Purpose:
This standard measures the water vapor diffusion rate (permeability) of paints, varnishes, and coatings to assess their ability to allow water vapor to pass through.
Key Concept – Water Vapor Diffusion Factor (µ):
- The water vapor diffusion factor (µ) is a resistance factor indicating how much more resistant a coating is to water vapor diffusion compared to air.
- Higher µ value = More resistance to vapor (less permeable).
- Lower µ value = Less resistance to vapor (more permeable).
Simple Examples:
- Example 1: Highly Breathable Coating
- Material: Limewash paint.
- µ value: 20 (low resistance).
- Application: Ideal for walls requiring moisture breathability, such as historic buildings or damp environments.
- Example 2: Semi-Permeable Coating
- Material: Acrylic paint.
- µ value: 200 (moderate resistance).
- Application: Suitable for interior walls where some vapor permeability is acceptable but moisture protection is required.
- Example 3: Vapor Barrier Coating
- Material: Epoxy resin coating.
- µ value: 10,000 (high resistance).
- Application: Used in bathrooms or basements to block moisture completely.
If a 0.15 mm (0.00015 m) thick dry layer has an Sd value of 0.01 m, it means:
Key Values:
- Sd (Equivalent Air Layer Thickness): 0.01 m
- d (Material Thickness): 0.00015 m
- µ (Vapor Resistance Factor):
Using the formula:
Sd=μ×dSd = \mu \times d 0.01=μ×0.000150.01 = \mu \times 0.00015
Solving for µ:
μ=0.010.00015=66.67\mu = \frac{0.01}{0.00015} = 66.67
Result:
- The vapor resistance factor (µ) is approximately 67.
- This means the material is 67 times more resistant to vapor diffusion than still air.
Practical Meaning:
- Sd = 0.01 m indicates the material is highly breathable and allows water vapor to pass through easily.
- Such materials are often used in breathable coatings or paints for moisture-prone walls to prevent condensation buildup and mold growth.
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EN ISO 7783:2018 – “Paints and Varnishes – Determination of Water-Vapour Transmission Rate (Permeability) of Coatings”
What is Vapor Resistance Factor (µ)?
- The vapor resistance factor (µ) measures how resistant a material or coating is to water vapor diffusion compared to still air.
- µ = 1 means the material allows water vapor to pass through as easily as air (no resistance).
- Higher µ values indicate higher resistance to vapor diffusion, making the material less breathable.
Simple Examples:
- Example 1: Highly Breathable Material
- Material: Lime-based paint.
- µ Value: 10-20 (very low resistance).
- Application: Suitable for historic buildings or damp walls, allowing moisture to escape freely.
- Example 2: Moderately Breathable Material
- Material: Acrylic wall paint.
- µ Value: 150-300 (moderate resistance).
- Application: Used in living rooms or offices, where limited vapor resistance is required.
- Example 3: Vapor-Resistant Material
- Material: Epoxy coating or waterproof membrane.
- µ Value: 10,000+ (high resistance).
- Application: Ideal for bathrooms, kitchens, or basements where moisture protection is critical.
Key Takeaways:
- Low µ → High breathability (good for moisture escape).
- High µ → High resistance (acts as a moisture barrier).
- Used to select coatings for specific environmental conditions, ensuring proper moisture control and durability.
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Practical Use:
- Helps select coatings based on moisture control requirements.
- Ensures protection against dampness or mold growth in construction.
- Evaluates coatings for breathability versus barrier performance in different environments.
A vapor resistance of 50 meters means the material has the same resistance to water vapor diffusion as a 50-meter-thick layer of still air under the same conditions.
Explanation:
- Vapor resistance is often expressed in terms of equivalent air layer thickness (Sd), measured in meters (m).
- Sd = µ × d, where:
- µ = Vapor diffusion resistance factor of the material (relative to air).
- d = Thickness of the material (in meters).
In this case:
- An Sd = 50 m means the material behaves like 50 meters of still air in resisting water vapor diffusion.
Practical Meaning:
- 50 m vapor resistance indicates high resistance to vapor transmission.
- It acts as a vapor barrier, preventing moisture from passing through, suitable for moisture-sensitive areas like bathrooms, basements, or industrial floors.
Example Comparison:
- Highly Breathable Material (Sd = 0.1 m) – Allows vapor to pass easily, good for damp walls.
- Semi-Permeable Material (Sd = 1–5 m) – Moderately resists vapor, used in general walls.
- Vapor-Resistant Material (Sd = 50 m) – Strong barrier, ideal for wet rooms or waterproofing systems.
Let me know if you need further clarification!A vapor resistance of 50 meters means the material has the same resistance to water vapor diffusion as a 50-meter-thick layer of still air under the same conditions.
Explanation:
- Vapor resistance is often expressed in terms of equivalent air layer thickness (Sd), measured in meters (m).
- Sd = µ × d, where:
- µ = Vapor diffusion resistance factor of the material (relative to air).
- d = Thickness of the material (in meters).
In this case:
- An Sd = 50 m means the material behaves like 50 meters of still air in resisting water vapor diffusion.
Practical Meaning:
- 50 m vapor resistance indicates high resistance to vapor transmission.
- It acts as a vapor barrier, preventing moisture from passing through, suitable for moisture-sensitive areas like bathrooms, basements, or industrial floors.
Example Comparison:
- Highly Breathable Material (Sd = 0.1 m) – Allows vapor to pass easily, good for damp walls.
- Semi-Permeable Material (Sd = 1–5 m) – Moderately resists vapor, used in general walls.
- Vapor-Resistant Material (Sd = 50 m) – Strong barrier, ideal for wet rooms or waterproofing systems.
Let me know if you need further clarification!