Rockwool between colombage vertical beams?

@hairbear has a good suggestion. Seems viable to mix the wool with plaster creates quite a ‘plastic’ filling which will take movement without cracking

For your walls can get the wool in panels that are quite easy to cut and then a thin coat of plaster, and paint. Nice musical video:


(Please note - plaster falling in coveralls if you use for ceiling work :face_in_clouds:)

History also recommends hairs in plaster, which seem to last at least a lifetime so I’d go with the wool

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Chanvre , ( not sure If it’s right spelling), is a great product to use for insulation between the wood. It’s easy to do yourself and plenty of suppliers in France. The artisan we got it from was very helpful, gave plenty of advice and came round to check all was ok after we’d completed the first wall, he also had examples of it used on walls like yours.


Thank you both - this is beginning to sound like a real possibility. :grin:

Its why we use polyfibres now as hair doesnt always last as any moisture and the lime begins breaking down the fine natural hairs.

I quite understand and defer to your knowledge


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Understood, one of the buildings I helped to improve with new lime plaster from the bad previous work.

Those sheep wool panels that chap was buttering look quite strong and dense compared to again rolls of insulation.


Oh what a wonderful job to have, :grin:

It was good, achieved so much until covid :sob:

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It’s a wonderful building. Been there many times, but not since I moved to France. It’s a pity it’s not on it’s original site, but that would cause quite an upheaval, and the loss of quite a lot of parking spaces :smile:

Not to mention flats. Sam Wanamaker wanted to build on the original site but couldnt raise the addition funds to buy up the site. They found the Rose theatre whilst excavating under the building opposite the original globe site.

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Hi… I apologise for a lengthy post! I am an advocate of hemp-lime! It was originally developed in France for precisely your purpose, to repair old earth/lime/debris infills between timber frames. It has the benefit when moist of being extremely sticky and easy to apply, helps to protect timber from attack, and when it has started to dry out, can readily be finished with a breathable lime plaster. A number of the other insulants suggested lack the same qualities, are “squidgy” and so less easy to finish effectively with a lime plaster (although almost anything is achievable with effort in buildings).
The dry resistance of hemp-lime (U value) does not convey all its qualities. It has inherent thermal mass and as a result slows the diurnal changes in temperature. The “shivs” of hemp are small conduits which trap water molecules in a complex process that also act as a form of heat store, operating in a slow transition over months, so when humid it operates significantly better than its dry resistance could predict. So much so, that when a supermarket was constructed with hempcrete panels, it had to show compliance with the building regs, so on that basis needed supplementary heating (in addition to the heat input from people, plant etc). In practice it was almost 1/3 more efficient than the calculations and needed little or no supplementary heating.
I have just bought precast dry hemp lime blocks from a local french supplier. (I could have cast my own – more below but did not have time before winter). These are produced under pressure in a mould. I am using these as an insulating, breathable walkable surface over newly laid timber boarding, with the particular advantage of being very resistant to combustion. These are easily cut by hand, and any residue/offcuts can be easily mixed with a little more lime and reused.


A few years ago I designed an eco-house in Leicestershire, with a timber frame stiffened by breathable structural sheeting internally. Externally the walls are mass hemplime, cast in-situ, with a lime external render finish. I suspect it is still reaching its optimal stable moisture level 4 years on, but it is heated by a single wood burner and comfortable in hot and cold weather, due to its thermal mass.


I also around that time took part in a hands-on applied research project, exploring the use of precast dry hemp lime panels (50mm thick) to replace old plaster in traditional buildings with an internal insulant, without changing the overall appearance or requiring frames, architraves or sockets to be changed. It was particularly intended for heritage buildings where the exteranal appearance should be retained unaltered, otherwise external wall insulation would be preferable! We tried passive drying outside, which worked but took some weeks, and the resulting panels were a bit friable and delicate. In my barn here in France I then tried the technique used by UKHempcrete of forcing air through a perforated panel (I used a small compressor, but bouncy castle type fans work as well). This produced biscuit hard dry panels in less than a week. We had panels tested for U value by an independent lab, but as noted above the performance is better than that indicates. We tested this on the exposed external rubble stone wall of an old cottage. Moisture levels in the wall had been over 90%, and the room was unreasonably cold all year as a result. We found that sirapit plaster repairs and bodges over the years had trapped the moisture, preventing drying out internally. (With climate change it is risky now to think walls will dry out adequately externally alone). We doubled its thermal performance with the 50mm layer of hemp lime. The room has since been comfortable and healthy.
(There is a brief description of its virtues, though not accurate on its history at Traditional and Historic buildings - UK Hempcrete )
Historic England publish about using hempcrete to insulate timber frames at
Some cast hemp lime block suppliers in France
Béton de chanvre en brique MULTICHANVRE de Vieille Matériaux | Alsabrico
Alliance 4 : Grossiste en chaux, chanvre et argile
Bloc de chanvre isohemp autoportant | Kenzaï Matériaux Écologiques


