There are two most common materials used in plastering - gypsum and lime plasters. Lime plaster was widely used in most plasterworks during the 19th century. Lime plaster is typically made out of lime, fiber, aggregate and water. Lime is usually derived from oyster shells and lime stones while hog or cattle hair is the fiber component used in the plaster mix.
Developments and changes in the construction industry have led to the gradual shift to gypsum plaster mix especially during the early parts of the 20th century. Plasterers soon came up a composite material made out of the combination of lime and gypsum plasters although, eventually, gypsum became the more popular plaster material.
Most of the buildings and homes that were built during the 19th century have used plastering mix made by combining quick lime with water. Lime, which is a hydrate product, easily absorbs water. This powder compound releases heat the moment it makes contact with water. The mixing process is complete as soon as heat is released and the lime putty that is derived from this mixing procedure is used as plaster material.
Fiber material is usually added to the lime plaster in order to get a coarse plaster and this type of plastering material is usually applied in two layers on the masonry in order to achieve the desired thickness. In most cases, plasterers apply three coats of the lime plaster. The first two layers are of the coarse material is known as the brown and scratch coat while the final coat serves as the setting stuff.
This final layer of the plasterwork uses a plaster mix that has a higher amount of lime putty and lesser amount of aggregate. Further, the plaster mix does not contain any fiber in order to attain a fine and smooth finish.
The initial two coats of plaster material are 3/8 inch in thickness while the finishing plaster coat is about 1/8 inch in thickness. There are instances where plasterers use additives such as whitish sand and marble dust to attain a specific finish and texture. In order to reduce the setting time of the final coat, plasterers add plaster of Paris to the plastering material.
It was during the 1900s when gypsum was first used as material for plastering. One of the distinct features of gypsum is that it instantly starts to cure as soon as water is mixed with the material. Gypsum immediately sets in a few minutes and the drying process is completed in a couple of weeks. However, for the untrained eye, it is difficult to distinguish gypsum plaster from lime plaster. Gypsum is acknowledged to be more rigid compared to lime and with this plaster material, there won’t be a need for fibrous binder.
Notwithstanding all of these distinct advantages of the plastering material, gypsum is prone to damage when exposed to moisture and damp conditions. Thus, lime plaster is more appropriate as plaster coating for masonry and when doing external plastering jobs.
To discover more about courses in plastering then more information can be found by selecting the following link: plastering courses
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