Using cement as a rock dust.

Discussion in 'Planting, growing, nurturing Plants' started by FintanK, Jan 16, 2011.

  1. FintanK

    FintanK Junior Member

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    This may seem like a very naive question. Has anyone ever considered applying cement dust to their garden in the same way they apply rock dust?
     
  2. DonHansford

    DonHansford Junior Member

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    Aaaah, in a word.... NO!

    Cement is not "rock dust", like "crusher dust" is (by-product of screening/crushing blue-metal (basalt) to fine construction grades). Cement is a "hydraulic" extract from ancient coral reefs.
    Hydraulic cements (e.g., Portland cement) harden because of hydration chemical reactions that occur independently of the mixture's water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not water-soluble (or plant-soluble).

    This means, basically, that anywhere you put cement dust, will become as "hard as concrete" - not the best growing medium!!

    Incidentally, Portland cement powder should not be used in conact with anything that is porous, due to it's hygrophobic tendencies. Funny how modern building techniques use cement to bind bricks (porous) or Besser blocks (porous) or pavers (porous), and become completely unsustainable as a result! - (Sorry, personal hobby horse came out for a short gallop there!).

    Although cement is made up of a number of beneficial minerals, the specific combination makes them rather useless as a soil additive for gardeners.

    Pre - World War Two, the great majority of civil construction projects using some form of stabilised earth, used lime (in a few different treated forms). All of those products can be re-used or recycled, but you cannot recover bricks for re-use that have been mortared with cement-based pozzolans. Virtually every clay brick that has been made since 1950, will go to landfill once it's primary structure is no longer wanted, compared to over 80% of the clay bricks made by mankind before 1950 being recycled up to 4 times!

    Plus, lime actually absorbs carbon dioxide as it sets - virtually as a 1:1 ratio of what it took to refine itself - concrete (the end product of cement + aggregate + water) does not re-absorb any C02 during the hardening phase.

    Promoting the use of Portland cement for anything, is not going to put you in my good books!

    Welcome to the forum (hopefully without cement dust on yer boots!) :)
     
  3. sun burn

    sun burn Junior Member

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    You better not come to my place then Don, we'd fight over the Portland cement, cause i don't know what else to use. I can't use the earth here, its full of tree roots now. And I don't want big holes all over my garden. I know PC is not a great thing for the environment but it all looks pretty bad whatever you use in one way or another. And if it is ok for the environment such as plantation timber, then i can't afford it.

    I want to point out that the amount of concrete materials in my FC mix is a lot less than most concrete jobs. The planks will not be 4 inches thick like most concrete but less than one inch, according to the guys on the forum where i am trying ot learn about this stuff. So that means a helluva lot less materials. That said, the mortar mix is going to be 1:1 so while I will use less sand and aggregates I may not use less cement though i haven't done the calculations yet.

    Can you elaborate on this quote. Explain it please cause its not clear what wrong with it. Do you mean hyDrophobic? if not what is hyGrophobic? But what is the problem that is caused in using cement with bricks, besser blocks, and pavers. How do you mean something becomes unsusitainable.

     
  4. gardenlen

    gardenlen Group for banned users

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    don't know how much old coral reef gets used anymore? dredging operations in moreton bay have been stopped a long time ago, on environmental reasons, and rightly so.

    fly ash is now used in cement not sure if it replaces the coral?? but on that alone i wouldn't be using cement in my garden, won't ever consider buying a cemet tank either.

    i'd buy the rock dust for sure, up gympie way there is a bloke up near the sales yards somewhere who will mix the rock dust to suit your soil (as per soil test), even better, as far as i know it is not that expensive.

    len
     
  5. DonHansford

    DonHansford Junior Member

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    Roman roads still being used after 2000 plus years - most of the roadbase for those is stabilised with lime. Golden Gate bridge - footings were lime-based concrete. St Pauls cathedral - all the mortar joints are lime. 500 year old pub in Devon, England (one of the wettest areas around) has cob walls, coated with lime plaster, and a thatched roof. Millions of homes around the world are built with, and protected by, lime - not cement.

    HyDrophobic means it hates, or repels, water - HyGrophobic means it will draw moisture from the air (humidity) - that's why an opened bag of cement will harden, even if it is left in a shed out of the weather. Once that happens, you cannot re-constitute it by crushing it, and mixing it with new concrete,because it has used up some components in the chemical reaction and will therefore weaken the new mix. Lime mortar can be crushed, and mixed in with new plaster for 100% re-use.

    The use of cement mortar in brickwork means that the mortar is so firmly attached to the porous surface of the brick/paver that you cannot clean the mortar off to re-use the brick, without damaging the bricks beyond repair. A couple of blows with a hammer will remove lime mortar (which can then be crushed and re-used).
     
