This is a short post showing videos and photos of the Diathonite being applied. It was a busy three days. BorderLime worked really hard and did a superb job. We worked alongside them, with Tom on the mixing machine. You can see from the videos the speed at which the product goes on to the walls, and the mess it creates. It really was worth masking stuff up thoroughly, although we still spent several weeks vacuuming fragments of cork and lime dust.

The finished result was transformational. We’re yet to experience a winter with it, but I’ll post an update when we have some more feedback on its performance.

Videos of Diathonite Application

Diathonite Mixing Machine in action

This video shows the diathonite mixing machine in action. A bag of Diathonite Thermactive is placed onto the top of the hopper. The serrated edge cuts the bag open. The top and bottom of the bag are lifted up to pour the dry mixture out. It filters down through the grille into the hopper where it is dosed with the correct amount of water, and mixed up. It is then pumped into the building through the hose and sprayed onto the wall.

Spatter coat application onto smooth substrate

This video shows the first “spatter” coat of Diathonite Evolution being applied to a bare brick internal wall. The hose brings the Diathonite into the building from the machine which is mixing it up outside.
The spatter coat serves as a “key” for the proper base coat to adhere to – this is important if the substrate is not very grippy, as was the case with these smooth bricks. It was left to dry for a short while prior to the base coat being sprayed on at a thickness of up to 20mm.

Spraying the second coat onto the stone walls

These two videos show the application of the second coat of Diathonite Thermactive, the day after the base coat was applied in the same way, and roughly trowelled off. The Diathonite goes on in a continuously sprayed “worm”, which is then trowelled by hand to make a uniform finish. This coat will be left to dry for a couple of weeks prior to hand finishing with a lime plaster.

Trowelling off the second coat

This video shows the Diathonite being smoothed off after the second coat has been sprayed on. It is trowelled by hand to achieve a finish which is ready for a final coat of lime plaster.

Photos of Diathonite Application

To read about how we decided to use Diathonite and how we prepared for the installation, read the other posts.

19 comments to “Diathonite Insulating Lime Plaster – Part 3, Installation”

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  1. Karl Roscoe - 30th August, 2019 Reply

    Great stuff, thank you once again for sharing.

    In the picture ‘Finished top coat and the join into stone wall…’, regarding spray the ‘left’ wall, is the ‘left’ wall partly external or completely internal? I’ve been thinking about spray diathonite three inches into a room on the internal wall that meets an external wall? Your left wall looks like at least a couple of feet and so interested to know the reasoning there.

    Where did you apply the Deumix? In for the first foot up a wall where rising damp was an issue, then continue with Thermactive or Evolution?



  2. LoisLogsLune - 17th September, 2019 Reply

    Hi Karl,
    Thanks for your question. The wall in that picture is in fact the external gable wall. In a yet-to-be-published post, I will explain the detailing of the gable, but in summary the gable had a new stone wall built on the outside of it, and a fully filled cavity using Dritherm. So whilst this wall is now insulated, there is the thermal bridge between the “external” insulation in the gable, and the internal diathonite (see the detail in the sketch
    We returned the diathonite approximately 1m along the gable wall. I suspect that 3 inches won’t really provide much benefit, but our 1m corresponds to the purlin above, so was a natural place to take it to.

    The Deumix was applied to two areas for the first 1m height on the external back wall of the property which is actually below ground level outside (albeit with external insulation, tanking and suitable drainage). Whilst these were not specifically “problem areas”, both were in corners under the stairs, and so had limited air flow. The carpets which were there were mouldy and smelled bad, and there was a general sense of dampness. Whether this was rising damp or just stagnant air in a cold corner is difficult to say, but we took the opportunity to apply the Deumix whilst doing the rest of the work.

    When we returned from a recent trip away, for the first time since we’ve owned this place, it didn’t smell musty when we returned, so I reckon the Diathonite is offering a benefit already.

    Hope this answers your questions.
    Best wishes,

  3. Plastering Auckland - 8th May, 2020 Reply

    This is a short post showing videos and photos of the Diathonite being applied. It states about diathonite insulating thermactive lime plaster application and installation . Thanks for this amazing article. Great blog indeed, will visit again future to read more!! You must also check out it has some great insights too.

  4. Geoff Bolam - 13th May, 2020 Reply

    Hi Lois, Thanks for posting the article.
    I’m considering Diathonite for the conversion of a small church to a holiday let.
    We have similar problems of damp in the walls – caused by a modern concrete floor and damp-proof membrane, cement pointing, leaky gutting, no heating, etc.
    We were initially advised to dryline the entire building but this rejected on conservation grounds, and then to just remove the cement pointing and repoint and repair with lime.
    However, we’re going to have to work hard to heat the building as the roof cannot be insulated much either, so now looking at insulated plaster at it appears to offer a solution both issues.
    I’ve been looking at Diathonite but our architect is cautious about using a ‘modern’ material in a historic and about the longevity of it.
    I just wondered if you’d experienced any issues, such as cracking, performance, decorating etc, since having it installed?
    Thanks Geoff

