Why is 'fab' cloth used in mastic job?

• A. To prevent cracking after material dries
• B. To increase adhesion
• C. To improve thermal performance
• D. To speed cure

Answer: (A)

Fabric cloth in a mastic job acts as reinforcement that holds the material together as it dries. As the mastic cures, it tends to shrink and develop tensile stresses, especially at joints. The embedded fabric provides a mesh that carries part of those stresses and bridges small cracks, preventing them from propagating into larger ones. This keeps the seal flexible and durable under movement and temperature changes. It’s not primarily about sticking things better, speeding up the cure, or changing insulation performance—the cloth’s main role is crack resistance through reinforcement.