Gypsum plaster finishing is rendering technique used by builders to smooth over wall surfaces before applying a final fresh coat of paint. Commonly referred to as Plaster of Paris and taking the form of a powder containing silica, the compound is mixed with water and applied in layers to indoor surfaces such as walls and ceilings. As gypsum plaster is lighter than cement or mortar, it is an ideal compound to complete the finer detail work of a rendering job. Gypsum plaster finishing is also called skimming or browning.
- Skill level:
Things you need
- Stirring Stick
- Plasterer's compound
- Spirit level
- Spot board
- Plasterer's trowel
- Hand board
- Plasterer's float (preferably stainless steel)
- Splash brush
- Plastic sheets (depending on job size)
- Ladder or plasterer's stilts
- Roller tray
Wear a mask and protective eyewear. Brush off existing surface dirt and smooth over the wall surface. Cover all tape marks and indentations. If the surface is Gyproc, a type of gypsum plasterboard, ensure that there are no gaps in the sheets. If there are, seal them up.
Seal off the room and ensure that the room is at the right temperature; 12.7 to 21.1 degrees C is optimal. Add water to the plaster compound to achieve the right consistency; it should look like a heavy pancake batter and is commonly called "mud." Dip the roller in the plaster and start rolling the walls in a straight up and down motion. Avoid dry spots.
Roll the surface until it's completely covered. If the finish is a final skim coat, a final layer in the plastering process, the surface coat should be no more than 1/8-inch thick.
Smooth over any bumps or imperfections on the job you have just finished, applying more compound as needed to do this. Spray with water areas which are drying too fast to avoid cracking. Roll and keep rolling until you have uniform coverage. Make sure that the surface is opaque and porous.
Let the surface sit overnight and then sand before priming. Paint after the right level of smoothness is achieved.
Tips and warnings
- When buying plaster, buy only what you need, as it has a short shelf life.
- Don't dispose of unused plaster down the sink, as it can plug up drains.
- Avoid overexposure to the plaster dust. Some variations of the compound contain silica or asbestos which may cause health problems if inhaled.
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