Skimming is a term used for applying a thin coat of plaster to a wall or ceiling to provide a smooth uniform surface. The plaster used is generally called ‘board finish’ and comes in a variety of pack sizes. The amount needed can be worked out by area/weight. 10kg should be sufficient to cover about 5 sq m at a thickness of 3mm. Only buy plaster when you need it, as the shelf life is minimal, and ensure it is kept in a dry room.
Preparation for skimming
Before starting, you should clear out the room and dust down the plasterboard. The idea is to get rid of as much dust as possible since, oddly enough, surfaces need to be kept as clean as possible. Dirt and dust can cause untold problems later and the short time spent cleaning up will pay dividends.
A useful tip is, when sweeping up sprinkle a little water on the area to be swept, this keeps the dust to a minimum.
- Spirit level
- Steel float
- Mixing utensils (as described)
- Hacksaw or tin snips
- Claw hammer
- Plasterers trowel
- A spot board (as described)
Taping the joints
The first job is to ‘tape’ all the joints. This helps with the integrity of the surface and reduces the risk of cracks along the joints between boards. Fortunately, there is now no need to use paper tape or hessian (scrim) on the joints. The latter was a messy job as it had to be stuck to the boards with plaster. There is now a self adhesive board joint tape which although more expensive, makes life a lot easier. It can simply be unrolled and stuck over the joints like masking tape. Butt join the tape rather than overlapping to avoid ‘bumps’ in the finish.
If you have a lot to do, a neat trick is to fit an old toilet roll holder to your belt to act as the tape dispenser. This leaves both hands free but, perhaps more importantly, keeps the tape clean – dust will stop it sticking to the boards.
Angle or plaster beads
Any external corners will need to have angle beads fitted to enable a sharp square corner to be produced. These are right angled, galvanised metal strips which have holes in the side fins for nails to go through for fixing. To cut them, simply measure and mark to length then use a pair of tin snips or a junior hacksaw.
The edges tend to be sharp so, wear work gloves and take care.
To fix in position place the spirit level on the corner to be beaded, if it is plumb nail the bead on using galvanised plaster board nails. Nailing up the bead in a uniformed manner keeps the bead square all the way up and down the corner. If the corner is out of plumb, hold the bead at the prominent part of the corner and nail at that point. Taking hold of the bead above, then below, use a spirit level to adjust before nailing in position. Make use of the spirit level’s straight edge to keep the bead in line.
Mixing the plaster
Using a plastic bucket, sprinkle a measured amount of plaster into the same amount of water and stir with a wooden stick or ladle. Stir until the mix is lump free and a smooth creamy consistency.
A hand whisk is a handy tool for this job.
When satisfied with the mix, sprinkle water onto the ‘spot board’ (a flat board, about a yard square placed at waist height on a suitable stable base). Tip the plaster onto the spot board.
Loading the float or trowel with plaster
It is a good idea to practice loading the float from the hawk whilst your stood over the spot board as this will catch any spare plaster.
Scoop up and load plaster onto the hawk. Now, holding the hawk in your left hand, if you’re right handed, (or visa versa, if you’re left handed) at a level between chest and shoulder, set the blade of the float at right angles to the bed of the hawk and push a measure of plaster towards the edge furthest away from you. As you do this, tilt the hawk slightly towards you and follow through with the float in a scooping motion. This movement is carried out in one fluid action. Practice this until you are satisfied with your progress.
Skimming the joints
When ready, the first job is to seal the joints by spreading a thin layer covering the joint tape. Hold the float at about 30degrees to the plasterboard and move it in a smooth upward motion, in line with the joint. Use enough plaster to allow the mesh of the tape to be left just visible. When you have completed all of the joints the plaster on the first joint will be dry enough to start skimming the boards.
Skimming the boards
Working from the floor level upwards, spread the plaster thinly (about 1/8″ thick) in vertical strips, stopping just short of the ceiling, then work downwards. Tuck the float into the corner at the ceiling and then work down to meet the upward sweep you have just spread. Keep clear of the taped joints on this first coat.
Applying the second or topcoat of plaster
When you have finished this first coat, you should be able to begin applying the second coat using long sweeping strokes to eliminate any ridges. Starting each sweep at the bottom corner of the wall and work along to make one continuous coating. After the wall has dried a little go over the wall with a clean float smoothing any marks or ridges, making sure to get all the way into the corners.
When the plaster has hardened (but not dried) “polish” it using a clean float. Use a wide paint brush to sparingly splash clean water on the surface as you go. This acts as a lubricant for the trowel and allows it to pick up a fine film of plaster which fills any minute holes.
If you wash your tools at regular intervals this will not only save your hands from becoming sore but will also turn out a better end product.