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    • CommentAuthorSimonD
    • CommentTimeFeb 2nd 2021
     
    I thought I'd just put this out here to find out if anyone has any experience with this.

    I've got a whole load of woodfibre EWI that's been sitting in my house waiting to be installed and rendered. Unfortunately I ran out of time last year before autumn and winter and I'm now planning the installation for spring.

    Normally this stuff is rendered using a proprietary hydraulic lime system. However, I've been considering using non-hydraulic lime instead. In discussions elsewhere with the lime community, I've received some different opinions. Some say no way jose, and some say absolutely fine and would be great.

    I don't want to discuss why I'm considering the non-hydaulic lime as I don't have any major compelling reasons other than that I would prefer the finish on my project. I'm doing it myself and although harder physical work, the non-hydraulic lime can be more forgiving of mistakes allowing time for re-work too. I also don't mind experimenting with things that are a bit different.

    I'm leaning towards the fine side and at pains to think of reasons non-hydraulic lime couldn't be used on woodfibre.Those who've said not haven't been able to give me a well articulated reason why not. I'm aware that Pavatex supply/supplied a woodfibre IWI board that is fine with non-hydraulic lime plaster.

    Do you have experience using non-hydraulic lime with woodfibre insulation? Any thoughts?
    •  
      CommentAuthordjh
    • CommentTimeFeb 2nd 2021
     
    I don't think there'd be any problems, though you might want to think about keying the wood fibre a bit to be sure of initial adhesion. We have woodfibre batts around our windows, oversailing the frames, but we chose to cover those with woodwool boards to get a good adhesion key. We haven't had any cracks or anything in those areas. I can't think of any reason why you couldn't do it direct; it might be a better surface than many.
    • CommentAuthorSimonD
    • CommentTimeFeb 3rd 2021
     
    Thanks, that's reassuring. The stuff I have is surprisingly textured and fluffy on the outside which makes me suspect using a good amount of pressure on the base coat may be okay.
    •  
      CommentAuthordjh
    • CommentTimeFeb 3rd 2021
     
    Ah OK, our wood fibre batts were fairly hard and smooth all over as I remember.
    • CommentAuthorjfb
    • CommentTimeFeb 3rd 2021
     
    i'm a bit confused - if by non-hydraulic lime you mean hydrated lime isn't that just used as a plasticizer in conjunction with cement. On its own hydrated lime and sand won't go off properly as it needs the cement.

    Maybe I have misunderstood what you mean by non hydraulic lime.

    Also - what do you mean by 'leaning towards the fine side'? Do you mean fine sand?
    Be aware that using an overly fine sand will lead to a weaker finish which wouldn't be something I would be happy with.

    How much rendering experience do you have? A lot of the finish you get isn't so much to do with the grading of the sand but with how it is applied and when you rub it up to a finish. Why are you so against the proprietary hydraulic render? Cost I could understand. I made my own sand/hydraulic lime render for woodfibre IWI and that has worked well.

    Which woodfibre board do you have?
    Are you planning on a mesh as part of the rendering?
    • CommentAuthorSimonD
    • CommentTimeFeb 3rd 2021
     
    Posted By: jfbi'm a bit confused - if by non-hydraulic lime you mean hydrated lime isn't that just used as a plasticizer in conjunction with cement. On its own hydrated lime and sand won't go off properly as it needs the cement.

    Maybe I have misunderstood what you mean by non hydraulic lime.

    Also - what do you mean by 'leaning towards the fine side'? Do you mean fine sand?
    Be aware that using an overly fine sand will lead to a weaker finish which wouldn't be something I would be happy with.

    How much rendering experience do you have? A lot of the finish you get isn't so much to do with the grading of the sand but with how it is applied and when you rub it up to a finish. Why are you so against the proprietary hydraulic render? Cost I could understand. I made my own sand/hydraulic lime render for woodfibre IWI and that has worked well.

    Which woodfibre board do you have?
    Are you planning on a mesh as part of the rendering?


    By non-hydraulic, I'm referring to traditional lime putty not the dry hydrated lime used as plasticizer (although I've been told this can be used and made into a putty by soaking it for a few days - but quite inferior to proper lime putty mind you).

    By leaning to the fine side I meant that I'm taking the optimistic view that it should be fine.

