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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorNedington
    • CommentTimeMay 25th 2019
    As part of our plans for a cement free straw house project we need to build a large workshop.
    What materials would people suggest for the floor?
    It needs to be waterproof, load bearing and non-flammable due to things like welding, metal and timber fabrication and all sorts of other things going on. Need to be able to bolt down machinery too.
    It'll have to be limecrete then, unless you have anyone locally scrapping any huge flat chunks of steel!
    • CommentTimeMay 25th 2019
    I agree with Nick. You could also consider something like paving slabs or quarry tiles over , although one difficulty would be in ensuring a flat enough surface that stays flat over the years.

    It was Bill Steen that persuaded me that cement and concrete was not the root of all evil (in a bar in a YHA in the Lake District of all places). Yes, OPC is not good and is used in vast quantities around the world, which gives it a bad rep, but it's usually used in a lower percentage in concrete than lime is in limecrete so it kind of balances out. And it's a lot easier to use and to obtain with recycled additives these days. That persuaded me to accept it in the floor of our SB house.
    • CommentAuthorjfb
    • CommentTimeMay 26th 2019
    I'm not convinced how waterproof a limecrete floor would be. Not sure what sealing options there would be.
    How strong is limecrete with regard to bolts pulling out with (vibrating?) machines fixed down?

    Can limecrete have rebar built in the same as concrete?
    • CommentTimeMay 26th 2019
    I'm not sure Kathryn meant waterproof as in 'keeps water out'. Concrete doesn't do that either. But both are stable in water; they are not destroyed by it.

    Non-flammable would be an issue if it needed to be sealed. Something like a traditional oil or wax seal would be flammable, and I suspect a lot of resins might be too, although I don't know.
    • CommentAuthorCWatters
    • CommentTimeMay 29th 2019 edited
    Presumably you are avoiding concrete because it's perceived to need a lot of energy to make it? I think concrete uses less than bricks or blocks on a per kg basis.


    If other solutions need rebar that might mess up the figures as steel needs quite a lot as well.

    Perhaps use concrete and mitigate the C02 another way?
    Posted By: CWattersPerhaps use concrete and mitigate the C02 another way?

    Doesn't work in my book - If you are going to be able to mitigate the CO2 in another way why not do that anyway irrespective of using the concrete.

    IMO there are times when the use of concrete is justified, e.g. if the alternatives do not provide an as good alternative. The embodied energy of lime I understand is not a lot different to that of cement and a higher %age of lime is needed in limecrete than cement in concrete. The locally availability of the materials is also a factor.
    I found an interesting chart at
    which showed that the embodied energy of concrete was 1.9 whereas clay bricks were 2.5 and kiln dried softwood was 3.4

    Any saving made today may be outweighed by any repairs needed in the future due to the chosen floor not being up to the long term use of a workshop
    The embodied energy is only part of the story though, much/most of the co2 emissions from cement production comes from the calcination reaction of the lime component of the cement production process.

    CaCO3 > CaO + CO2

    The various stats that are thrown around (often by interested parties) may ignore this, or may ignore that it takes many more tonnes of concrete to produce a floor than it would take tonnes of softwood. The aggregate for the concrete has to be trucked longer or shorter distances depending on where your site is, but timber usually has to come a long way. Also the concrete might last longer than the timber and be crushed and maybe recycled, whereas the timber at end of life will eventually end up biodegraded or burned. Pure Lime emits lots of CO2 in manufacturing, but will reabsorb much of it over a life time, unlike the lime in cement. Overall it seems difficult to come up with any simple conclusions about one material being 'bad' or 'good'.
    Re the OP, my grandad tells me that workshop floors were traditionally a dry mix of gravel sand lime and soot, compacted down hard, with benches and machines bolted down to railway sleepers set in the floor. He also worked places with brick floors.
    • CommentAuthorgyrogear
    • CommentTimeMay 31st 2019
    Posted By: WillInAberdeenRe the OP, my grandad tells me that workshop floors were traditionally a dry mix of gravel sand lime and soot, compacted down hard, with benches and machines bolted down to railway sleepers set in the floor. He also worked places with brick floors.

    I love it !

    • CommentAuthorCWatters
    • CommentTimeJun 2nd 2019 edited

    " Surprisingly, concrete is very low, especially when compared to hydrated lime, which I am still trying to make sense of. Jacob Deva Racusin and Ace McArleton have this to say about lime in particular:

    As we see from the chart, lime has a comparable embodied energy to cement — by some calculations, even greater — despite lower kiln temperatures in its firing (potential causes include longer firing times, fuel sources, and production efficiency.) However, its embodied carbon cradle-to-grate is lower, and these metrics do not factor in carbon sequestration during the curing process, which is greater for lime than cement."
    • CommentTimeJun 2nd 2019
    Yes. The source data, which was Hammond & Jones 2011 Inventory of Carbon & Energy said:

    "Data on cement has been brought in line with British Cement Association data.