No need for apologies, your reply is very much appreciated. Sounds like an excellent idea. For the moment the lounge wall is the most important place to sort out, but there are lots of other places up in the loft where we still have earth/lime infills that are in a very poor condition. Now all I need to do is track down a supplier in Lot et Garonne. :grin:

If you are prepared to do it yourself, then local supplies are readily available. I recommend gloves when handling lime, but otherwise its a matter of picking it up in handfuls and shoving into place. A small concrete mixer is fine, and its wise not to make it too wet a mix. (Although the ideal mixers are those horizontal ones used for mixing up plaster for casting in ceramics workshops). For a finish you can make up and slap on by hand, or brush on, a limewash, one thin layer at a time to avoid cracking (at least four or five coats and it is translucent till dry). To avoid chalking people add things like skimmed milk (I have done this in the past to good effect).

My similarly enthusiastic artisan mason neighbour buys all his hemp shivs in plastic wrapped bales, together with lime from the local professional builders merchants - Pagot Savoie. I have bought slightly cheaper bales of hemp shivs (equally good for mulch in the garden) from garden suppliers such as Jardival. In our experiments (2014) we found no significant difference in outcome for the panels between using NHL lime (usually readily available from brico locally as NHL 3.5) and natural lime with added “pozzolan”. Pozzolans for Lime Mortars - Pat Gibbons (

In general a hemp-lime infill remains stuck to the timbers, so usually highly airtight and draft free.

I was struggling to remember the name of the supermarket, but it was M&S at Cheshire Oaks. “The in use heating energy use was considerably lower than anticipated in design and also when compared against the user specified benchmark. It is felt that this is due, in part, to the insulation of the Hempclad wall being better than expected, and also that the revolving doors reduced infiltration. In the discussion had during the final POE workshop it was stated that one of the reasons why the actual HVAC performance was better than predicted was because the hempcrete walls provided better than expected levels of insulation and a high level of thermal mass. This resulted in the building staying warmer in the winter and cooler in the summer when compared to the estimates made at design stage. For example, the BMS showed that the internal air temperature dropped by less than 1 °C when the external air temperature was 0°C over night. Other stores investigated lost on average 7 °C overnight for the same period.”
Building Performance Evaluation - Final report (


A great read, really enjoyed it. Did you experiment with NHL 2 in the hemp as it may move even more in response to the timber?
Jane Jones flagged up the hempcrete blocks for a forthcoming project to enclose what is a timber lean to garage space. Thanks for the other suppliers so I can connect with them.

@SuePJ. I highly recommend safety goggles as well as gloves, I dont know how but lime is a good shot at getting in the eyes.


I am glad it’s of interest! Yes, we did use NHL 2 as well when we tried the outdoor air-dried variants. It did not seem to make much difference, these remained a bit friable and fragile, although usable. (Welsh weather may have played a part). When I tried it internally in France, with air forced through a perforated ply base mould, mounted on a low berm, I brought some of our remaining brick dust pozzolan and natural lime from the UK. I could only easily get NHL 3.5 in the local area at the time (2014).
(The process was as thorough as we could make it at the time… so I used a high end thermal camera first. Then I laser scanned (Faro) the wall once the old plaster had been stripped off. Then a colleague took the scanned 3D data into a 3D digital model (BIM) and we then analysed both the predicted thermal performance, and the tiles to use without waste. The tiles were tee-gee at the edges, which complicated the moulds and detaching them again, although it worked. We pre-finished the panels with lime plaster too, so it was as dry a process as possible to fix indoors without dust and minimal wet trades. We used a thin natural lime mortar to glue them together and fix and fill to the wall. I then used a raspberry pi to capture the results of several thermal sensors and humidity sensors at intervals through the wall, outside and inside, at 5 minute intervals).
(edit: now I would use a cheap thermal attachment for a smart phone. and would be happy with the point cloud from similar cheap devices or even an i-phone. The 3D modelling and analysis remains a costly process, but I would start with Sketchup. There are only two hygrothermal software analysis packages that are rated. I have used WUFI but its expensive and not intuitive, you need training, so I would probably use intuition and judgement instead, and then measure - hence the raspberry pi and cheap sensors!).
The overall thermal conductivity (by a lab at Bangor Uni) was 0.09874 W·m-1·K-1. The original U value of the approx 400mm stone wall with internal plaster calculated as 1.55 w sq m deg C. The substitution of 50mm of hemp-lime panel improves it to approximately 0.8237 w sq m deg C.
We kept meaning to publish a paper on it, but never did. I would now go back and remeasure almost a decade on, and then seek to publish if I had time and opportunity!
For the pre-cast blocks I found a big range in prices quoted, and obtained several devis. The cheapest overall was 8 hours travel from us. Its difficult to assess the quality at that distance. In trying to buy local, I visited and finally negotiated our local Doubs manufacturer down to less than 100 euros more, but they amped up the TVA by insisting on shipping from their factory to a branch of Gedimat an hour in the other direction past us, who then delivered!

from our experimental cottage project:

the variance in colour is because there were different trial mixes.