Project Details
Date: 2017
Location: Montech / Tarn-et-Garonne
Maitre d’ouvrage: Privé : Mr Gilles Mollard
Category: eco-renovation-houses

Project Description

This project was launched in early May 2017 in Montech (in the Tarn-et-Garonne department). The internal brick and stone walls of the building were stripped to remove the cement mortar covering. Our Tradical® Hempcrete insulating lining outdid itself as an easy-to-cast material, with a total wall surface area of 200 m² to cover for this project. The framework was installed in the morning and then shuttering was erected, infilled and removed in stages right up to the ceiling. Within only 24 hours, the first room was finished!


Restoring and insulating as a DIY builder

Interview with Mr Gilles Mollard, self-builder,
conducted in September by BCB


BCB: Can you describe the background to your renovation project?

GM: The idea was to renovate a traditional farm we had inherited. The farm is located in Montech, in the Tarn-et-Garonne department. There’s a large main farm building, with the same floor area of 100 m² on the ground floor and the first floor, which needed renovating. There’s also an 80 m² stable, which had already been renovated.

In terms of temperature, it gets very cold for about a week in winter with temperatures of between -7 to -10°C. Otherwise, average winter temperatures range between 1 to 5°C in the mornings, with warmer afternoons. In summer, the temperatures can rise up to 38°C. The range of summer and winter temperatures means we need high-performance insulation all year round.

The relatively poor state of the building made us decide to renovate it. The 30 to 40 cm thick rubble stone walls were in a bad state due to a high level of damp. The reason for this was that the building had been formerly renovated by coating the internal walls with a cement render. This didn’t prove to be ideal and it was then covered by a brick veneer. A smell of dampness permeated this family home. Living in it was impossible for us and we wondered how to improve the situation.

BCB: How did you discover hempcrete?

GM: A materials supplier, Point P, suggested the hemp-lime solution when we told him about the state of the building and our project. I then browsed the web for more information.

We wanted simple solutions that would suit our walls and insulate them. I really didn’t want to go for the conventional storey-high panel option, as our walls were neither straight nor flat. I looked at the different solutions with the idea that the walls should be able to breathe.


BCB: A two-stage renovation project

GM: The first thing we did was to let our walls breathe again by stripping them and coming back to how they were before the previous renovation work. We took the brick veneer and the cement off to reveal the underlying rubble stone. The second thing we did was to properly restore and insulate the walls.


BCB: Why did you choose to use hempcrete as an insulating lining?

GM: I wanted to apply insulation directly onto the walls to repair and insulate them at the same time. I quickly realised that we needed to avoid creating thermal bridges if we wanted the insulation to be really effective. So, we reconsidered how we were going to do the floors, for example, so that we could insulate continuously from ground floor to roof, without there being a gap where the ground floor walls met the first floor.


BCB: What made you decide to do all this work yourself?

GM: I didn’t know anything about using the materials we chose. And I’m not a professional builder. It was all completely new to me. What really made me decide to do it myself was the excellent support I received from your technical consultant.


BCB; What were the key points to remember for successfully completing the work?

GM: One of the important things was to create a layout plan for all the electrical conduits so that the sockets would be in the right places on the battens.

These battens, which were part of the insulating lining solution, form a light frame structure fastened to the walls and are very easy to install. There’s no hard and fast rule about them being properly aligned or straight. This is such an advantage when your substrate is old walls!

What I did spend time on was laser positioning the screw heads on the battens. The heads determine the flatness of the surface of the cast hempcrete. They act as spacers for placing shuttering panels at the right distance and also as guides for installing the power sockets.


BCB: Can you give us an idea of the timing for the work?

GM: All the preparation work was key to making it easier to cast the hempcrete insulating lining. I was really surprised at how easy it was to install the shuttering, fill the gap between the wall and the panels and then remove the shuttering. It only took half an hour for a whole length of shuttering panels! And the end result looked very good.

BCB: What was your time schedule for actually doing the work?

GM: The work started in May 2017 and we finished the ground floor in early July 2017. We only worked weekends when we were free.

If I add all the time spent working on the project, it comes out at about 12 days, working from 9 am until 4 pm, to complete the hempcrete insulating lining on the ground floor.


BCB: What’s your initial verdict on having chosen this ‘insulating lining’ solution?

Using a wet mix (hemp+lime+water) instead of dry solutions (fibres or wools) was not an issue. Hempcrete had the added benefit of enabling me to fill in defects in the walls at the same time as insulating them thanks to the thickness cast.


‘For me, hempcrete is masonry work that insulates too.’

When all is said and done, casting hempcrete is much faster than installing ceiling-high panels, for example, which requires accurately setting up a framework, installing the insulation, preparing the panels (joints, sanding, primer) and applying the finish. And in the end, is that kind of system really that breathable and durable?

As for Tradical® Hempcrete insulating lining, it’s easy to set up the framework, and the shuttering and infill system are fast to implement. And when it’s dry, you can apply a lime finish on it directly.

‘I’m also reassured by this material’s resistance to rodents, which is really important when you live in the countryside.’

BCB: Do you have any before-and-after impressions to share with us?

GM: Not for the moment as the work is very recent, but I can already see the benefits for the house. The pleasant smell of hempcrete is a welcome change from the damp smell we had before doing work on the house!

We’re not living in the house full time yet as there’s still work to be done. But when it’s cold and we go there, we’ve noticed that the atmosphere is more pleasant. There’s not that ‘cold wall effect’ feeling any more.


‘With just 10 cm of Tradical® Hempcrete, we achieved our objectives! In terms of acoustic performance for one of the bedrooms too, where all the walls are lined with hempcrete.

It’s an exceptional product.’


BCB: What finish are you planning to apply to the hempcrete?

GM: Hempcrete lining has a beautiful natural look and it seems a shame to cover it at all. But I think I’m going to cover it with a Tradical® Décor lime render after all, to protect it. It can be applied as a very thin coat, the texture is very easy to adjust and it complements the lining nicely. What more can a non-professional like me ask for?

Before applying the finish, we will have given the hempcrete plenty of time to dry as work on the house progresses.


What conclusions can you draw from your experience of using this unrivalled bio-based material?

GM: Overall, hempcrete is simple to use and apply. The spirit of our house has been left intact. The insulation offered by the material has already provided a feeling of comfort and the design freedom it also offers has given our house its old charm back.


‘Today, I feel relaxed. Now that the lime and hemp lining has been cast, I just have to finish the renders. The work we’ve done will last for years. What more could we want!



Montech project profile


  • Tradical® Hempcrete: Tradical® Thermo lime and Chanvribat®
    Thickness: 10 cm on average
  • Lime finishing render: Tradical®Décor

Environmental footprint
20 m3 of Tradical® Hempcrete = 5.7T of CO2 stored


Interested in learning more about Tradical®?

BCB Tradical®:

More examples of hempcrete homes

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