What binder does lime plaster use and how does it affect its properties?

What binder does lime plaster use and how does it affect its properties?

• A. Portland cement binder
• B. Lime binder; more flexible and breathable
• C. Gypsum binder
• D. Epoxy binder

Answer: (B)

Lime plaster uses a lime binder, which sets by carbonation rather than rapid hydration. That carbonating reaction gradually turns lime into a solid matrix that remains porous, allowing moisture to move through the plaster and the wall. This breathing quality is a hallmark of lime plaster and is essential for historic masonry, helping to manage moisture and prevent trapped damp. Because lime binders are relatively elastic compared to cement, lime plaster stays more flexible. This flexibility helps accommodate minor movements in the wall without forming large cracks, especially in older structures where movement and moisture changes are common. The slow, bedded cure also means the plaster develops strength over a longer period, closely matching the behavior of the surrounding masonry. In contrast, binders like Portland cement produce a hard, rigid, and less breathable layer that can trap moisture and crack with movement. Gypsum binders set quickly and are brittle, typically used for interior applications with low moisture. Epoxy binders are synthetic and not breathable, making them unsuitable for traditional lime plaster.

Lime plaster uses a lime binder, which sets by carbonation rather than rapid hydration. That carbonating reaction gradually turns lime into a solid matrix that remains porous, allowing moisture to move through the plaster and the wall. This breathing quality is a hallmark of lime plaster and is essential for historic masonry, helping to manage moisture and prevent trapped damp.

Because lime binders are relatively elastic compared to cement, lime plaster stays more flexible. This flexibility helps accommodate minor movements in the wall without forming large cracks, especially in older structures where movement and moisture changes are common. The slow, bedded cure also means the plaster develops strength over a longer period, closely matching the behavior of the surrounding masonry.

In contrast, binders like Portland cement produce a hard, rigid, and less breathable layer that can trap moisture and crack with movement. Gypsum binders set quickly and are brittle, typically used for interior applications with low moisture. Epoxy binders are synthetic and not breathable, making them unsuitable for traditional lime plaster.