    I'm not particularly experienced in render and I do have a large area of hidden wall which will be the first pass :bigsmile:

    I have the woodfibre boards from Scheider-Holtz and yes, will be using a mesh.
    •  
      CommentAuthordjh
    • CommentTimeFeb 3rd 2021
     
    Posted By: SimonDBy non-hydraulic, I'm referring to traditional lime putty not the dry hydrated lime used as plasticizer (although I've been told this can be used and made into a putty by soaking it for a few days - but quite inferior to proper lime putty mind you).

    Good, that's what I'd assumed. I believe you're right about hydrated time too and I would expect it to set in a similar time to lime putty - days or weeks, rather than hours.
  1.  
    >>>>"i'm a bit confused - if by non-hydraulic lime you mean hydrated lime "

    Hydraulic, hydrated, non-hydrated and naturally-hydraulic - why did they choose such similar words to mean different things?

    Hydraulic Lime contains calcium silicate, chemically the same as cement. This takes up water, to make a complex mineral structure of calcium and silicon oxides and water. This happens rapidly and can set underwater.

    Hydraulic Lime can be NHL, where N stands for Naturally. There are grades NHL2, NHL3.5 and NHL5 depending on how Naturally Hydraulic it is. It is made from certain limestone quarries which naturally contain the right amount of silica (clay).

    Non Hydraulic Lime (careful with the abbreviation, this isn't NHL) sets when carbon dioxide from the air dissolves in and reacts with calcium hydroxide, the main component of hydrated lime. The dissolving takes days/weeks/more and must be in contact with air. Some people think that non-hydraulic lime is a 'green' building material, in comparison to NHL or cement, because it reabsorbs more of the CO2 emitted during manufacture.

    Hydrated lime is any lime after the hydrating (slaking) step of its manufacturing when the calcium oxide is converted to calcium hydroxide. Could be hydraulic, NHL or non hydraulic depending if it also contains some calcium silicate.

    If lime has not yet been hydrated then it is Quicklime or Hot Lime, which is a bit hazardous.

    Lime putty is hydrated lime that has been left standing in water for several months so it is really well hydrated and protected from CO2.
    •  
      CommentAuthordjh
    • CommentTimeFeb 3rd 2021
     
    Posted By: WillInAberdeenHydrated lime is any lime after the hydrating

    Technically correct, but is more often used to mean the bagged stuff.

    Lime putty is hydrated lime that has been left standing in water for several months so it is really well hydrated and protected from CO2

    It shouldn't be. Lime putty is normally made by slaking lumps of quicklime (which have come from the kiln) with excess water. The lime breaks down into smaller and smaller pieces during the process and is left for at least three months to mature as you say.

    Hydrated lime is made by slaking with exactly the right amount of water, after which it is bagged and sold.

    Non-hydraulic lime is traditionally called 'air lime' or 'fat lime', especially when putty, which are less easily confused with hydraulic lime.

    See https://www.buildingconservation.com/articles/limebasic/limebasic.htm
  2.  
    >>> "Hydrated lime"..." used to mean the bagged stuff"

    Hydraulic and non-hydraulic and partially-hydraulic lime are all sold in bags and they will (nearly) all be hydrated. If they are hydraulic then they will be marked and sold as such. If you ask for 'bagged lime' you will probably get something hydrated but not very hydraulic.


    >>> "Lime putty is hydrated lime"..."It shouldn't be"

    Yes it should. Lime putty is quicklime that has been hydrated with excess water. The resulting hydrated lime is left standing in the excess water for months to fully complete the hydration reactions. The lumpier the quicklime, the longer it takes. These reactions include hydration of whatever silicates, aluminas, iron, magnesium, etc, that were present in the limestone, which otherwise would make it a little bit hydraulic.
    •  
      CommentAuthordjh
    • CommentTimeFeb 4th 2021 edited
     
    Posted By: WillInAberdeen >>> "Hydrated lime"..." used to mean the bagged stuff"

    Hydraulic and non-hydraulic and partially-hydraulic lime are all sold in bags and they will (nearly) all be hydrated. If they are hydraulic then they will be marked and sold as such. If you ask for 'bagged lime' you will probably get something hydrated but not very hydraulic.

    Now you're getting desperate. Of course hydraulic limes are sold in bags. Otherwise they would rapidly set. When I said bagged stuff in the context of hydrated lime, I was of course referring to bags of hydrated lime and if you try to buy that you will get exactly that. Anybody asking for 'bagged lime' deserves what they get - confusion on the part of the shopkeeper, I expect.

