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slaking quicklime

I have been slaked my own lime several times, usually slaking 1/4-1t quicklime at a time. I've always used calbux 90, a 90micron fine powder also from Buxton. The result is very good putty and the process is.... hot and dusty. I cover up completely, then crawl out of sweaty dusty mask and overalls at the end. I think the pebble would remove the dust, (which gets carried by rising steam) and much of the hazard from the process...? I imagine though a slower reaction, how long do the pebbles take to break down and react? I think most of the reaction is over in a minute with the powder. Any comparative experience? Thank you very much
Simon

8 thoughts on “slaking quicklime”

  • Adam Brown

    Hi Simon

    Apologies for the delay in response (some teething trouble with my site access).

    From our testing with hot mixed mortars we have found that the pebbled quicklime poses less risks in terms of 'pluming' of the binder. Due to its greater density and surface area the pebble is not as easily thrown into the air, compared with the powdered quicklime. The one thing to watch out for with the pebble is the isolated hot spots. During mixing the reaction temperature overall will not reach above 100C, however the actual pebbles themselves can go beyond this temperature.

    In terms of the breakdown that will partly depend on your water addition rate, so it is difficult to say. The process is slower with the pebble and you can have a delayed reaction when compared to the powder. For our lime putty production our processing procedure is quite advanced and is automated, so all of the timings are controlled.

    Reply
  • Cath Coffey

    Greetings,
    Do you think that a sturdy plastic rubbish bin can withstand the temperatures? Alternately I have a galvanised metal bin....wondering if the quicklime would react with it?
    I have 25kg of powdered quicklime to slake for lime putty. Once slaked, I'll leave it for 6 months before I use it.

    Reply
    • Adam Brown

      Good Morning

      I have seen it done in metal rubbish bins. Although it would be best left till warmer weather as colder temperatures can effect the process and the final material.

      However we don't generally recommend people to mix their own putty as it is quite an industrial process and at home/on site mixing processes and set up will usually result in a poor quality material. When mixing in containers or buckets water is not released at sufficient rates and is retained within the putty and this leads to a very wet and often unusable material.

      Kind Regards

      Adam

      Reply
      • Cath Coffey

        Thanks for the quick response Adam. I appreciate your advice.
        I have had some experience with mixing NHL3.5 for putty for mortar and lime wash. It worked quite well...made a low stone wall and pathway which is still going strong a year later. Fingers crossed! The lime wash was for an earthbag roundhouse...5 layers inside and out!

        I want to move on to quicklime putty because I understand it is stronger. I need to mix it myself, because I have a large job to complete in an eco build, and can't afford to buy all the lime putty I need.
        I'll be making a stone foundation for a wood cabin, and a couple of stone retaining walls.

        I have a heavy duty paddle mixer, a large plasterers mixing bath, metal bins and a host of airtight plastic buckets to store the completed putty in.
        .....and time to try and do things properly.

        Can you give me any pointers on the best way to do the mix to ensure good results?
        Any advice most welcome.

        Kind regards,
        Cath

        Reply
        • Adam Brown

          When using NHL to create a putty was this mixed up, left overnight and used the following day?

          Slaking a quicklime to create a lime putty is a different process and using a quicklime to create a putty would make a much weaker material.

          The only real tip i can give you is trying to release water so its not retained within the putty. Unfortunately as we have an industrial set up here our mixing process is very different and I can't really comment on site mixing.

          Kind Regards

          Adam

          Reply
  • Cath Coffey

    Hi Adam,
    No...I left the NHL putty to slake for 3 months, always with a water cap, by which time it had doubled in size. It did harden but was easily loosened with the paddle mixer. At first I mixed it every 2 days for about 2 weeks, then once a week. The texture was like a very smooth thick cream cheese...it held shape when i drew a knife through it, and was easy to mix for the mortar and casein lime paint I eventually used it for.

    I'm not sure what you mean by" trying to release water"? How do I do that? By thorough mixing?

    My research so far has told me that slaked lime putty would be stronger than that made with NHL. Am I wrong?
    There is so much misinformation out there, which is why I'm approaching your company...people with actual experience in slaking quicklime for putty.

    Re the slaking process....I'm aware of the exothermic reaction when adding it to water, and the importance of safety protection for lungs, eyes and skin.

    I guess my questions are as follows:
    1) What ratio of water to CaO powder do you advise?
    2) Once mixed, should I continue to stir it daily, then weekly as I did with the NHL, or just leave it to do it's own thing?
    I intend to leave it to mature for at least 5 months.

    Once again- really appreciate you taking the time to reply.

    Kind regards,
    Cath

    Reply
    • Adam Brown

      Hi Cath

      NHL isn't usually slaked, it is pre-slaked and then bagged before it is sold. Putty can be made from NHL, but it needs to be used within 1 or 2 days, otherwise the hydraulic set is broken and a large part of the binding capacity of the lime is lost. From what you have described it sounds like the free lime contained within the NHL, which would have been left over, has held together the mortar and limewash and this would likely produce a weak mortar. We would strongly advise against using the material this way, but as you say it looks to have worked to some degree in your application.

      As a binder, NHL is stronger than quicklime, so I am not sure where that information has come from.

      As I mentioned previously we don't ever recommend slaking quicklime to create a putty, this isn't a commercial decision, but because it can be a difficult and an extremely dangerous process. I don't want to sound condescending in any was here but it can start fires if in contact with paper/wood & water, it’s dangerous to store, it’s very difficult to dispose of, it can near instantaneously blind you in powder form and can cause severe chemical burns to skin if inappropriately handled. That said you already have the quicklime and there are limitations to purchasing putty. Sufficient and suitable PPE should be the main priority, we would suggest a full face mask/respirator, eyewash always being available and suitable clothing, chemical resistant gloves etc.

      With non-hydraulic quicklime the less water the better during the first mixing phase, it wants to run to a thick cream consistency and then not be remixed after it has been laid to settle.
      Figures for water addition will depend on the source/manufacturer and granulometry of the quicklime, so unfortunately I am unable to help here. By not remixing you will allow the reacted lime to release some of the excess mixing water and get to an appropriate solids content for use as a building mortar. Normally you don’t need to add water to the top of the material after as it will naturally settle some water out anyway.

      Mixing buckets, tools and working surfaces need to be metal or a type of stone which can deal with rapid temperature changes

      Kind Regards

      Adam

      Reply
      • Cath Coffey

        Thank you so much for this very useful information Adam.
        I truly appreciate you taking the time to answer all my queries in depth.

        I'll leave you alone now.

        Reply

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