cement.

I was thinking of the company Calera that is trying to make CO2 capturing cement pencil out.
I think that any of these geopolymer cements should one day be able to be mixed with local earth for a really really green concrete. Really hope they can make it commercially viable.

Korea's climate is much like upstate New York. Bitter cold in winter, very hot & muggy in summer, short springs & autumn.

And, those photos are not mine. They come from some missionary site: http://sfsdongdaewon.blogspot.kr/2010/02/reflections-on-nk-day-3-4-meeting.html
I've never been over the DMZ but live near enough to share the same weather.

ADDED: Oh yeah, and the stoves for these were either masonry or cob. Actually probably better than a RMH, since the cinders can continue to put off heat long after the flame has gone out.