Cob House Project South America some tips needed!

Hello,

Im new on this Forum so excuse me if i ask anything thas has already been asked and answered!

I am planning on building my cob house in Suriname South America.
Right now i am still in the writing and planning phase and as i write more questions keep popping up.

Is there is anyone with knowledge of:

1. Putting in the floor after the stemwall: It would seen easier for me, the floor will take time to dry and you can work on the walls. Is this teh way or shoudl you place the floor in last?

2. Amazone, Tropical Climate: I will make the roof with overhngings so the walls will stay dry for the rain season. How ever, i wanted a flat roof... i guess this won't work, i'm scared that after long periods of rain my roof will be completely melted. Has anybody have some suggestiosn for me on this? Maybe cover the roof with aluminium plates?

3. Plastering: We have a special chalk here from calebashes. Can i use this for plastering? I would like to have my walls white. So i thought i would use this chalk as a final coat and treat them so it won't dust.
I also read about wheat flour paste. Is this to harden the wall and floor or can it aslo be used to make the colour of the cob whiter or lighter?


4. Niches and Cabinets: Do I freestyle these or should i build this around/over chicken fence or wooden planks?

5. Plumbing: I will use a regular flushing toilet so i will have some pipes etc. Can i just have them going in the floor and walls without the risk of them causing cracks in the cob?

6. Floor: I want an cob/earth floor, and i have set my eyes on this beautiful red sand. I've looked at some floor recipes and i think i get it but should i wait for teh last layer before sealing to add the mix with the red sand? Will this effect the solidness of the floor?
I want to seal the floor with lineseed oil and beeswax. How ever lineseed oil might be tricky since i would have to buy this and i want to uses products i can find in my surroundings. Does anybody know any other hardening sealing oils? ( coconuts, krape oil?? )


THIS IS THE WEBSITE ABOUT THE CALEBASH CLAY: http://www.moengominerals.com/en/power-pemba/metakaolien/
ITS CALLED PIMBA OR PEMBA..

Ok that's it for now lol,

Thank you in advance!

Hi Akua,

Good to see you're enthusiastic about cob, but a warning: cob is not necessarily the right material for a house in a humid tropical climate. You may end up with a house that is too hot and humid inside. Look at local housing methods that have stood the test of time; in many humid tropical areas these involve lightweight structures that allow the breezes to flow through...

The first rule of ecological building is to respond to the context.

Thank you for your response Robert.

I did consider the heath and found ways to keep the house cool.
Most houses here are from the colonial period and they are made from wood. Not all survived and wood is not really what i had in mind,
The people living in the interior have either cement houses by now or small wooden huts which they need to replace from time to time.

I looked at the clay we have, there is a company who sales this:

''PowerPemba Metakaolin is an admixture for cementitious materials such as concrete. Metakaolin is a high-reactivity pozzolan that increases the durability and strength of cement-based products. It is a fine off-white powder that is produced by heating refined kaolin (calcination). Unlike other pozzolans such as fly ash and silica fume, PowerPemba Metakaolin is not a by-product of an industrial process: it is produced as a pozzolan and therefore product quality and specifications can be strictly controlled.


Metakaolin enhances properties of Concrete
Concrete is a mixture of cement, coarse and fine aggregates (crushed stone, sand) and water. Through a chemical reaction of cement and water (hydration), the paste hardens and gains strength to bind each particle of sand and stone together into a rock-like mass. It is known that conventional concrete will deteriorate over time. Through the hydration a by-product called hydrated lime is produced. This hydrated lime has no binding power and makes up to 30% of the cement paste. Over time this hydrated lime is leached out of the concrete, leaving behind micro-channels, and thus weakening the concrete. Due to these micro-channels the concrete is vulnerable to outside influences like water, salt, chemicals, etc. This can lead to concrete corrosion.
Metakaolin gives the solution for this problem: With the proper replacement of cement by weight of approximately 20%, metakaolin has substantial benefits to concrete mixtures. It converts the hydrated lime into a stone-like material, therefore making the concrete denser and stronger. Metakaolin is the most reactive and therefore the strongest (and best) available pozzolan in the market. Metakaolin has been approved by the American Society for Testing and Materials (ASTM), the Canadian Standards Association (CSA) and the British Board of Agreement as an SCM (Supplementary Cementitious Material).''

