Building Materials for Use in The Design of Low-Cost Housing

Building materials are the backbone of modern construction, and their quality and properties play a crucial role in the durability and aesthetics of structures. One such material that has been extensively studied and utilized over the years is wall plaster. This material, often overlooked, is essential for providing a smooth, durable surface for walls and ceilings. This article delves into the preparation of plaster bases, drawing from the comprehensive information provided in Circular No. 151 of the USA, titled “Wall Plaster: Its Ingredients, Preparation and Properties,” issued by the Bureau of Standards on January 9, 1924. The original compilation of this circular was a collaborative effort with the Bureau of Standards’ Plastering Conference in 1925. This article is the first in a series of three sections, each focusing on different aspects of wall plaster.

Plaster is a versatile building material that has been used for centuries. It is a mixture of water, lime, sand, and other additives that hardens to form a durable surface. The primary function of plaster is to provide a smooth, even surface on walls and ceilings, which can then be painted or decorated. However, plaster also serves other important functions, such as providing thermal insulation, soundproofing, and fire resistance. The quality of plaster is determined by the ingredients used and the method of preparation. Understanding these factors is essential for anyone involved in construction or renovation projects.

The preparation of plaster bases begins with the selection of high-quality ingredients. The primary components of wall plaster are lime, sand, and water. Lime acts as the binding agent, while sand provides the necessary bulk and texture. The quality of these ingredients directly affects the performance of the plaster. For instance, lime should be pure and free from impurities, while sand should be fine and well-graded to ensure a smooth finish. In addition to these basic ingredients, various additives can be incorporated to enhance the properties of the plaster. These additives may include fibers for increased strength, pigments for color, and retarders to control the setting time.

The preparation of plaster bases is a meticulous process that requires careful attention to detail. The first step involves mixing the dry ingredients thoroughly to ensure a uniform blend. This is typically done using a mechanical mixer to achieve a consistent texture. Once the dry ingredients are well-mixed, water is gradually added to form a smooth, workable paste. The consistency of the plaster is critical, as it affects the ease of application and the final finish. The plaster should be neither too thick nor too thin. After mixing, the plaster is allowed to rest for a short period to allow the ingredients to fully hydrate. This resting period, known as “slaking,” is essential for achieving the desired properties of the plaster.

The application of plaster is an art that requires skill and experience. The plaster is applied in layers, starting with a base coat followed by one or more finishing coats. The base coat, also known as the “scratch coat,” is applied to the wall surface and then scored to create a rough texture. This texture provides a key for the subsequent layers of plaster. The finishing coats are applied to achieve the desired smoothness and texture. The final coat, known as the “skim coat,” is applied thinly to provide a polished surface. Proper finishing techniques are essential for achieving a high-quality finish. This includes using the right tools and consistently applying the plaster.

The properties of wall plaster are influenced by the ingredients used and the method of preparation. High-quality plaster should be durable, resistant to moisture, and able to withstand normal wear and tear. It should also provide good adhesion to the underlying surface and be easy to apply. The performance of plaster is often evaluated based on its strength, flexibility, and resistance to cracking. Properly prepared plaster should be able to withstand minor impacts and resist cracking due to movement in the underlying structure. Additionally, plaster should provide good thermal and acoustic insulation, contributing to the overall comfort of the building.

In conclusion, wall plaster is a critical building material that requires careful preparation and application to achieve the desired results. The information provided in Circular No. 151, issued by the Bureau of Standards, offers valuable insights into the ingredients, preparation, and properties of wall plaster. By understanding these factors, construction professionals can ensure that the plaster used in their projects meets the highest standards of quality and performance. Properly prepared and applied plaster not only enhances the aesthetic appeal of a building but also contributes to its durability and functionality.

For further reading and detailed information on the preparation and properties of wall plaster, please refer to the following resources: