Thistle HardWall backing plaster is first choice for plasterers working with medium to high suction backgrounds.

Thistle HardWall is a gypsum-based undercoat plaster designed for use on a variety of masonry substrates, providing a strong, robust base for finish plasters. It is typically used for medium to high suction backgrounds like brick or blockwork. Here’s a detailed overview of Thistle HardWall, its applications, and some key tips for proper use.

Key Features of Thistle HardWall

• High Coverage: Thistle HardWall offers good coverage, making it an economical choice for large areas. It is typically applied at a thickness of around 11 mm to 25 mm.
• Suitable for Masonry Substrates: This plaster is suitable for most masonry backgrounds, such as bricks and medium-density blocks, making it a versatile option for various projects.
• High Impact Resistance: The plaster provides strong, durable undercoat that can withstand significant impact, making it ideal for heavy-use areas.
• Rapid Drying: It dries more quickly than traditional undercoat plasters, allowing for faster finishing.

Application Process

When applying Thistle HardWall, it is essential to prepare the background properly to ensure the best adhesion and a smooth finish:

1. Prepare the Surface: Before applying Thistle HardWall, ensure that the background is clean, dry, and free from any dust, loose material, or grease. If the background is very dry or high suction, use a suitable primer like Thistle GypPrime to control suction and improve bonding​.
2. Mixing the Plaster: Add the plaster to clean, fresh water (never the other way around) and mix thoroughly until smooth and free of lumps. Follow the manufacturer’s recommendations for water-to-plaster ratio to achieve the right consistency.
3. Applying the Plaster:
   • Apply the first coat of Thistle HardWall to a uniform thickness of around 11 mm.
   • Use a hawk and trowel to ensure even application and a smooth finish.
   • If needed, a second coat can be applied to achieve the desired thickness (up to 25 mm).
4. Trowelling and Finishing:
   • Once the plaster begins to firm up, use a trowel to smooth and level the surface.
   • Depending on site conditions, the plaster can be floated for a finer finish or left rough for a key to receive a finish coat, such as Thistle MultiFinish​​.
5. Drying Time: Drying time for Thistle HardWall depends on ambient conditions, but it typically dries within a few hours. However, the final drying will take longer if the background has higher suction or in cooler environments.

Practical Tips

• Priming High-Suction Backgrounds: For high-suction backgrounds such as lightweight blocks, apply a suction control primer (like Thistle GypPrime) to reduce the rate of moisture absorption, ensuring proper adhesion of the plaster​.
• Avoid Over-Mixing: Over-mixing can lead to air bubbles and weaken the plaster. Aim for a smooth, lump-free consistency without introducing too much air.
• Consider Environmental Factors: Be aware that colder environments may extend drying times, and higher humidity may slow the plaster's setting. Always ensure the work area is adequately ventilated to allow the plaster to dry correctly​.

Conclusion

Thistle HardWall is an excellent choice for undercoat plastering on masonry surfaces. It offers versatility, strength, and durability, making it ideal for both domestic and commercial projects. When applied correctly and paired with appropriate finish plasters like Thistle MultiFinish, Thistle HardWall provides a strong, smooth surface ready for painting or decorating.

For more detailed guidance and additional products, visit the British Gypsum website or consult their comprehensive installation guides​​.