Learning how to plaster a wall is mostly about preparation and timing. The mixing is simple, the trowel work is not, and the material will set whether or not you are ready. Work in small sections and you will get a far better result than trying to do a whole room at once.
This guide covers the general method for any masonry wall, the tools you actually need, and the mistakes that ruin most first attempts.
Tools and materials you need
Tools
- Steel plastering trowel, the main tool for laying on and finishing
- Hawk, to carry mortar to the wall
- Plastic or wooden float, for flattening and closing the surface
- Straight edge or darby, about 1.2m, for ruling off level
- Scratcher or nail comb, to key the first coat
- Mixing tub and a paddle mixer on a drill, or a wheelbarrow and spade
- Bucket, brush and a spray bottle for water control
- Corner beads and tin snips for external corners
Materials
- Cement and washed plaster sand, never general building sand
- Bonding agent for smooth or previously painted surfaces
- Clean water
Sand grade is the material decision that matters most. Our page on plastering sand explains what to ask for at the yard and how much to order.
How to plaster a wall step by step
Step 1: Prepare the wall
Remove anything loose. Brush off dust, scrape old paint that is flaking, and rake out mortar joints slightly to give the plaster something to grip. Fill deep holes first and let them set.
Damp the wall down with a brush or spray bottle just before you start. A dry, thirsty wall pulls water out of your mix and you lose workability in minutes.
Step 2: Mix
Use 1 part cement to 5 parts plaster sand for internal work, or 1 to 4.5 externally, which is what SANS 2001-EM1 specifies. Mix dry first, then add water gradually until the mortar holds its shape on the trowel without sliding off.
Mix only what you can use in about 30 to 45 minutes. Retempering a stiffening batch with extra water weakens it badly.
Step 3: Set beads and guides
Fix corner beads to external corners on dabs of mortar and check them plumb. On large walls, run vertical screeds of mortar as depth guides so you have something to rule off against.
Step 4: Scratch coat
Load the hawk, take a trowel-full, and press it onto the wall at a shallow angle working upward. Aim for 10 to 12mm. Cover a section, rule it roughly flat with the straight edge, then key the whole surface with the scratcher.
Let it firm up. Depending on weather, that can be a few hours or overnight.
Step 5: Finish coat
Damp the scratch coat, then apply a finer mix at 5 to 8mm. Rule off flat with the straight edge, working diagonally to catch high spots.
Let it go from wet to firm, then float it in circles to close the surface. Finally, trowel it with the steel trowel and a light spray of water until it is smooth. Trowel too early and you drag it; too late and it will not close. Mix ratios and workmanship standards are published by the NHBRC.
Step 6: Cure it
Mist the wall daily for three to five days, especially in summer. Cement gains strength through hydration, not evaporation, and plaster that dries fast cracks.
Common mistakes when plastering a wall
- Mixing too much at once and racing the set
- Using building sand, which cracks and stains
- Skipping the bonding agent on smooth or painted surfaces
- Laying on one thick coat instead of two, which slumps and cracks
- Trowelling too early, which pulls the surface open
- No curing, the single biggest cause of hairline crazing
- Painting within a week, which traps moisture and peels
If cracks do appear later, our wall crack repair guide helps you work out whether they are cosmetic or something worse.
What it costs and when to call a pro
Doing it yourself saves the labour component, which is roughly R85 to R130 per square metre for both coats. A professional all-in rate is R90 to R160 per square metre internally.
On a small patch the saving is modest and the risk is low. On a full room the saving looks large until you factor in the cost of stripping off a failed attempt and paying someone to redo it.
Hire a plasterer when the job involves any of these.
- Ceilings, which are hard, heavy work and show every flaw
- External walls, where failure means water in the building
- Large areas that need to read flat across a whole room
- Walls you will paint in satin or gloss, which highlight every ripple
- Anything requiring scaffolding
For a substrate-specific method, read how to plaster a brick wall. For the mix in more depth, see how to plaster a wall with cement. To price the alternative, our plastering prices per m2 guide has worked examples.
If you would rather not, take a look at our brickwork and plastering service or ask for a free assessment. There is no call-out fee.
Frequently asked questions
How do you plaster a wall for the first time?
Prepare the wall by removing loose material and damping it down, mix 1 part cement to 5 parts plaster sand, apply a 10 to 12mm scratch coat and key it, let it firm, then apply a 5 to 8mm finish coat. Rule it flat, float it, trowel it smooth, and mist it daily for three to five days.
What tools do I need to plaster a wall?
A steel plastering trowel, a hawk to carry mortar, a plastic or wooden float, a 1.2m straight edge for ruling off, a scratcher to key the first coat, a mixing tub with a paddle mixer or a wheelbarrow, a spray bottle, and corner beads with tin snips for external corners.
How thick should plaster be on a wall?
Internal walls are normally finished at 12 to 15mm total: a scratch coat of 10 to 12mm followed by a finish coat of 5 to 8mm. External walls run thicker at 15 to 20mm. One thick application instead of two coats tends to slump and crack, which is why the two-coat system is standard.
What are the most common plastering mistakes?
Mixing more than you can use in 30 to 45 minutes, using building sand instead of washed plaster sand, skipping a bonding agent on smooth or painted surfaces, applying one thick coat instead of two, trowelling before the surface has firmed, and not curing. Painting within a week is another costly one.
Is it cheaper to plaster a wall yourself?
You save the labour element, roughly R85 to R130 per square metre for both coats, against a professional all-in rate of R90 to R160. On a small patch that is a fair trade. On a whole room the saving disappears fast if the finish fails and someone has to strip it back and start again.