Plastering - Good Idea Leaflet from Wickes DIY

The use of Wickes One Coat gypsum based plaster for both repair work and wall finishing is described in this leaflet. The other product in the system may be used in combination with the plaster to ensure the best possible, longest lasting job.

Use Wickes One Coat to create a smooth, flat finish over brickwork, blockwork or other types of masonry. The background needs to be sound and not loose or crumbly. Wickes One Coat should not be used to plaster damp walls.

Tools Required:

• Gauging trowel
• Tape measure
• Brush
• Sponge float
• Darby or straight edge
• Bucket and mixing stick
• Plastering trowel (for applying plaster to walls)
• Hawk (for holding the plaster)
• Tin snips or hacksaw
• A spirit level.

Before You Start:

• The Wickes Plastering System uses flatness guides to achieve a flat plastering surface. These are fixed to the walls and then plastered over.

• You will need to calculate how much plaster you will require and how many Wickes Flatness Guides you will need. 25kg Wickes One Coat Plaster covers approximately 2.5m2 when applied with a thickness of 15mm. Wickes Flatness Guides are normally spaced no more than 900mm apart and run from the floor to the ceiling.

• If you have not plastered before, you may find it useful to have a practice on a hidden wall or in the garage out of sight. Plaster is remarkably 'sticky' and so some will always end up on the floor instead of the wall. 

• Do not be put off, practice does help and it is worthwhile putting down plastic sheeting where you are working.

Preparing the Wall

• Remove any contamination such as mould, oil, grease or paint from the wall.

• Brush down the surface of the wall to remove any loose particles and dust. See FIG. 1.

• If the wall is constructed from smooth materials, such as dense concrete, clay bricks or smooth textured blocks, then you will need to treat the wall with Wickes Plaster Bonding Agent before plastering. Allow Wickes Plaster Bonding Agent to dry fully to provide a 'key' that Wickes One Coat can stick to.

• For surfaces that already have an adequate 'key', simply dampen the wall surface slightly with a brush and clean cold water.

Cutting Wickes Plaster Flatness Guides

• Wickes Plaster Flatness Guides are simple to use and make achieving a flat surface a lot easier. Plan to space them 900mm apart (or less, to suit the length of straight edge you will use later), mounted vertically.

• Wickes Plaster Flatness Guides should be cut to the height of the wall using metal cutters or a hacksaw. Care should be taken as the cut ends are sharp - protective gloves are highly advisable. See FIG. 2.

Mixing

• Only mix as much plaster as you can use in about half an hour. Start off with around half a bag of plaster, you will find you can mix up more as your plastering skills improve. For specific jobs, such as fixing Wickes Plaster Flatness Guides, only mix enough plaster to do that particular job.

• Ensure Wickes One Coat plaster is situated and mixed as close to the working area as possible and ensure there is adequate ventilation when mixing. Wearing a mouth and nose mask is advisable when mixing plaster. If you have sensitive skin, gloves should be worn.

• Mix the plaster in a clean bucket using cold tap water. You should allow approximately 14 litres of water combined with 25kg of dry powder. Always put the water in the bucket first then the plaster.

• Mix the plaster using a strong stick (a piece of 21 x 44mm planed timber is ideal) to a good workable consistency. See FIG. 3 This will be when all the loose powder has been mixed in and the plaster has thickened just enough to form 'peaks' when you dip your trowel in and remove it.

NOTE: Rather than using the mixed plaster straight from a bucket place a 700 x 700mm board (a spot board) on top of a workbench and pour the plaster on to this. This prevents the need to bend down to reload the hawk.

Fixing Wickes Plaster Flatness Guides

• Mix enough Wickes One Coat plaster to fix the flatness guides.

• Apply a continuous 15mm thick vertical line of plaster approximately 200mm from the start of the wall.

• Firmly bed the first flatness guide into the plaster and make plumb to the desired finished plaster thickness using a spirit level. FIG. 5. Smooth off surplus plaster from the perforated edges of the flatness guide with a trowel. Repeat the process for the remaining guides ensuring that they are 900mm apart (or less, to comfortably accommodate the length of straight edge you will use later).

• To ensure that the finished wall is flat, make sure that the guides are uniformly positioned. See FIG. 6.

• Leave the guides to set - this will typically take between 11/2 and 2 hours.

External Corners

• These require protecting from knocks and bangs and therefore a Plaster Angle bead is used. These are fixed in a similar fashion to the flatness beads apart form the fact that only dabs of plaster are used and they require holding in place with galvanised plasterboard nails. FIG. 7 & 8.

• When fixing the beads ensure that they are fixed to give the same plaster depth as the flatness guides. Carefully use a trowel to clean off excess plaster without disturbing the position of the bead. FIG. 9 & 10. Leave the angle beads to set.

Applying Wickes One Coat Plaster

• Only apply Wickes One Coat plaster once the background has been suitably prepared and any flatness guides have been fixed and properly set.

• Applying plaster correctly involves using the correct 'wrist action' and ensuring that the angle of the trowel blade against the working surface remains the same. If the blade is to flat against the work surface then too much plaster is applied and there is a risk of the trowel 'sticking' to the plaster. Too steep an angle will apply too little plaster. The correct angle is around 45°. FIG. 11 & 12.

• Load your hawk with a reasonable amount of plaster using the gauging trowel. To load your plastering trowel hold it at right angle to the hawk and push it towards the plaster whilst tilting the hawk towards you and lifting the trowel slightly until sufficient material is on the trowel.

• Mix as much plaster as you need, at most as much as you can apply in about half an hour. Apply the plaster material in two coats with a plastering trowel and hawk to a recommended overall thickness of 10-20mm, or level with the flatness guides. Apply using a firm, easy pressure with a spreading, smoothing motion. Do not plaster level with the floor, leave a gap of 25-30mm, which will be covered when skirting boards are fitted.

• The gap is left to prevent dampness being drawn up into the plaster from the floor.

• The plaster is then immediately 'ruled off' to form a level surface using a straight edge or darby. FIG. 6. Rule the plaster vertically to start with following the flatness guides, starting at the bottom and working up, and then rule again with a side to side motion. FIG. 13.

• Minor hollows that appear can be filled and the surfaced re-flattened using either the trowel or by ruling again.

• Sponging should commence just as the material becomes slightly firm (this largely depends on the suction in the background). The purpose of sponging is to bring the finishing aggregate in the plaster to the surface, thus creating a smooth finish.

• In order to avoid hollows, ensure that a figure of eight motion is applied with the sponge, and that the sponge has been soaked thoroughly to avoid extracting moisture from the plaster.

• It may also be necessary to wet down the surface using a water brush to allow the finishing aggregate to form on the surface.

• When sponging is complete, carefully trowel the surface. A slight wetting down of the plaster surface may be necessary at this stage to avoid friction and reduce dragging. See FIG. 14 & 15.

• A final dry trowel is applied immediately after the initial trowelling until an even matt white finish is achieved.

• Clean tools with water if you have finished or if the plaster has started to set.

• Remember to dry any metal tools and lightly oil them if they are not going to be used again. Always clean off the oil before you start using the tools again.

• New plaster should be left until thoroughly dry prior to painting wallpapering. A minimum of three weeks is normally required.

Repair Plastering

• Many of the plastering jobs around the home do not require the whole wall to be plastered. Old plaster can fail in small areas through age or around doors or windows through movement and vibration.

• Plaster that has failed through age and is no longer bonded to the walls needs to be removed to leave a sound surface. For small areas the sound plaster at the sides will act as flatness guides when 'ruling off'. See FIG. 16 & 17.

• If the wall is constructed from smooth materials, such as dense concrete, clay bricks or smooth textured blocks, then you will need to treat the wall with Wickes Plaster Bonding Agent before plastering. Allow Wickes Plaster Bonding Agent to dry fully to provide a 'key' that Wickes One Coat can stick to. The plaster can then be applied as described previously. See FIG. 18.

• If the plaster has been damaged through movement the old plaster still needs to be removed and the Wickes Patch & Repair Mesh should be used. See FIG. 20. This reinforces the plaster and will prevent cracking in almost all situations except where the movement is very severe.

• To fix the mesh apply a layer of Wickes One Coat Plaster to half of the depth of plaster required. Cut the mesh to size and push this in place with a trowel so the plaster comes through the mesh. Allow this plaster to set and then plaster the remaining area. See FIG. 21, 22 & 23.

Hints & Tips

• A new trowel will need to be 'worked in'. To do this place the trowel face down on a smooth concrete surface and make figure of eight movements. This will take the corners off and sharpen the edges. 
WARNING: a well used plasterer's trowel will have very sharp edges

• Do not overload your trowel as this causes more plaster to go on to the floor than the wall

• Use the short side of the trowel for smaller areas

• It is possible to 'over work' plaster, which causes the surface to break up. Should this happen do not panic, Wickes One Coat Plaster is a forgiving product. Stop work, have a cup of tea and then splash a little water on the plaster and re-trowel gently.

• Don't mix too much plaster in one go. Mix what you can use in half an hour.

• Where you are working should be well ventilated, but try to avoid strong draughts and large temperature changes.