    "We have worked with the concrete centre to revise the ICE cement, mortar and concrete model, underlying data and materials profiles. Consequently the data is much improved."

    They also say:

    "Lime is often chosen as an environmentally friendly material. It was therefore surprising to learn that the embodied energy of lime was slightly higher than for cement. This was observed from the respectable sample size of 39 data records. Lime is fired in the kiln to a lower temperature than cement, which is often misconceived as proof for a lower embodied energy. The present authors suggest that yield, density, and time in the kiln are all vital parameters to total energy consumption and that firing temperature may not be used as a proxy for embodied energy. This is presented as a possibility for its higher embodied energy. It should be noted that embodied energy is, in itself, not evidence to discredit limes environmental credentials. Due to a more favourable fuel mix and slightly lower process related carbon dioxide emissions lime has a lower embodied carbon than cement. An additional benefit of using lime based mortar includes the increased ability for deconstruction, rather than demolition. The re-carbonation that occurs over the lifetimes of both cement and lime based mortars (when exposed to air) will reduce the embodied carbon impact of the materials. Its understood that this process is not undesirable for lime (unlike cement). Examination of lime's full carbon cycle, cradle-to-grave, is therefore necessary."

    To me, both imply that the data may not be terribly reliable.

    The fuel mix is also important and has probably changed significantly over the past eight years. I expect that coal has been a major source for OPC ever since it was invented. Traditionally, lime-burning was fueled with timber, although no longer except in unusual sites.
    >> "concrete is very low, especially when compared to hydrated lime"

    But concrete is surely not comparable with hydrated lime? Concrete is mostly inert sand and aggregate. A fairer comparison would be UNhydrated lime vs dry cement? Cement would look more favourable than lime on that basis.

    The article is well intentioned but it does flip between embodied energy and embodied carbon. These are dramatically not the same thing for lime, which is just what's left once you cook the CO2 out of limestone (where it had been sequestered for millions of years).

    It doesn't address that you need fewer kgs of timber than lime to build a house, and the data sourcing is not transparent (djh has traced some back to the cement industry). As I said,

    >> it seems difficult to come up with any simple conclusions about one material being 'bad' or 'good'.

    Lime is traditional, like with steam locomotives, traditions are worth preserving but are not always great for the environment!
    • CommentTimeJun 2nd 2019
    Posted By: WillInAberdeen>> "concrete is very low, especially when compared to hydrated lime"

    But concrete is surely not comparable with hydrated lime? Concrete is mostly inert sand and aggregate. A fairer comparison would be UNhydrated lime vs dry cement?

    I absolutely agree that it's entirely wrong to compare concrete with lime. Concrete should be compared against limecrete or else cement (OPC) should be compared against lime. I do think that hydrated lime is the correct type of lime to compare against OPC though, since that's what you mix with water and aggregates to make limecrete.

    Unhydrated lime is quicklime, which is a different and dangerous beast. Hydrated lime is a powder sold in bags, just like OPC.

    As to tracing references, I believe it's possible to trace back most if not all of the data use in constructing ICE. Just go back to the original documents and trace back from there. I for one have simply never bothered doing it.
    Hydrated (slaked) lime Ca(OH)2 weighs 30% more than the unhydrated (quick) lime CaO from which it is made.

    As the embodied carbon numbers are presented on a kgCO2/kg basis, the greater weight of hydrated lime gives a flatteringly lower figure for its embodied CO2 than for unhydrated quick lime or OPC.

    Dry cement is comparable with unhydrated lime, as it is mostly unslaked calcium oxide, chemically bound with oxides of silicon aluminium magnesium iron and sulphur . This is what makes it get warm and caustic when mixed with water, similar to slaking quick lime, though the heat is tempered by the other metals and by the sand/aggregate.

    Cement cannot set without water to slake these oxides, which converts them to hydroxides and hydrates, similar to slaked lime. The additional metals and silicates makes it capable of setting hard quickly (mineralisation) in the hydroxide form, without requiring slow air carbonation to set, which pure slaked lime does.

    Quick lime is equivalent to dry cement (unslaked oxides)
    Slaked lime is equivalent to set cement (slaked hydroxides and hydrates)
    Set lime has no direct cement equivalent (carbonate)

    Edit: not to be confused with 'hydraulic' lime NHL which is chemically similar to cement, made from limestone containing natural clay impurities that supply the silicates etc
    • CommentTimeJun 3rd 2019
    It's moot arguing about comparing cement and lime. What's important are the figures for the substance as used, i.e either concrete versus limecrete or cement mortar vs lime mortar depending on the use case.
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