Best Thin Internal Wall Insulation

The Best Thin Internal Wall Insulation for Cold Walls, Condensation & Black Mould

A high-density natural cork system trusted by Housing Associations, landlords and heritage buildings

• Cold external walls often require the best thin internal wall insulation to improve warmth and energy efficiency.
• Persistent condensation.
• Black mould returning every winter.
• Tenants reporting uninhabitable rooms.
• Surveyors issuing repeated warnings.
• Housing Associations fighting continuous call-outs.

This is the ongoing challenge across Britain’s older housing stock. These properties share one fundamental problem: the internal surface of the wall gets too cold, causing moist warm indoor air to condense on cold walls. Condensation feeds black mould. Unless the wall is insulated, the mould always returns.

This is where high-density natural cork insulation provides a proven, safe, compliant and permanent solution.

ECOPROCORK® have applied this system to Victorian terraces, 1930’s semi’s, mid-1800s farmhouses, solid-stone cottages, 1960s solid-wall flats, Abbeys, Manor houses and heritage buildings, consistently achieving excellent testimonials from occupiers, landlords and Housing Associations who report warmer rooms, no mould return and a dramatic improvement in comfort.

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Why Cork Is the Leading Thin Internal Insulation for Cold Walls

Cork is a natural thermal insulator with a cellular structure that warms the internal surface, stops condensation and allows the wall to breathe. Unlike foams, silicone systems, insulated plasterboard or anti-mould paints, cork solves the cause — not the symptoms.

Once the internal wall surface is warmer, condensation cannot form. Without condensation, black mould has no environment to regrow.

Cork works reliably in homes from the 1800s to the 1960s because it is:

• Vapour-open (breathable)
• Elastic and flexible for moving old walls
• Naturally anti-fungal
• Able to insulate at 4–8 mm thickness
• Environmentally safe and low-VOC
• Suitable for heritage and listed building guidance
• Ideal for occupied, moisture-sensitive spaces

This is why ECOPROCORK® systems continue to show perfect performance during annual revisits.

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Trowel or Spray — The Choice Is Yours

ECOPROCORK® offers two internal insulation methods:

1. Trowel-Applied Insulating Cork (TLICS™)
Ideal where spraying isn’t preferred, small rooms, tight spaces, heritage interiors or tenant-occupied homes. Applied at 4–5 mm and skimmed with plaster when dry.

2. Sprayed Internal Cork Insulation (SLICS™)
Perfect for uniform coverage, larger rooms, Housing Association mould programmes and irregular brick or stone walls. Applied at 4–8 mm and skimmed once dry.

Both systems deliver the same outcome:
a warm internal surface, no condensation and permanently mould-free walls.

Trowel or spray — the choice is yours.

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Technical Reassurance for Housing Associations and Retrofit Professionals

All technical performance, safety testing and product certifications referenced for our internal insulation systems relate to the Decoproyec® product range, which is fully tested, validated and CE-marked by the manufacturer.

ECOPROCORK® is the official UK distributor and technical training provider, supplying and installing these certified Decoproyec® products for internal insulation, mould remediation and heritage-safe refurbishment.

The Decoproyec® product range carries the following independently verified test results:

Vapour Permeability (Breathability)
Tested to EN ISO 7783, achieving Sd = 0.35 (Class I – vapour-permeable).
This confirms that Decoproyec® systems remain fully diffusion-open, supporting BS 5250 moisture control and PAS 2035 moisture-safe retrofit pathways.

Water Absorption & Waterproofing Behaviour
Validated under EN 1062-3 and UNE-EN 492, demonstrating low capillary absorption and a waterproof external surface while allowing internal vapour diffusion.
This ensures cold walls can dry safely while remaining protected.

Adhesion Strength
Tested to UNE-EN 1542, achieving 0.65 N/mm² adhesion.
This confirms compatibility with brick, stone, lime, plaster and render — essential for pre-1919 Housing Association stock and heritage buildings.

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Fire Behaviour
Fire performance tested to UNE-EN ISO 4589-2, with a result described as “practically incombustible.”
Under EN 13501-1, Decoproyec® products carry a Class E reaction-to-fire classification for internal use beneath plaster.
These are different tests but collectively provide strong reassurance of safe fire behaviour once the system is plaster-finished.

