Plastering is the application of wet mixes of fine cementing material and sand to the internal surfaces of the wall. It is primarily intended to provide a flat even surface to the wall. Rendering on the other hand is the application of wet mixes of fine cementing material and sand on the external surfaces of walls.
Rendering is usually more challenging than plastering because of its high degree of exposure that lead to problems such as cracking, inadequate adhesion, bond failures and crazing or hair cracks.
Method of application of plastering
Plastering should be applied from top downwards. The hawk and float method imply using the plastering trowel or steel float to collect the mortar from the hawk and pressing it on to the wall in sweeping stroke. This spreads the mortar in an almost even thickness.
Procedure for plastering and rendering
1. Clean the wall surface thoroughly.
2. Spray the background with water and apply cement slurry spatter dash.
3. Apply the first coat of plaster.
4. Roughen the first coat using a metal comb or lath scratches to provide a good key for the second coat.
5. Cure first coat for at least 48 hours.
6. Place plaster screeds at convenient distances to form guides for straightening the surface. Screeds are simply narrow bands of plastering mortar formed by bedding short pieces of lath in plaster dots. These dots are plumbed down and intermediate ones fixed. The spaces in-between the dots are then cemented with plastering material to form horizontal or vertical bands about 75 mm wide.
7. Flank-in the spaces between the screeds and rule-off with a straight-edge to a straight and even surface.
8. Use a wooden float to work the surface to a sandy gritty finish.
9. Clean up the working place.
Floor and wall tiling
Tiles are often used as interior finishes of walls, floors, water closets (WCs), bathrooms etc. The tiles are made of earthenware pressed in steel dies, fired in kilns and glazed during the second firing. Glazed tiles are usually from 6 mm to 10 mm thick and 100 mm square. The laying is done after the plastering coats have been applied. Since one of the major problems of tiling work is bond failure, the plaster should be left unsmoothed to provide adequate mechanical key.
The unglazed back of the tile is porous and absorbs water very fast. It is advisable to wet the background before application of tile. Tiles tend to be fragile and difficult to cut by manual means. The work must therefore, be carefully set out before commencing the fixing operation.
Procedure for floor and wall tiling
1. Hack the wall and clean thoroughly if surface is smooth.
2. Set out work starting from a corner making sure that all off pieces are placed at a corner at the base of the wall or floor.
3. Bed a flat piece of lath to a perfect level of the base of the wall to receive the first course of tiles. This may not be necessary with a finished tile.
4. Soak the tile in water.
5. Mix mortar 1 part of cement to 3 parts of sand. Fixing of tile nowadays is done with special mastics.
6. Spread the mortar on the tile bed and press, tapping it slightly into position. Ensure that the mortar or mastic covers the entire bed of the tile. The practice of dotting the tile bed with mortar or mastic should not be employed as it eventually leads to bond failure.
7. Level and apply a straight edge. By moving the face of the fingers over the edges of the newly fixed tiles, one can easily feel if the edges are flat to each other or not. Rub the joints flush with a piece of soft waste cloth.
8. Clean the tiles after setting and polish as a final operation.
9. Clean the tools and working area.