I want to build with local available produtcs and this is something which is widely available (i think thats why they came up with the idea to mix it with cement)

It would be a more lighter substance and from what i hear it is very strong.


ANY advice is welcome!!

Akua,

1. The local Calabash Chalk has anyone used it as a building material?

2. Are you sure it's Calabash Chalk and what are the local builders saying about it's toxicity or emissivity?

3. Are there any manufactures of a CMU or Calabash Chalk concrete block?

4. Are local concrete suppliers using Calabash Chalk in their mixes?

5. Has anyone used the Metakaolin pozzolan in concrete or with Calabash Chalk? (what is stated about concrete above is accurate, not sure about Metakaolin pozzolan look for prove not sales claims) Give me a link to the company data?

6. What kind of earthquake activity is there? Worse case on a richter scale?

7. Are the local concrete builders using rebar at the foundation and/or flat roof-to-wall-ties or steel I-beams for earthquakes, it so what size and spacing.

8. What are your worst case daily temperature highs and lows and humidity levels during the year (BTW: Cob does better as it sees more heat and humidity through a process called enthalpy if designed right) .

9. How much wind driven rain (perhaps acidic) do you get? (this along with earthquake forces will be the biggest concerns).

10. Are you by the ocean(with acidic or salty wind driven rain) ?

11. Are you below sea level and how far below the building will a water table be? Does your building site drain well?

12. Does the government have building codes you must follow as in earthquake, wind, fire & smoke, etc) ?

http://www.moengominerals.com/en/winning-en-productie/fabrieksproces/

DISCLAIMER
All information herein contained is typical, accurate and factual to the best of our knowledge and we uphold stringent quality control procedures on our products.
However, no warranty is suggested or implied in respect of any recommendation, advice or suggestions made by any person associated to us, as the conditions, production, process and conditions of use are beyond our control.

Interesting,

1. Do you have access to crushed kaolin powder or small rock aggregates?

2. Can you buy AFK cheap or get a sample?

3. Is the Metakaolin cheap or can you get a small sample? Do you have access to a concrete ready mix or pure Portland cement or lime? Or Magnesium Oxide?

4. How expansive is the clay you have, how fast will it dry and shrink?

@ Tobias Ber Thank you for the reccomendation!

@ Terry Ruth,


Very interesting questions. I called the company today, andddd they are going out of buisness they stopped suplying to the main building stores. The reason for this is because the government doesnt support local companies. They would rather import than use their own natural recourses.
They only have a few bags left... 10 kg for about 65 American Dollars.

I can get my hands on the regular pemba ( calabash chalk), they sell this in almost any store or market. Some people eat it others use it for spritiual work what ever they do so much with it here. There are many mines getting this so thats why i was drawn to it... Its clay so i might be able to use it.

I stumbled on the website and im not that good with all de difficult words regarding to the process so thats why i called them. They explained that they would sell it eventually as a ready mix but also just the metakaolin. But they did not even het to that point.
When i told them my plans they were not sure if it would work without adding concrete.

Basically what i have is clay, sand, sharp sand and the pemba or metakaolin.



They told me a company was trying to make bricks out of it and they will bring me in contact with them.



About the building site... there is a lake... my backyard is right at it. No ocean no salty air... no acidic rain, no earthquakes.
We have some winds that can destroy houses but its mostly the poor contructions with not propperly installed roofs etc. The house i live in now is good and our roof never even moved during these winds. Its a regular type of roofing which they use here (aluminium /steel)


Right now we are in our small rain season.. today its 88 degrees farenheit wind 14 mph and humidity 62%.... its a rainy day...

