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Lime mortar/ render/ putty - what to use, large cracks, wall render, skim coat

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  1. #1
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    Default Lime mortar/ render/ putty - what to use, large cracks, wall render, skim coat

    Hi there
    Despite there being some discussion on this forum already about lime/mortar/putty, we are not allowed to bump threads more than 365 days old..... So....

    Renovating my 1927 double-brick Cal Bungalow. Handmade clay brick walls, lime mortar, lime plaster. I'm lucky it's in mostly original condition, because it hasn't been stuffed up too much with gypsum and concrete.

    Original lime/sand render over the bricks is around 10-12mm consistently, then with a skim coat of lime plaster, <1mm. Around the cracks there are larger voids up to 40mm, which I've filled with a filler rod and cleaned from dust and debris. I need the following:
    • - mortar mix for large repairs up to 40mm
    • - mix for 2-3 coats of render each around 5mm thick
    • - skim coat before painting with breathable paint


    I've already done a small repair using dry hydrated lime and sand mixed 1:3. But before I take this further, I need to confirm the render mix.

    Should I make a lime putty? Sounds easy enough using hydrated lime and water, letting it sit for a week under a layer of water. Is standard brickies hydrated lime ok for this (ie 20kg hydrated lime $20 bunnings)
    Will there be a difference in:
    • - the lime mortar made from dry hydrated lime/ sand vs
    • - lime mortar made from lime putty (hydrated lime mixed to a paste and rested for a week) and sand?

    Can I use the exact same mix for the three layers of render, perhaps making the top coat more limey than the one below (eg 1:2 mix)?
    Can I use a watered version of lime putty for the final skim coat?

    Some people have recommended cornice cement as the final skim coat, but I can't see how this is any different from using gypsum. Bearing in mind I need the whole system to be breathable

    Getting correct information on hydrated lime/ hydraulic lime/ non-hydraulic lime and lime putty is proving hard!!!.....thanks for any clarifications

  2. #2
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    just got a couple of photos - the large cracks aren't that bad

    Will lime mortar 1:3 hydrated lime:sand be ok for these? Or maybe 1:4 lime:sand for the large filling mortar, then increase the lime content in the progressive layers up to 1:2 lime to very fine sand - or maybe even just diluted lime putty for the final skim coat?

    Lack of consistent information on the internet. Keen to hear of anyone's direct experiences here, especially using powdered hydrated lime, many thanks
    img20200101091455.jpg
    large cracks with filler rod - should I replace the filler rod with lime putty, given that lime has the self-healing properties in regards to building movement - and will powdered hydrated lime from Mitre10 be ok to make my own lime putty with? I read somewhere that dry hydrated lime will weaken over time if left to soak, in contrast to quicklime.
    img20200101091504.jpg
    angle shot showing depth of the original lime render, and the final lime skim coat under the paint layer. Can I use 1:3 lime:sand mortar mix for this render?

  3. #3
    Community Moderator phild01's Avatar
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    Quote Originally Posted by debunk View Post
    Hi there
    Despite there being some discussion on this forum already about lime/mortar/putty, we are not allowed to bump threads more than 365 days old.....
    You can have it bumped if you pm a mod with the url.

  4. #4
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    HI everyone, I'm updating this thread. I've now made a bucket of "Lime Putty" using standard brickies hydrated lime (from hardware store)

    Before I spend hours mixing it into a mortar and rendering it all over my walls, can anyone tell me whether they have had any success with the standard hydrated lime, or do I really have to shell out for ready-mixed lime putty from WA? Apparently, other states in Australia have banned the use of the lime to make the putty, and it's only available in WA ATM - there are distributors in NSW and Vic, but the cost is around $35 for 20kg.

    PS photo for your curiosity, see photo - the lime putty I made was simple to do and became a nice creamy consistency quite easily (with apologies to my hard-working drill)
    img20200103122218.jpg

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