    • LoisLogsLune - 13th May, 2020 Reply

      Hi Geoff,
      Thanks for your post. I think you’re doing the right thing in avoiding drylining – when we removed ours it was horribly mouldy behind, which can cause really bad indoor air quality, and aggravate conditions like asthma. Lime pointing will help too – it allows the stone to dry out quickly and won’t trap moisture.
      The Diathonite seems great for us so far – it’s been in for 12 months now. I think I’d struggle to describe Diathonite as “modern” – its main ingredients being lime (an ancient product!) and natural cork – you only need look to some of our historic buildings to find lime stands the test of time much better then cement. In terms of performance, we’ve not observed any cracking or damage beyond one or two spots of superficial cracking on our lime plaster top coat where it dried too fast, but we have no reason to suppose this goes into the diathonite layer, and we will remedy these when we get to decorating those areas. But there is no damage around, for example, the front door, which does vibrate a bit as it opens and closes – the diathonite is solid there. There is one area of diathonite which may need to be addressed – a small wall, around 1x1m seems to have lifted; we think this is because it was applied to smooth brick in that spot, and because access was especially awkward just there, we don’t think it got its spatter coat key. Elsewhere though it seems really solid.
      We used a lime and sand mix for the finishing plaster coat. There was some staining as we applied this, a darkish yellow/brown stain leaked through, and we think this was tannins from the cork, however it has faded back to the lovely soft warm grey of the lime plaster coat without any need for intervention. We’ve been advised that we should use breathable paint (avoid vinyl etc), and to keep the area of tiled finish to a minimum to ensure it performs as intended (I guess to manage any moisture loading from the outside). I think also we’ll have to put up a framed area to install the shower cubicle against the diathonite wall, but these sort of considerations are normal for managing an old building.
      To be honest, i really would struggle to fault it as a product. It was expensive as a material, but the installation cost was lower than for some other approaches because it was so fast for the installers to do the whole job. I’ll try and get some pictures posted up of the finished bits asap.
      Your project looks really exciting – good luck with it!

  5. Colin - 9th July, 2020 Reply

    Hi Lois,

    A great three posts on your application of Diathonite. Down here in Kent, we are about to embark on a retrofit of a Victorian house with solid brick walls – so similar enough to learn from your experiences, but also different enough that I can’t just apply them 1:1.

    My question though is related to drying time – specifically, how long did it take your 50mm application to dry? I can see from Diasen’s tech specs that they claim 15 day’s drying time, but I can’t see what thickness that relates to. The question we are asking ourselves is – how long do we have to wait from application (60mm Diathonite + Argacem HP) coat before we can paint the walls?

    Any insight you can share will be very welcome. Thanks,

    • LoisLogsLune - 12th August, 2020 Reply

      Hi Colin,
      Thanks for your great feedback.
      In relation to your question, my understanding is that the 15 days before the finish coat and then perhaps the same again before painting, providing that you are using a breathable paint. The products may continue to cure after this time, but assuming the condition is not too cold and that there is reasonable ventilation to avoid high humidity, it can continue to cure after the top coat and painting. A breathable paint is important not only to allow the product to finish curing properly, but to ensure that it can function as intended throughout it’s life – it will manage the moisture content of the walls by absorbing and releasing moisture according to the conditions, but only if there is no coating blocking this process.
      My own experience is probably irrelevant – since we’ve not yet painted any of the walls! We will leave most of them the natural colour. We also used a lime plaster top coat (lime and sand mix) instead of argacem on the basis of cost – I am preparing a post on this topic for publication later this year (when I have the time). The top coat was applied about 3 months after the diathonite, because we were doing other jobs in the meantime.
      Hope this helps!

  6. George Harris - 14th September, 2022 Reply

    Hi Lois,

    How’s your insulation performing?

    I’ve also got a wall covered in 0.037, but that was before I discovered the work of Nigel Copsey and David Wiggins. Wiggins and others research into NHL’s is shocking. Not only do they continue to strengthen over 1000 days (sometimes doubling their strength as compared to 91 days) but they also vary hugely in their actual strength, regardless of what the bag says.

    It’s getting on for 2 or more years since yours went on, so I’m hoping the NHL 5 in our insulation is actually a weak one, and is offset by the volume of other good bits to aid breathability/moisture movement in the plaster.

    PS. Can send a link or two if you’d like.

    • LoisLogsLune - 14th October, 2022 Reply

      Hi George, Thanks for your message. We’re very happy with the insulation thanks, although there are still unfinished elements of the retrofit so I can’t comment yet on the overall performance. I’d say though that in particular, in the bathroom (which has been completed and is used regularly as a bathroom so experiences high humidity, including through a couple of winters already) the external walls are performing nicely, and there are no signs of damp, which really is the primary consideration, followed by the job of limiting heat loss.
      I’m not familiar with the work of Copsey and Wiggins – i’d be happy to look at any relevant links – thanks.