On average, the temperatures are always high between 70 and 80 degrees.
A lot of rain (rainy season) falls in the months: January, February, March, April, May, June, July, August, October, November and December.
On average, the warmest month is October.
On average, the coolest month is January.
June is the wettest month.
September is the driest month.


I also did research before writing my plan about building with plastic bottle bricks. But an cob expert told me that it would be better to just use the cob without the bottles. Bottles can move and the cob might crack. Then i thought i will do the cob like that but what a bout the heat?? Found some sollutions but still i want to build my dream house.
The same expert told me you cannot cob over concrete.. it won't breathe. So i will not be able to do my cob furniture and niches etc.
Now i'm thinking plastic bottle bricks and cob with the pemba or metakaolin IF that will make it stronger and cooler?
I would still be able to cob my furniture i dont wnt to use a mix with concrete.

How ever have not met anyone who builds with either of them here so...

Well I think your biggest hurdle to over come is the toxicity of the Pemba, there are reports all over the internet it has over 5 times the lead content recommend for contact with bodily fluids. In a COB design if small particles become airborne there would be a health risk. It also has arsenic. We have a history with lead based paints causing all kinds of health issues. High heat and humidity usually exasperates the out-gasing.

I'd follow your experts advise on the bottle and not use them. Also, the Kaolin family of clays has a low shrink-swell or plasticity index so using it over concrete he/she is right would not allow it to breath or vapor dry. Other families of clay would breath.

Otherwise, if you answer my questions about your other clay type plasticity we can try and use it. Just need to know if you wet it about how much water will it hold and does it crack a lot when it dries? If it has a high plasticity we can use kaolin as a filler to take it down at the outer layers as a liquid water barrier since it seems as though you get some wind driven rain but not corrosive types, if you can source it somewhere cheap. AFK/MetaKaolin sounds expensive so if you can source some small rock aggregate, powder, or sand type cheap it may work.

Perhaps your best choice is to use the brick but if they are made of 100% Pemba you are still facing a health risk. They may come in handy at the lower walls to prevent erosion at a min.

Then i thought i will do the cob like that but what a bout the heat??

I'm not understanding your concern about COB and heat. It normally does well if the mix is right. Are you referring to Pemba does not take heat well?

not sure if you re on the right track here... it looks like things are getting more complicated than needed by the materials you re looking into.

you want a white finish for a cob wall that will offer some rain projection (as an extra, i suppose that would be a good idea). what about using lime/white-wash? what about a fine coat of lime-plaster? what about mixing lime-paint, there must be natural recepies online.

to my mind that would be simple and lime should be available.

@ Tobias Ber you are absolutely right.. it all seems so easy but as you actually get going obstacles occur.

I've heard from several people that a cob house in this climate would get too hot. At first i didnt see a too big of a problem but i keep hearing this thats why i have a heath concern.

The toxins in Pemba are real, although you have people eating it and using it on their face and body etc.
I guess i can use something else for the white colour i just figured it is locally and easy available. I am not sure about lime i would have to buy this just like the metakaolin.

I have 2 options right now... either go with my original plan and go for an all cob house. Climate and rainfall can be handled with the right knowledge.
OR use the plastic bottle method fill them with sand and mortar with cob. There are building done this way in many areas here in south america by mr Andreas Froese.

If i would go for cob i would use the location of the windows, overhangings, ventilation holes and the colour and shape of the roof to minimize the amount of heat that would stay in the house.
I would go for an earth floor aswell. Maybe the thickess of the walls might play a role of how hot it wiould get inside too.


If i would go for plastic bottles and cob i can also be able to do my cob furniture but the house from what i hear would be less hot inside.

Right now the more i research the more obstacles and questions rise so maybe i should just stick with my original plan. I will get back to you on the clay when i finished the tests. Are you suggesting that kaolin can be used to water proof the walls?
What are other ways to do this?
And i read about wheat flour paste, what exactly it the purpose? To strenghten or is it just to prevent dusting? I would use lineseed and beeswax on the floor to prevent scracthes and dusting.

