When finishing the concrete structures, the exteriors of the walls and the rooms will have a coat of plaster. The material is a paste formed by mixing cement and water in a given proportion. It adds to the strength of the structure when it sets. The evolution of plaster through the ages saw the use of two minds of material – gypsum and lime. Even today, these are in use to give beauty to the exteriors of concrete structures.
Setting of plaster
After we plaster a wall, we allow it to set. Setting is the process of hardening into a rock-like consistency through the removal of water and heat. The chemical process is crystallization and the plaster upon hydration, hardens.
This building construction material called plaster can have one of the three ingredients – lime, gypsum, or cement. This plaster in each case will act in the same way. Plaster has relatively low strength but is extremely workable. So, they use it to finish the exteriors.
The maximum thickness of the plaster on a vertical surface allowed is only ¾ inch. If you want a thickness more than that you must use steel framework to support the plaster.
Action of the plaster
Gypsum plaster has another name, plaster of Paris (POP). When you heat gypsum to around 300°F, it releases water as steam and becomes POP. When the powder combines with water molecules again, it turns back into gypsum.
One can use this plaster to get a variety of finishes to the concrete structure. These imitate wool, metal, stone, of even fabric and finds use mostly on movie sets to create special effects.
Advantages and disadvantages
This plaster has many advantages such as:
- Prevents conduction of heat, so we use it as a heat shield.
- Light, so you can build huge structures easily.
- This has enough strength to resist ordinary knocks.
- You can mould it to any desired shape.
- Possible to create artificial surfaces resembling wood or stone.
- Get smooth finish to walls.
- You can use paint on the finished surface as this does not interact with paint.
- Does not shrink when it sets.
The inherent disadvantages are:
- No strength, so cannot take up loads.
- Costs more, so cannot use extensively.
- Labour costs too will be more since working with this plaster needs more effort.
People gain more through this plaster
So, if you plaster a wall with gypsum it will prevent heat from escaping. This will cut the air-conditioning costs. Moreover, since the curing time is negligible, you can begin painting immediately upon plastering.
The other big advantage is the sound control because of the higher density of the plaster. Apartments and condominiums that use this plaster need to spend less on sound proofing. The good exterior finish of the walls makes the walls seem attractive.
The dense spread of the plaster helps keep the cold out and this will help in regions where the weather is cold. In addition, it keeps the vermin and insects out. All this adds up to the value of the property. In other words, you get more when you use this plaster.