  6. sun burn

    sun burn Junior Member

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    What is wrong with flyash len?...( grumble, why do people never explain themselves. grumble grumble. ;-))

    Don I will look further into the possibilty of using lime where i can but my first questions is, if lime is so good why did people switch to using cement? Are you certain all those buildings have not experienced major repairs at some point in their history, maybe even radical rebuilding.
     
  7. gardenlen

    gardenlen Group for banned users

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    g'day sun burn,

    you can do some research on it, it is full of nasties as it has been explained to me i can't remember all but one is low grade radiation material, the other reason i would never use cement as i said in teh last post is teh gov' are using cement to hide the fly ash in so they don't need to dispose of it in other manners, same as mediuam grade and low grade industrial waste the low grade goesn into the sewer, and the humus from the sewer as well as the medium grade (what ever that means their rules) end up in garden improvers and all potting mixes etc.,.

    and why even consider using cement powder (which most would have to buy) when that bloke up gympie way sells crushed rock mix for probably about the same price?

    len
     
  8. sun burn

    sun burn Junior Member

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    https://enr.construction.com/opinions/editorials/2010/0414-FlyAshDilemma.asp when i ask on google what is wrong with flyash, most of the results that came up on page 1 don't look informative. But this one looked the best. Upon reading it, i am not clear that it is a danger.


    On asking google what is flyash, i got this answer. It doesn't answer the question what is wrong with flyash.
    How hard it is to explain yourself len. What is wrong with flyash is a basic question which you could and I believe should have answered in your post since you seem to know what the problem is and your statement is provocative. HOnestly i despair of the net as a communication tool. People are so vague as to be utterly unhelpful more than half the time.

    it seems to me that a) the government is not hiding flyash. When you buy cement with flyash it is identified this is partly because flyash has useful qualities in making concrete like slowing down the curing process. and b) if flyash is in concrete it is stable and fixed is it not. As indicated by the link i just posted above.
     
  9. DonHansford

    DonHansford Junior Member

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    Fly ash closely resembles volcanic ashes used in production of the earliest known hydraulic cements about 2,300 years ago. Those cements were made near the small Italian town of Pozzuoli - which later gave its name to the term "pozzolan."

    It transformed the possibilities for making concrete structures, although it took the Romans some time to discover its full potential. Typically it was mixed two-to-one with lime just prior to mixing with water. The Roman port at Cosa was built of Pozzolana that was poured underwater, apparently using a long tube to carefully lay it up without allowing sea water to mix with it. The three piers are still visible today, with the underwater portions in generally excellent condition even after more than 2100 years.

    A pozzolan is a siliceous or siliceous / aluminous material that, when mixed with lime and water, forms a cementitious compound. Fly ash is the best known, and one of the most commonly used, pozzolans in the world. Some industrial sources of materials with pozzolanic properties are: Class F (silicious) fly ash from coal-fired power plants, silica fume from silicon production, rice husk ash from rice paddy-fields, and metakaolin from oil sand operations. Metakaolin, a powerful pozzolan, can also be manufactured, and is valued for making white concrete.
    Other industrial waste products used in Portland composite cements include Class C (calcareous) fly ash and ground granulated blast furnace slag.

    Similar to flouride, flyash would need to be treated as a hazardous waste if it wasn't used in cement.

    The reason for the uptake of cement over lime, is the speed with which cement-based concrete sets. In the reconstruction phase after WW2, speed was of the essence, thus lime gradually fell out of use in the heavy construction industries. All around the world, most reasonably sized population centres either have (in the third world), or have evidence of, lime works that provided the slaked lime for local construction. Many towns still have streets named "Lime St" or "Kiln St" or variations of those.

    Building maintenance is an ongoing thing no matter what material you make the building from. All those beautiful white homes in the Mediterranean - they get a limewash regularly applied. Same with the 9 story earth building in Yemen that has been continuously occupied for at least 2000 years.

    I'll do up some info for you on why I prefer lime to cement (maybe start a "building materials" thread) :)
     
  10. gardenlen

    gardenlen Group for banned users

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    provocative is your judgement sunburn,

    i said it along the lines i wouldn't be using it when there is better product available.

    here is an extract:

    What is fly ash?
    Coal combustion waste is also known as coal ash or fly ash. It can contain concentrated amounts of heavy metals such as arsenic, lead and selenium, which can cause cancer and other health problems.

    Read more from this Tulsa World article at https://www.tulsaworld.com/news/article.aspx?subjectid=11&articleid=20100909_12_A1_CUTLIN316180

    https://www.scientificamerican.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste

    the rest is up to you.

    len
     
  11. sun burn

    sun burn Junior Member

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    Len, How could i know on what basis you said it. Your post gave no indication. You just said you wouldn't use it.