Earth or mass construction can work in just about any climate, it works best in hot & humid. Any house made out of anything can over heat if designed wrong. We have a lot in hot( 110F, 44 C) climates around your average humidity or less. It all depends on knowledge. I'm speculating now with more info your native soils are low plasticity and if anything we need more pure expansive clay or vapor holding capacity, not lime. In addition to the wetting test above, put some in a jar add some water let it settle take and pic and post. If your clay is right and you can source kaoline as I described above, and straw, we could get there. Yes we'd move more kaolin to the outer stucco/layers as water proofing. The inner walls would be more clay to produce what is called latent heat of evaporation ( the walls dehumidify/dry/cool) and natural cooling. How effective that is will depend on your knowledge of windows and glass or SHGC, U-Factors, solar and wind orientation, natural ventilation, shading, etc. I'd need to write a book here

The leaching & microbial toxicity of most plastics in soil can be higher than Pemba might as well use it.

On average, the temperatures are always high between 70 and 80 degrees.
A lot of rain (rainy season) falls in the months: January, February, March, April, May, June, July, August, October, November and December.
On average, the warmest month is October.
On average, the coolest month is January.
June is the wettest month.
September is the driest month.

What are your average night time lows and day time highs throughout the year, how low below the desired set point you are comfortable at night sleeping to where you will need heat say in January, or how hot will it get in October in the shade with an average breeze in a house before you need a/c?? Do your humidity levels drop significantly at night in most of the rainy months especially june?

Terry Ruth thank you so much!
haha you SHOULD write a book lol


The average day time temp is around 85 degrees farenheit. At night it will drop to 70 ( and that would be the coldest) .
The house i'm in now has a nice flow of air due to where the windows are. I never get uncomfortable to the point where i would have to look for a heat source at night i don't even sleep with a blanket and we also don't have and AC or use electric fans.
When it gets hot and dry in august and september we might turn the electric fan on occasionally but thats when the heat goes up to 110 degrees farenheit.
The humidity at night during the rainy season would be 94% at night and during the day 70%
I personally adapt quite well to the heat and sun but thats me...

I previously stated that the temps are between 70 and 80 degrees but this should be 70 and 90!!


Actually my only worry right now is the heat and rain ... i can get a sollution for any other problem but if i build a house with so much work and effort and it turns out to be an oven or melts when it rains i would be really frustrated to say the least.

Bahareque (wattle and daub, among many names) is very prevalent in Latin America as well as many other parts of the world (Japan being one that does it well). It can be done poorly and poorly maintained or it can be a bank building or a palace. You decide.

Bahareque can be made solid or hollow. Solid is like traditional wattle and daub. It is thick cob held in place with a heavy lath of saplings, reeds or bamboo. Hollow uses an outer and inner lath that are covered in plaster (clay or cement). Solid can also have lath on the outside and inside with a cob/adobe core (there is another name for that particular configuration in Mexico, but it escapes me). If you have access to rice husks, the hollow space can be filled to make an insulated wall (you can also fill the attic with them). Walls would need to be made deeper, at least one foot, to give good insulative value with rice husks.

Split bamboo panels are used in Ecuador and Colombia as lath (reeds, wood lath or saplings are also used in the sierra). On the coast, the panels are often left bare to let the breeze through, but it is a fire hazard. People will often stucco the panels with cement. They are then difficult to distinguish from conventional concrete and masonry homes.

In the campo on the coast, homes are often built with concrete and block first floors, used for animals and storage, topped with a bamboo sided second floor living area, with a deep balcony on at least one side. Roofing is thatch (usually palm on the coast and grass or reed in the sierra), metal, or fiber-cement or clay tile. Traditional construction simply puts the house on stilts to raise it above seasonal or occasional floods. Many old hacienda homes were finished with stucco but had large windows and doorways with louvered doors and shutters. They were very stately when they were maintained, and very comfortable.

