How to 2-coat plaster
Before we start to apply the product, it’s worth noting the important information on the bag. Down the side of the bag you’ll find a use-by date; make sure the plaster is in date, as after this date the plaster may not perform as it should in terms of workability or set times.
Before applying an undercoat plaster, in this case Thistle HardWall, it is important to check that the background is suitable by referring to our latest technical information and that any preparation has taken place. As part of the background preparation, all 2-coat plaster angle beads should be fixed in position using Thistle plaster, in this case, Thistle MultiFinish.
Once applied and lined in, the angle beads should be left to set before you start to apply Thistle HardWall.
When mixing the plaster, always add the powder to clean, cold water. Keep adding powder to the water and mix to the required consistency.
Using a stainless steel trowel, apply the first coat of plaster to the background.
You’ll notice that our undercoat plaster is grey, this is because of where the rock is mined; and it helps our demonstration of the different plaster layers.
Once the entire background has been covered, a second thin coat of plaster should be applied over the whole surface. Once the required thickness of plaster has been applied, the wall can be ruled off with a darby, serrated straight edge or feather edge. Any low or hollow spots that have been missed during the application process can be filled.
When you are not applying Thistle undercoat plaster to a wall with a window or door in it, a broad screed system can be used as demonstrated here. Apply the material vertically on the wall, making the screeds a trowel width and to the correct thickness. This process will be repeated on the opposite side of the wall. The area between the screeds can then be filled in with plaster before ruling off with a straight edge to produce a flat wall.
Where a long wall is being plastered the screeds should be set at a distance to suit the straight edge.
Once the wall is level, a spatula should be used to close and flatten the surface of the plaster. Once it has started to pick up, go over the surface with a devil float to provide a mechanical key for the finish coat plaster.
Now the plaster has set, we’re ready to mix and apply the finish coat plaster. Don’t forget to check the use-by date.
We’re using Thistle MultiFinish over the Thistle HardWall undercoat plaster, to achieve a flat, smooth surface.
The first coat of finish plaster is applied to the wall.
After allowing the first coat to take in, a second coat is applied to obtain a smooth finish.
A number of further trowel applications are needed to obtain the finish required..