    Its like saying, I wouldn't put milk in my tea if you paid me to. Its obvious that anyone who knows nothing about the dangers of milk would want to know what is wrong with milk after heraing you say that. That's what i mean by provocative. It provokes a question because readers are not mind readers.

    If you think there is a better product than flyash or do you mean cement, why not say what it is?

    Just because something contains heavy metals does not mean it is going to cause cancer. YOu have to consume it or ingest it. Are you planning on eating cement? Or do you think anyone else is? How else are you going to ingest this stuff? Certainly if it can be breathed in, it would be handy to know in advance so that one can take appropriate precautions. After reading that aritcle, i can see that there needs to be safe ways of transporting it about but once it is concrete it seems as though it would be inert.

    Don, i will have to read that again. Its quite technical but a quick read suggests that not all fly ashes are the same. Is that correct.

    And regarding cement versus lime. Is the speed of curing the only thing. If that's all there is to it, then i might as well use lime unless the speed of curing is really slow. I suspect there must be other disadvantages. I love lime wash.

    Yes of course all building require maintenance. I was just challenging the idea that these buildings survived as they are today in one piece from when they were built which was really how your comment sounded. Sometimes maintenance is quite major and amounts to pretty much a rebuild, although i know that often these days on historic buildings they try to rebuild using materials and methods used in the original building. Take for example the 500 year old pub. Its a certainty that the lime plaster would have been redone and is therefore not 500 years old. Likewise the thatch roof cause even i know that thatch rooves don't last that long. Maybe its only the stone that has lasted 500 years.
     
  12. DonHansford

    DonHansford Junior Member

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    Not all fly ashes are the same. Some are lower or higher in either silica or aluminium, which reflects what percentage can be mixed with PC to reach certain strength characteristics for certain jobs.

    Another downside to cement-based concrete for house construction is that it doesn't "breathe" - a wall of earth, strawbales, mudbrick, etc with a lime plaster "overcoat" will absorb and release humidity, maintaining a much healthier environment for people and animals. The lime plaster, or wash, also has the added advantage of repelling pests. Plus, when lime sets, it reabsorbs all of the C02 it released during firing and slaking.

    Just thinking on the run, if your walls don't need to support your roof, and are more for privacy than tensile strength, why not a wattle & daub style (using bamboo in place of the wattle) with a lime wash finish?

    In modern building construction, labour is one of the most significant costs. Hence the emphasis on building products that are quick to install, rather than the best for the job. Architects design houses, not to be efficient for the end user, but to be efficient for the building contractor. Hence, asking for a house design that uses such things as wide eaves, high ceilings, convection to maintain airflow through the house in summer, etc will add such an enormous amount to the building cost (because it is "outside the norm" in terms of the material sizes and "standard industry practice") that most people simply cannot justify the extra expense.

    The worst possible house to build in a flood area is a) on a slab on the ground, b) uses plaster-based wall and ceiling sheeting, c) has cavity type interior doors, and d) has little or no flow-through ventilation to help promote rapid drying following inundation. Most of the older hardwood and vj highset queenslander style homes that have been through the floods will (except for those structurally damaged by fast water/objects) will be ready for re-habitation within a few days of the water receding. Most of the "modern" McMansions will be weeks (for the lucky ones) or possibly years - those that aren't simply written off.

    Will this come out in the Royal Commission? I very much doubt it - the building industry in Qld is as much a sacred cow as the mining and gas industry is.
     
  13. DonHansford

    DonHansford Junior Member

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    In the case of cob, you simply mix some more cob, and slap it (literally) into the hole. Provided the hat (roof) and boots (foundations) are ok, these buildings have an almost unlimited lifespan.

    External plastering is patched where and when necessary and a regular whitewash applied (frequency depends on the climate - annually for harsh climes, bi, tri, or even deca - annually for more mild areas. The outer layer of thatch needs to be replaced every few years, but if this is done properly, the inner layers can last almost indefinitely.