In the southern US, homes were often built of thick masonry and surrounded by deep porches to keep the sun from heating the masonry. Interior rooms had high ceilings, 10 to 14 feet (3 to 4 meters, more or less) and roof vents. The Cajuns in Louisiana sometimes used bousillage, which is a wattle and daub technique brought from France. They used retted Spanish moss as the fiber in their cob mix, a recipe borrowed from the native Americans there -- probably.

A flat roof will not work well. You want a steep two-layer roof, one to use as a rain screen and radiant barrier, then a large air gap, then an insulated layer (either insulated panel or an attic stuffed with insulation). Put a ridge vent on the outer roof and screened soffit vents to keep heat from building up in the gap. Also vent the interior space to the attic and put in vents through the roof or through gable vents. If the sun doesn't hit your walls, this arrangement ought to keep the house relatively comfortable. The interior roof could be natural materials, as it would be protected from the rain and sun.

One thing to be aware of in South America is that kissing bugs that inhabit cracked clay walls and thatched roofs, carry chagas disease. A thick thatched roof will keep you cool, but it must be fumigated regularly, or there must be some sort of sealed barrier between it and the living space, and clay walls MUST be maintained regularly and any cracks repaired immediately. Build it right and maintain it for good health and aesthetics.

Many years ago, I saw a beach house in Santa Helena, Ecuador. It was a masonry vault covered with a bamboo and palm thatch pole shed. Something similar could be done with bahareque. Maybe you could have your flat roof, but make it a covered rooftop terrace?

Terry Ruth thank you so much!
haha you SHOULD write a book lol

I’d need a lot of help on the writing part

The humidity at night during the rainy season would be 94% at night and during the day 70% I personally adapt quite well to the heat and sun but thats me... I previously stated that the temps are between 70 and 80 degrees but this should be 70 and 90!!

So, we have an average relative humidity(RH) exhaust from night times highs (eg: 94%) loaded interior mass drying to day time lows (eg: 70%) for humidity buffering. Temp intakes from day highs (eg: 84 F) drying wet walls from night during the day to night time lows (70F) to continue to dry the walls out, dehumidify, & cool. The ~ 25% is not bad but not great. Verifies COB can work here, or there is a dynamic mass benefit. 40% be great with a high plastic clay that did not crack.

With that high of a constant RH and heat you will need a lot of moisture and heat capacity out of the interior walls, floor, and ceiling. The biggest factor here is thermal bridging or more accurately thermal conductance or u-value in most parts of the world, inverse being r-value in some.

What are we talking about…a difference in temperature from the outdoor to the indoors and a distance that temperate has to go through the wall before it reaches the other side= U_Value.

Most studies show 2-4 “adequate as thermal heat and humidity sinks. In your case, since your annual temps are relatively high with no lows in the – 10F, but you’re always seeing high humidity levels an 8” wall would be minimum, 12” preferred. That is just to handle humidity and heat with no thermal bridging. You could go less but now you need a thermal break as in insulation in the center of wall or core.

In addition, not only is pemba toxic chalk is also high density high U-Factor so it would thermally bridge easy and need more thickness. Kaolin is the same. One reason they crack around bottles or plastics. This defines the need for a hygroscopic or high vapor holding materials like clay be added to the interior mix. Use the kaolin on the outer layers with some clay. Use less kaolin base mix on the interior. The white kaoline exterior would provide a natural reflective coating. If you want white interior walls uses a kaolin wash or wheat past, white earth or iron oxides, yes it is for dusting and durability there are some formulas on-line. Cost wise and structurally a monolithic design is best.

Add a lot of light reflective landscaping around the building. Use large overhangs or porches, trees, shading…..

