Chapter 4: Finishing Materials PDF

Chapter 4: Finishing Materials 4.1. Importance of Finishes Surface finishes not only make products look nice, but they also ensure the product performance for long time. Moreover, finishes protect the products from outside damaging reactions, such as corrosion, wear and ru...

Chapter 4: Finishing Materials 4.1. Importance of Finishes Surface finishes not only make products look nice, but they also ensure the product performance for long time. Moreover, finishes protect the products from outside damaging reactions, such as corrosion, wear and rust. For example, the paint works as a protective film for the body of your car. If your car is left scratched for long time, this paint off area will likely be corroded and this eventually will damage your car body. Certain types of finishes, such as aerospace coatings, can influence the performance of the product itself. These coatingsguard the aircraft from weather resistance and sun destruction, ensuring its safety in the sky. 152/207  Chapter 4: Finishing Materials 4.1. Importance of Finishes Surface finishes not only make products look nice, but they also ensure the product performance for long time. Moreover, finishes protect the products from outside damaging reactions, such as corrosion, wear and rust. For example, the paint works as a protective film for the body of your car. If your car is left scratched for long time, this paint off area will likely be corroded and this eventually will damage your car body. Certain types of finishes, such as aerospace coatings, can influence the performance of the product itself. These coatings guard the aircraft from weather resistance and sun destruction, ensuring its safety in the sky. 4.2. Wall finishes 4.2.1.Plastering ($Jlaa) Plastering is a protective and decorative layer over walls or concrete surface to protect them against the atmospheric effect and give them nice appearance. The plaster is prepared by mixing sand and lime or cement concrete along with water. Plastering can be applied for various purposes. These include increasing the durability of the wall, decorating the structures of the walls, covering the uneven surface and rough walls, preventing water entrance into brick-work, and making a proper base ready for further painting works. > Requirement ofGood Plaster The surface of a good plaster should be smooth, non absorbent, not wash by water, and paintable. Moreover, good plaster should be firmly attached to the base surface, not shrink when it dries, fire resistant, and sound insulated. Plaster Defects and their Solution: If the plaster quality is not good enough it can cause one of the problems listed below. a. Plaster De-bonding Plaster de-bonding means that a plaster is disconnected from the wall. The reasons behind this phenomenon may be a thick plaster layer, insufficient substrate preparation or the use of dusty, oily or dry substrate. To avoid plaster de-bonding, we should remove any dusts or oils from the substrates, prepare the plaster in a good manner and finally add bonding chemical. 154/207 b. Cracks on Plastered Surface Cracks on plastered surfaces are very common problem that can be observed. Cracks are of different forms and due to different reasons. Crazing cracks are fine cracks like spider web. They happen because of the presence of excess fine content in the sand or due to dry wall on which plaster is applied, when the wall absorbs the water and fines gather on the surface, it leads to crazing. Separation cracks at joints occur at joints of two different materials because of differential thermal movement. Crack with Hollowness occurs due to hollowness in plaster because of extra water in the plaster mix or due to poor workmanship. c. Efflorescence on Plastered Surface When a newly built wall dries out, the soluble salts get out to the surface and appear as whitish 155/207 crystalline substances. This is called efflorescence. Efflorescence is formed on plasters when soluble salts exist in plaster itself or in one of the building materials such as bricks, sand, cement etc. It badly affects the adhesion of paints with the wall surface. To avoid this problem, all construction materials as well as plaster materials should be freefrom salt. d. Falling Out of Plaster Falling out of plaster from the plastered walls is of two types, flaking or peeling off. Flaking of plaster means that a small loose mass on the plastered surface is formed due to bad bonding between successive coats of plaster. Peeling off plaster means the formation of a patch in the plastered wall because plaster comes off from the surface. This is also because bond failure between successive coats of plaster. Both forms of falling out of plasters can be prevented by proper material selection, surface preparation and good workmanship. e. Popping of Plaster Popping is the formations of holes that break out of the plaster. It is produced due to the existence of contaminant particles such as burnt lime or other organic constituents in the mix of mortar. Removal of any contaminants from the mortar mix will prevent popping of plaster. 4.2.2.Pointing () Pointing is the finishing of mortar joints in brick or stone masonry construction. Pointing is the implementing of joints to a depth of 10 mm to 20 mm and filling it with better quality mortar in desired shape. It is done for cement mortar and lime mortar joints. Pointing finishing is applied to protect the exposed surface from adverse effects due to atmospheric action like rain, sun, wind and snow, or to enhance the appearance.Flush pointing is the most available type of pointing and is generally employed in brick masonry and stone masonry. In flush pointing, mortar is pushed into the gathered joints and joints are made flush with the edge of the stone or brick to provide a uniform appearance. After that, with the help of a trowel and straight edge, edges are precisely trimmed. This type of pointing doesn't have a good appearance,but it doesn't have any space for dust and water which make it long-lasting. Recessed Pointing is anotherform of pointing. It has a vertical pointing face and offers a better appearance. A recessed pointing mortar is pushed back inside the wall surface using a proper pointing tool. 158/207 4.2.3.Distempering (aa) Distemper is a water based paint in which the binding medium consists mainly of either glue or casein. The main ingredients of distemper are chalk, lime, water and some coloring agents if required. They are also known as cement paint; because it can be applied directly on cement walls without any other coating on them. The distempers are offered in powder form or paste form. They are to be mixed with hot water before use. As the water dries, the oil provides a hard washable surface. > Process of Distempering: The application of distemper is carried out in three successive steps (1) surface preparation, (2) prime coating and (3)distemper coating.  a. Surface preparation The surface to be distempered should be carefully rubbed and cleaned. The new plastered surfaces should be kept exposed for a period of two months or so to dry out before distemper is applied on them. If distemper is to be applied on previously distempered surfaces, the old distemper should be detached. b. Priming coating After preparing the surface, the surface is coated with priming coat is allowed dry. c. Distemper coating Normally twolayers of distemper are applied. The first layer should be light color and applied with great care. The second coat of distemper is applied after the first coat has dried and become hard. 4.2.4.Painting Paints are coatings of fluid materials which are applied as a final finish to surfaces like walls, wood and metal works. Painting is done to protect the surface from the effects of weathering, to prevent wood from decay and metal from corrosion, to provide a decorative finish. Painting process can be applied to new or old wood work, new or old iron and steel surfaces, galvanized iron surface, metals and plastered surfaces. For painting new wood surfaces the following steps should be followed (1) surface preparation, the surface to be painted should be clean, dry and free of dusts or spots, (2) knotting,knots in the wood surface must be killed or covered, (3) priming, applying a prime or a first coat on the wood surface to make the surface smooth, (4) stopping, in this step nail holes and cracks are filled using putty then the entire surface is rubbed with glass paper, (5) under coating, the process by which second and third coats are applied, and (6) finishing, applying the last coat on the wood surface.