Elasticity and Flexibility
Measured under UNE-EN ISO 527-4, demonstrating 34.6% elongation and high tensile strength.
This ensures the system can tolerate the natural seasonal movement of older walls, lime structures and mixed-fabric Housing Association buildings.

Acoustic Performance
According to EN-29052-1, the system provides up to 19 dB sound reduction, improving comfort in flats and multi-occupancy housing.

VOC and Indoor Air Safety
The Decoproyec® product range contains no hazardous substances and is low-VOC, suitable for internal use in occupied dwellings, including vulnerable tenants.

Thermal Conductivity (λ)
The sprayed cork formulation tested shows λ = 0.050 W/m·K, with additional high-density cork formulations for internal insulation typically achieving 0.037–0.040 W/m·K.
Both values support meaningful thin-layer thermal performance for condensation control.

CE Marking
All Decoproyec® sprayed and trowelable cork products supplied via ECOPROCORK® are fully CE Marked by the manufacturer in accordance with European construction product regulations.

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These validated test results, held by the Decoproyec® product range, provide Housing Associations and retrofit teams with the reassurance that internal cork insulation is a safe, compliant, breathable and long-term solution for cold-wall condensation, black mould and moisture-sensitive solid-wall properties.

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R-Values & U-Values of Natural Cork (Validated Data)

High-density cork delivers measurable thermal performance at very thin layers.

R-Values

Thickness	R-Value
4 mm	~0.10 m²·K/W
6 mm	~0.16 m²·K/W
8 mm	~0.21 m²·K/W

U-Value Effects on Cold Walls

Wall Type	Existing U-Value	With 4–6 mm Cork
9″ solid brick	~2.00 W/m²K	~1.80–1.90 W/m²K
Solid stone	1.90–2.40 W/m²K	~1.75–2.20 W/m²K

This adjustment raises internal temperatures enough to prevent surface condensation — the key to stopping black mould permanently.

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Combatting Black Mould: Why Cork Is the Permanent Solution

Anti-mould paints, bleach cleaning, mechanical ventilation upgrades and cold-wall chemicals do not solve the root cause because they do not warm the wall. As long as the wall stays below dew point, moisture will form and mould will return.

Cork stops mould by:

• Raising the temperature of the internal surface
• Preventing condensation at the wall face
• Allowing moisture to pass safely through the structure
• Removing the cold, damp conditions mould needs

This is why every revisit — from terraced bedrooms to Abbey rooms — shows identical results: no mould returning.

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Go a Stage Further: Back-to-Brick with DECPROCAL Lime & Cork Basecoat

For walls that have been damaged by cement render, gypsum, damp, salts or decades of non-breathable coatings, a deeper approach is required.

DECPROCAL Lime & Cork Basecoat provides:

• Full vapour openness
• Salt resistance
• Deep breathability
• Thermal uplift
• A stable lime-cork substrate
• Conservation-friendly properties

This back-to-brick method is ideal for:

• Heritage and listed buildings
• Abbeys and historic estates
• Victorian terraces with gypsum failures
• Mid-1800s stone cottages
• Properties requiring full moisture safety

Once DECPROCAL has cured, an insulating cork layer (trowelled or sprayed) is added and finished with plaster, leaving a fully breathable, insulated internal wall.

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Why ECOPROCORK® Is the UK’s Leading Thin Internal Insulation System

Because it provides everything modern retrofit requires:

• Thin insulation for space-sensitive rooms
• Total breathability
• Permanent mould elimination
• Dew point shift for condensation control
• Fire-tested, CE-marked products
• PAS 2035 compatibility
• Heritage-safe, reversible materials
• Warm, comfortable internal environments
• Ideal for tenant-occupied homes
• Natural, sustainable and low-VOC
• Proven long-term results

Most importantly, ECOPROCORK® insulation works — and continues to work — in the real world.

Farm house testimonial.

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Become an ECOPROCORK® Approved Applicator

We provide:

• CITB-funded training
• Technical support
• PAS 2035 guidance
• Installation training (trowel or spray)
• Approved Applicator status
• Job referrals from national campaigns
• Full product and compliance documentation

Whether you trowel or spray, you deliver a system that makes cold rooms warm, safe and comfortable — permanently.

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