Andrew beat me to it…..I call it a home within a home and it is the concept I use in all my designs. I love reading about these traditional techniques, putting them to practice another story. Two months ago I presented a flex home design as such made out natural materials. I was the only natural Architect there at the home show and a fellow from Ireland came up and asked if I have ever heard of thatch roofs. I said of course but, we have no skilled trades here. He said in Ireland the skill set is lost and even when it existed there were issues due to a lack of skill. If one spends a lot of time designing natural healthy buildings, fire and smoke spread is part of that. Our governments for the most part won’t allow it unless one can prove it is safe and that applies to all building materials. With as high of wind driven rain I would be careful here.

A flat roof can work but I’d be heading to a pitched w/dormers at least 8/12 and rain catchment, a cooling tower. Flat is going to put water loads and higher dead weight. You can design a home with in a home with any roof.

In high heat stack effect will be in full force so, the lower ceiling and smaller the building the higher the upper ceiling pressure to exhaust out vents and windows. Clearstory roofs with open windows would work. We are discussing gaps between the inner and outer building on this thread now: https://permies.com/t/54326/natural-building/Air-Sealing- Buildings. See my last post with the gap table. I use continuous vaulted gaps, no soffit vents. If you go the attic route make sure you research how to balance the vents.

Large gaps are not need. These gaps were tested but I’m challenging how to verify. 3/8-1/2 good any larger will reduce CFM/ACH. I’d test the mono design out before I went to plaster on double wyke walls, or, I’d look into those bricks and do a double wythe brick with a good r-value. In the hot humid SE US this has worked well for Clemson University and GA with air as core.

Windows if you can afford double pane, argon, low e, SHGC in the single digits or low teens.

HVAC: Ground air or water slinky or helix bore loops into interior walls and ceiling.

1.Putting in the floor after the stemwall: It would seen easier for me, the floor will take time to dry and you can work on the walls. Is this teh way or shoudl you place the floor in last?

Usually last after the roof and walls but before the windows and doors to dry in.

2.Amazone, Tropical Climate: I will make the roof with overhngings so the walls will stay dry for the rain season. How ever, i wanted a flat roof... i guess this won't work, i'm scared that after long periods of rain my roof will be completely melted. Has anybody have some suggestiosn for me on this? Maybe cover the roof with aluminium plates?

24-36" over hangs or wrap around porch. Flat roof can work depending on bearing wall spans. Done all the time in wet climates, details all over the internet. Keep it light and reflective. AL plates are heavy you will need a structures engineer to size the support beams, they also conduct heat you don’t want. U-value is high.

3.Plastering: We have a special chalk here from calebashes. Can i use this for plastering? I would like to have my walls white. So i thought i would use this chalk as a final coat and treat them so it won't dust. I also read about wheat flour paste. Is this to harden the wall and floor or can it aslo be used to make the colour of the cob whiter or lighter?

You can use pumba you know the risk. It may never be an issue, it can work on the outside of ventilation gaps with no tie to the indoors. Be careful it has a high u-value so you will need thicker mono walls or an isolative core that has to work with the roof and foundation structurally. Make sure the paste has high permeability and is not too dense. See above for more info.

4.Niches and Cabinets: Do I freestyle these or should i build this around/over chicken fence or wooden planks?

Best if tied to structure, but can be free floated in if not too wide. Use more dense mix underneath.

5.Plumbing: I will use a regular flushing toilet so i will have some pipes etc. Can i just have them going in the floor and walls without the risk of them causing cracks in the cob?

Best if in the floor. You may need to look at that thread and the radon discussion, vent stacks through walls.

6.Floor: I want an cob/earth floor, and i have set my eyes on this beautiful red sand. I've looked at some floor recipes and i think i get it but should i wait for teh last layer before sealing to add the mix with the red sand? Will this effect the solidness of the floor?

You can add find sand and pigment to the final layers, just make sure it is permeable but water resistant.

Hope that helps,

if i build a house with so much work and effort and it turns out to be an oven or melts when it rains i would be really frustrated to say the least.

Oh, and welcome to world of building design Takes a few new design builds to work out all the bugs and get the cost down for most pros. If you are that concerned stick with what is proven in the area and hire a pro. A good one is worth their weight in gold.