    >>> "Lime putty is hydrated lime"..."It shouldn't be"

    Yes it should. Lime putty is quicklime that has been hydrated with excess water. The resulting hydrated lime is left standing in the excess water for months to fully complete the hydration reactions.

    And now eliding the context to make it look like you said something you didn't and I said something I didn't. I recommend people to read what you originally wrote and what I originally wrote in context to decide who was right.

    I'm disappointed, Will. You normally talk enough sense to earn my respect.
  3.  
    Good grief.

    >>>"I recommend people to read what you originally wrote and what I originally wrote in context to decide who was right."

    Good recommendation.
    • CommentAuthorSimonD
    • CommentTimeFeb 5th 2021
     
    I don't have enough experience working with lime to provide my personal input on this, but for the sake of future visitors, perhaps I can quote from the best book I've so far used to learn about this fascinating topic. It's only about 30 pages long. It's called "Lime in Building: A Practical Guide" by Jane Schofield (Revised 3rd Edition). I bought my copy from The Society for the Protection of Ancient Buildings https://www.spab.org.uk/. I highly recommend it and worth every penny of the £8 or so it cost me.

    (pages 3-5)

    "Non-hydraulic lime is produced by burning limestone (Calcium Carbonate CaCO3) during which process Carbon Dioxide (CO2) is driven off. The resulting 'super-dry' material is quicklime (Calcium Oxide (CaO). When mixed with water (H2O), this reacts violently and boils. This is called slaking. The resulting slurry is lime putty (Calcium Hydroxide (Ca(OH)2) which is stored in amoist state until used..

    This non-hydraulic lime is so called because it requires exposure to air to carbonate, and will not set under water. This is the most permeable of all building limes, andthe most appropriate lime to use in the conservation of old buildings where maximum permeability is required.

    Hydrated lime or 'bag lime', a non-hydraulic lime available from most builders merchants, is produced by slaking with a precise amount of water which is driven off during the reaction, resulting in a dry powder..

    Hydrated lime has regularly been used as an extender or filler in cement mixes, but its uses as the principal binder is limited..

    Hydraulic lime is produced from limestone containing clay and makes its set partly by achemical reaction with water, without exposure to air, but also by carbonisation. It can set under water,hence its name. In the ten years since this guide was first published,the availability of, and interest in, hydraulic lime hasincreased enormously in the UK. There is also a great diverity of opinion on the benefits (or otherwise) of using hydraulic lime and urgently-needed research is only now being undertaken.

    Hydraulic lime is a blanket term fora range of materials with widely ranging properties which are usually referred to as follows:

    Feebly hydraulic lime is defined by having less than 12% clay, which will mkae a set under water after about 20 days. It is usuallyand off-white colour,and makes a fatty (fairly sticky) mix which is easy to use. Feebly hydraulic lime is produced in the UK, frequently from blue lias or some chalks.

    Moderately hydraulic limes contain 12% to 18% of active clay and sets under water in about 15-20 days. Some UK produced limes fall into this category; they are generally pale grey of (stet) buff-coloured. The mortar is less easy to use as it is not so sticky.

    Eminently hydraulic limes have up to 25% active clay, make an initial set in a matter of hours, and is hard in a couple of days. It is a darker colour than other limes, and makes a mortar which is rather crumbly and difficult to handle when wet. All eminently hydraulic limes presently for sale in the UK have been imported, usually from France or Italy. Some contain cement (see page 5) or pozzolanic additives (see page 10) to keep their performance consistent.

    French hydraulic limes are classified with a NHL number (HNL stands for natural hydraulic lime). Commonly available are NHL 2 which is moderatly hydraulic,NHL 3.5 which could be described as almost eminently hydraulic and NHL 5 which is eminently hydraulic.

    Hydraulic lime is normally supplied in hydrated form (dry powder) although some feebly hydraulic lime is available as quicklime or short life putty."
    • CommentAuthorSimonD
    • CommentTimeFeb 5th 2021 edited
     
    As for my decision, after yet another long conversation about the various merits of types of lime and substrate, and untangling where I'd got caught up, unawares, in the "diversity of opinions" quoted above, I have actually changed tack to go for a hydraulic lime render on the woodfibre.

    Basically the upshot is that far more is known about the compatibility of hydraulic lime render mixes on woodfribre insulation than non-hydraulic and therefore I might be taking a rather untested and experimental route with non-hydraulic. Given how much I've spent on the woodfibre, I've decided it's sensible to take the more regular path with these materials.
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