Why Combine Diathonite and Wood Fibre Insulation?
Renovating solid masonry or historic buildings often means walking a tightrope: improve thermal performance without trapping moisture or damaging the existing structure. Combining Diasen Diathonite insulating plaster with Steico wood fibre boards achieves exactly that, creating a breathable, capillary-active build-up that improves comfort year-round.
This article explains how the system works, why it suits traditional walls, and what benefits clients can expect in terms of energy, comfort and building health.
A Fully Breathable Insulation System
Both Diathonite and Steico wood fibre are vapour-open and hygroscopic. Diathonite is a lime-based insulating plaster that contains natural aggregates such as cork and clay, enabling it to absorb, store and redistribute moisture rather than sealing it into the wall. Wood fibre boards also buffer humidity and allow moisture to pass through the assembly rather than accumulate at the cold interface.
Together, they form a continuous, “breathing” internal wall system. Moisture that migrates from inside the room or from the existing masonry can be safely managed and dried out rather than condensing within impermeable layers. This dramatically reduces the risk of interstitial condensation, mould growth and frost damage in solid brick or stone walls.
Thermal Performance and Winter & Summer Comfort
From a thermal point of view, the combination of Diathonite and wood fibre gives more than just a better U-value. Diathonite provides a first insulating layer bonded directly to the masonry, reducing thermal bridges and adding thermal mass to the inner face of the wall. This helps even out temperature swings and makes rooms feel more stable and comfortable in winter.
The wood fibre layer provides additional insulation with low thermal conductivity and high specific heat capacity. That high heat capacity is crucial for summer comfort: it slows heat flow from outside to inside, delaying and reducing overheating. The result is a wall build-up that not only cuts heating demand in winter but also noticeably improves indoor conditions during hot weather, especially in lightweight upper floors and roof spaces.
Moisture Management and Building Health
Moisture management is where this system really stands apart from conventional internal wall insulation with foams or foil-backed boards. Diathonite, applied directly to the brick or stone, acts as a capillary-active “buffer” that draws moisture away from the masonry and redistributes it across a larger surface area where it can evaporate safely. This is particularly valuable in older buildings that may lack a damp-proof course or are exposed to driving rain.
Because the wood fibre boards are also vapour-permeable and hygroscopic, they do not form a tight vapour barrier in front of the Diathonite. Instead, moisture can move gradually through the build-up. When paired with a compatible lime finish plaster, the entire assembly works like a lung for the wall: it breathes, buffers humidity and helps keep the structure dry for clients, which translates into a healthier indoor climate and longer-lasting fabric.
Acoustic Comfort and Surface Quality
The benefits are not only thermal and hygrothermal. Diathonite products have good acoustic absorption properties and can be used to level irregular masonry substrates. This makes them ideal as a robust base coat in older properties where walls are rarely straight. Once the substrate is true, the wood fibre layer adds sound attenuation, helping reduce both airborne noise and, in some assemblies, impact sound transmission.
On top of the wood fibre, a lime-finish plaster provides a durable, crack-resistant, and mould-inhibiting surface that remains compatible with the underlying materials. The finished wall looks like any high-quality plastered surface, yet it hides a multi-functional build-up designed to improve comfort and fabric performance without relying on petrochemical foams.
Typical Build-Up and Practical Advantages
A typical internal build-up with this approach might look like:
Existing solid masonry (brick or stone)
Diathonite insulating plaster as a levelling and capillary-active base
Steico wood fibre insulation board, mechanically fixed
Lime-based finish plaster or compatible breathable skim
This sequence brings several practical advantages for installers and specifiers:
Diathonite can correct uneven walls and integrate services without resorting to cement renders.
Thermal bridges at reveals and junctions can be significantly reduced by wrapping with the same breathable materials.
The system is tolerant of residual construction moisture and minor water ingress, making it more forgiving in real-world retrofits than closed, vapour-tight systems.
When to Recommend This System
The Diathonite + wood fibre combination is powerful in the following scenarios:
Internal insulation of solid brick or stone walls, especially in heritage or character buildings.
Projects where preserving breathability and salt transport are essential for fabric conservation.
Homes that suffer from summer overheating or high indoor humidity.
Clients are looking for low-impact, mostly natural materials rather than synthetic foams.
This is a holistic comfort-and-conservation solution. It improves energy efficiency, enhances summer and winter comfort, and respects the way traditional buildings handle moisture – all while using materials that are largely natural and recyclable.