Overcoming the effect of gravity can be challenging to the first-time plasterer. You must know how to prepare the surface, which tools to buy and what types of material to use during the two main stages of plastering. Although handling the various tools and mixing plaster to the right consistence is somewhat tricky, with a little practice, you will soon master the various techniques used by professional plasterers.
Brush surface dust and grit from the wall with a broom. Dilute two or three pints of PVA bonding liquid with water in a plastic bucket as directed on the printed instructions. Paint the mixture onto the wall with a 4-inch paintbrush or paint roller and let it dry. This will help the plaster stick to the surface and also prevent the material from drying out too quickly and causing surface cracks.
Prepare a plastic bucket filled with bonding plaster mixed with water. Add the powder to water and use a mixing paddle clamped into the chuck of a 1/2 inch two-speed power drill. Set the drill to the lower speed. Stir until all the lumps are removed and the plaster is mixed to the consistency of thick cake batter. Pour the mixture onto a piece of plywood supported between two trestles. Rinse the bucket and mixing paddle clean with fresh water.
Scoop a usable amount of plaster onto a metal plastering hawk. Place the long edge of an oblong plastering trowel on the surface and tip the hawk sideways. Load the trowel by scraping it quickly across the hawk.
Start at the top of the wall and work from left to right. Place the front edge of the trowel horizontally against the wall about a foot from the ceiling. Twist the trowel sideways to the vertical position while applying pressure between the loaded trowel and the wall. Start off at about a 30-degree angle; lower the front of the trowel gradually while sweeping the trowel sideways in a smooth continuous motion. Press the plaster into the surface by gradually closing the gap between the front edge of the trowel and the wall. The front edge should be about 10mm from the wall at the end of the sweep.
Go over the wall lightly in the other direction with the leading edge of the trowel held 10mm from the wall. You may have to go back and forth a couple of times before most of the trowel marks are off and the surface is fairly smooth. This will leave a three to five millimetre layer of plaster on the wall. Repeat until the top section of the wall is covered.
Smooth the entire first layer of plaster flat by applying moderate pressure while sweeping the trowel back and forth across the surface. Maintain a 10mm gap between the leading edge of the trowel and the plaster while doing so. This will remove the start/stop ridges left by the trowel. Aim for a fairly smooth flat finish and ignore minor trowel marks during this stage. Clean up the corners. Brush off excess plaster left on the ceiling and side walls with a dry three-inch paintbrush. Dress the plaster edges carefully with the trowel.
Start the first vertical layer about three feet below the horizontal layer of plaster. Work from left to right. Place the front edge of a loaded trowel horizontally against the wall and tip the trowel to about 30 degrees. Apply pressure and sweep the trowel upwards while squeezing plaster onto the wall by folding the trowel forward. Finish the upward sweep by smoothly rotating the trowel to leave a semi-circular overlapping layer across the bottom edge of the horizontal layer. Once again, the leading edge of the trowel should be about 10mm from the wall at the end of the sweep.
Smooth down with back and forth passes with the trowel. Repeat this across the width of the wall. Smooth any remaining trowel marks from the surface and dress the corners with the trowel and paint brush.
Plaster the lower half of the wall. Start at the floor or top edge of the skirting board if fitted, and work upwards and from left to right. Overlap the upper layer of plaster with the same semi-circular sweeping action. Smooth out trowel marks and dress the corners. Use a bucket filled with clean water to scrub the trowel and hawk clean. Allow enough time for the wall to dry a little. The surface must be firm but still damp to the touch before starting the next stage.
Go over the entire wall. Remove any remaining trowel marks or blemishes. Use either the same smoothing action with the trowel by applying firm pressure while sweeping the trowel across the surface, or brush out minor blemishes lightly but firmly with the three-inch paintbrush. If the surface is too dry, dip the tip of the paintbrush into water and flip the handle to sprinkle a few drops onto the surface. Be careful not wet enough the melt the surface plaster into a slurry.
Mix up a bucketful of finish plaster. Add powder to the water and mix with power drill and paddle. The finish plaster must be mixed to a thinner consistency than the bonding plaster—about the same thickness as firm pancake batter will do.
Plaster the final layer by starting with a horizontal line of plaster across the top of the wall and working downward in vertical passes until the entire surface is covered. The finish layer should be two to three millimetres thick. Use the same technique you have learned so far, but since the finish plaster is thinner than the bonding plaster, less trowel pressure is called for.
Wash your plastering tools and allow enough time for the plaster to dry until it has set fairly firmly but still damp to the touch. Smooth down the finish layer with the trowel and paint brush, using the same technique as before, but with less trowel pressure.
Examine the surface at an angle against the light frequently. If you detect hollows, add more plaster until the surface is perfectly flat. If there are obvious bulges, trowel flat with extra firm pressure. Carefully dress the edges and corners with the side of the trowel and a dry paintbrush.
Wash your trowel, hawk and plastic bucket clean after plastering the wall. Scrape any residue off the plywood mixing panel.