    Here is an excerpt from a discussion forum on deatech.com :

    On Jul 22, 2007, at 2:22 PM, Kathryn Marsh wrote:

    > I've seen five hundred year old cob dissolve in a few weeks when
    > the thatch was allowed to deteriorate but my grandparents' wattle
    > and daub house was built in the 13th century and survived the 1947
    > flooding of the English fenlands when they escaped by boat through
    > a hole in the thatch. Although the cob was damaged in places it
    > dried out and was easily repaired. Same thing in the great flood of
    > 1953 - tho' that time grandad got out before the water arrived but
    > again it was flooded almost to the eaves. I think both times the
    > secret to its survival was that it was whitewashed every year and
    > that the water didn't actually get into the top of the walls. Alas,
    > it didn't survive greedy developers who demolished it to make room
    > for modern expensive executive homes in the days before the
    > protection of ancient buildings. Could have been older - the road
    > by the front gate was on roman foundations but it was only recorded
    > back to 1280 or thereabouts
    >
    > kathryn

    I'll have a go at attaching a couple of pictures - one of a 400 year old farmhouse, and one of a stone and cob wall that has been in the weather for the best part of 100 years. Both from Devon in the UK.
    [​IMG]

    [​IMG]
     
  14. sun burn

    sun burn Junior Member

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    Nice pictures. I read of cob all the time but I still don't know what it is. I haven't had the time/interest to chase it up. I suppose its just a type of earth brick or rammed earth.
     
  15. sun burn

    sun burn Junior Member

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    Are you thinking of me here. Wattle daub comes from europe doesn't it. I don't think this type of construction is suitable for a tropical climate.

    I have seen mud houses in west bengal. They have to replace the mud render every day on the front floors and i expect they have to do it every year. So itis too high maintenance for here where monsoon rains are heavy.

    I believe in trying to build for the climate just as I believe in growing plants to suit the climate. Bamboo itself would be ideal but i don't have access to enough good bamboo to do the job and it would be years before i could do it.

    If you think i should be using lime then i will use lime with a ferrocement construction. Why not if lime is so good?

    Ordinarily i do not think cement is good for this climate if its in the sun where it can heat up. But for the bathroom, i can protect the walls and roof from the sun by plants and in my actual house, the shade from the forest trees will protect it from heating up.

    One thing about ferrocement, it's low maintenance.
     
  16. sun burn

    sun burn Junior Member

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    Don! Don! I am so excited. Thanks for putting me on to the idea of lime. I am going to go exploring it and testing it and so on. I have just ordered a book from Amazon about building wiht Lime. And then i cancelled it but that's another story. I will buy it.

    I also spoke to the guys from Mirriwinni Lime. Its the local lime miners. Although a bag of lime and a bag of cement seem to cost about the same price, i have been assured that for a truckload there will be a price difference. But if lime is so good and it possible to work with it here and build a house using it, I will do it. Cause it sounds like its a lot better for the planet as well as for my pocket.

    I also ordered my tree house book. I do hope you can build a house out of lime that is not just using lime for mortar because that will be a big disappointment if htat is the only way it can be used. See my members thread latitude 14 blog for more details on progress.
     
  17. FintanK

    FintanK Junior Member

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    I have been using MinPlus Rock Dust for number of years and I have noticed a big difference in my garden soil and the worms love it.

    I had recently read about the beneficial effect of rock dust on forests affected by acid rain in Germany.

    Last week I was visiting a building site where a bag of cement had burst open and been left on the ground a few months ago. I noticed that the weeds in the immediate vicinity of the bag of concrete were considerably bigger than other weeds which were uphill of the burst bag. This made me wonder were the weeds potentially accessing nutrients from the now solid concrete. I suppose the weeds may have been getting additional moisture from under the bag. This may seem to be a strange thing to be interested in,
    but these sort of thing intrigue me.
    Thanks
     
  18. sun burn

    sun burn Junior Member

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    Then they must be benefiting from the lime in the cement. It must have neutralised an acid soil or something like that perhaps. If not the lime then something else in the cement is doing something to the soil.

    Are there any minerals in portland cement?
     
  19. gardenlen

    gardenlen Group for banned users

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    in use in the garden, lime just can't be used willy nilly 1st the soil needs to be acid and then the gardener wants if changed to alkaline, then there is application rate, so in the garden when we need lime we use dolomite. where lime isn't needed we sue gypsum always and heaps of it.

    also can't see any financila benefit in buying and using cement when rock dust is probably cheaper.

    also check the road sides especially in rural when they use crusher/cracker dust (blue stone) the growth in the immidiate vicinity is always greener. and cracker dust is not expensive at all.

    len
     
  20. sun burn

    sun burn Junior Member

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    Len, i doubt that the OP intended going out to buy cement to apply to the garden. I suspect if were to use it it, would be from found stuff and as a way of recycling it.

    Back to the topic of lime V cement, i put the discussion to the ferrocment forum i am using and this is their discussion. It seems it may not be suitable for me after all. The main point being that lime as a building material always seem to be used in mortar to fix stone to each other. However, the discussion isn't complete and i need more info and shall have to do further research but for now it looks as that idea has been scotched. But still i will try to do some tests with it to see for myself what its like to use.

    https://ferrocement.net/flist/index.php?topic=245.0
     

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