      • George Harris - 7th November, 2022 Reply

        Hi Lois,

        Please have a look at
        For a presentation on the benefits of hot lime. There’s a section in the video about NHL‘s, but for a longer presentation about the why and how of hot lime vs NHL or cement;

        As I said, my co

  7. George Harris - 7th November, 2022 Reply

    (Dont know what happened there!) My concern is long term moisture movement.

    Sadly I don’t know why your reply didn’t get to me sooner, I didn’t get a notification about you having done so!


  8. Jon - 5th January, 2023 Reply

    Hi Lois,
    Great blog, thank you.
    What kind of ground floor did you eventually install, and how did you address the issue of thermal bridging at the interface of the ground floor with your new diathonite walls please?

    • LoisLogsLune - 6th January, 2023 Reply

      Hi Jon, Thanks for your message. We have had a bit of a work hiatus these last two years, so our ground floor remains unfinished! The plan though, is to lay overlay insulation and a floating floor on top of the existing slab. This will mean that there is no thermal bridge between the diathonite IWI and the floor. You can see this here .
      It’s actually more tricky on the walls which have had EWI, and those external walls which have become internal walls where we built the extension. Luckily for us, these are all below ground level, so never exposed to very low air temperatures, but moreover, we painstakingly insulated the perimeter down to the foundations on the outside, which should limit this effect.
      Hope this helps?

  9. Jon - 8th January, 2023 Reply

    Yes, very helpful!
    Do you know of any fellow researchers that would like a project to collect data from in relation to interstitial condensation and thermal bridging, Lois?
    If you do please email me their details.
    Many thanks,

    • LoisLogsLune - 11th January, 2023 Reply

      Hi Jon, Are you hoping to volunteer your project for data collection? If so, sadly no, i’m not aware of anybody – I would have loved to collect data on our project too, but it was a cost too far to buy data loggers and I didn’t know anybody to borrow them from at the time. Also for us, with all the other variables, largely uncontrolled by us actually inhabiting the building throughout the project (hours of occupants in the building, set temperature for heating, actual temperature, airtightness & insulation (improving as the build progresses), other moisture sources (e.g. drying plaster etc), and then of course the weather, it would have been next to impossible to single out causes of any trends in the data. It might prove to be too “noisy” for most researchers – but perhaps your project has fewer of these variables on the go?

  10. Jon - 19th January, 2023 Reply

    Hi again Lois, I’ve been doing a bit more research and a couple of things have come up that I’d be interested to know your thoughts on:
    1. Using a DPM in your floor may force moisture horizontally along the underside of the membrane and into your walls. I got this from advocates of Limecrete floors that use a geotextile membrane below recycled glass.
    2. NHLs (and Diathonite is using NHL 5!) not only have reduced porosity (compared to non-hydraulic lime plasters), but keep on hardening, so over time they act more like cement, trapping moisture, not allowing it to migrate out of the wall.
    Anybody got definitive answers to these two possibilities please?

    • LoisLogsLune - 31st January, 2023 Reply

      Hi Jon,
      Thanks for your follow up. In relation to 1, I think Yes, this is a very plausible outcome. However for us, we had a pre-existing concrete floor (guessing it’s between 20 and 60y old) with a liquid DPM applied. We’ve at no point had any intention of digging it up (effort, logistics, disruption, cost, embodied carbon, risk to the remaining structure). We also know that the footings have flowing groundwater, so water in the walls is highly likely anyway. Therefore, we’ve spent a lot of effort on drainage around the perimeter at the footings. We’ve also no major evidence of damp in the walls to date. Therefore, whilst I wouldn’t say it was the most suitable approach in all cases, on balance of evidence, we’ve decided this is the best approach here.
      RE 2; I have been told about risks with NHLs, but unfortunately, this was after we’d chosen the diathonite route, and i’ve not had the time to properly follow it up (it might be a slight case of head-in-the-sand/address it if it becomes a problem rather than spend time worrying about it?). In another comment there are some links from a George Harris which might give you some insight (although i’ve not yet seen the content)? Hope it’s useful.

  11. Richard Talbot - 30th January, 2023 Reply

    Hi Lois, we have a very similarly constructed property to you just a little further north. Couple of questions:

    Did you consider pro clima type membranes when discounting use of wool / stud-walls / woodfibre board and I assume you were looking at to be used in addition to diathonite?

    Do you have any knowledge whether hand applied diathonite is as effective as machine applied? Contractors seem impossibly busy and also we may not have budget to use professional – despite the speed of application being so attractive

    • LoisLogsLune - 31st January, 2023 Reply

      Hi Richard,
      Thanks for getting in touch. RE stud-insulation methods, Yes, I believe I did include proclima membranes, but it was not considered in combination with diathonite. The analysis was all done at 2015 prices, so likely a little higher these days.

      I’ve no factual knowledge on performance/method of application, but anecdotally, I’ve been told that hand-application presses the pores more closed, so less trapped air, versus machine applied which slightly aerates the mix. I couldn’t say one way or the other though. We have used hand application in certain areas, i.e. where we didn’t get it quite finished with the contractors, but it would be impossible to make an objective analysis of performance.

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