Your Monday home-study lesson: what plaster and render actually are, how every system works, and how we work on site. Then a quiz that marks itself.
Welcome aboard, Rylie! I can't be on site with you Monday, so today you're learning the trade from a screen instead of a scaffold. Work through every slide properly — everything in here is stuff you'll see, hear and use with us for the rest of the week.
Take notes as you go. The quiz at the end covers all of it.
This isn't just theory — the week you're with us we're doing a full silicone render job. Here's exactly what you'll see happen, in order.
George — the boss. Sunny — plasterer at G Green. Jamie — trainee plasterer, so he was in your shoes not long ago. Stick close, ask questions, keep the mixes coming.
We'll be working off scaffolding — you included, so the height rules in the safety module apply to you for real: ladder access only, stay inside the guardrails, keep the platform tidy. And it's going to be hot: bring water, and yes, you're going to need suncream 🤣. Rendering in the sun is no joke — for you or the render.
Coating internal walls and ceilings with a smooth, hard layer of plaster — turning rough brick, block or plasterboard into a flat surface ready for paint or wallpaper.
It's a finishing trade: our work is what the customer sees and touches every day. And plaster starts setting the moment it's mixed — there's no pause button.
The same craft applied to external walls — a tough, weatherproof coat that protects the brickwork and makes the house look sharp.
Render is the building's raincoat: it stops driving rain and frost getting into the wall and causing damp inside. This lesson covers all five systems we work with.
The most important module in this lesson. Every rule exists because someone, somewhere, got hurt. On a G Green site PPE goes on — no arguments, no exceptions.
The biggest health risk in our trade isn't falling — it's breathing. Cutting, mixing and sanding cement-based products releases silica dust. The damage (silicosis) builds over years and never heals.
FFP3
That's the mask rating you need — a cheap paper mask does not protect you. Damp down before sweeping, mix in ventilated space.
Wet cement and plaster are alkaline. Sitting on skin — inside a glove, in a boot, soaked into trousers — they cause chemical burns you often don't feel until the damage is done.
Cement is the worst offender — it can give a nasty burn if it's left on the skin. Never kneel in wet muck. Splash on skin? Rinse with clean water straight away. In the eye? Rinse 20 minutes and get it checked.
Bad lifting habits at 15 mean a broken-down back at 40. Plan the route first, bend your knees with your back straight, keep the load close, turn with your feet — never twist. Full plasterboard sheets are a two-person carry: asking for help is the smart move, not the weak one.
Falls are the biggest killer in UK construction. On your week you will be up on the scaffold with us, so these rules are yours: use the ladder access only — never climb the frame or the outside. Stay inside the guardrails, keep the platform tidy, and never drop or throw anything down. And if anything ever feels unsafe, on any site, ever: you say no and tell George.
A plasterer's tools are an extension of their hands. Learn the names — you'll be passing them to us all week.
| Tool | What it does |
|---|---|
| Finishing trowel | THE tool — flat steel blade for spreading and polishing plaster. Personal, worn in over years. Don't borrow one without asking! |
| Flexi trowel | A flexible steel trowel used for the finishing stages — the flex helps get that crisp, polished final finish. |
| Corner trowel | Shaped to run down internal and external angles — keeps the corners sharp and true. |
| Hawk | Square board, handle underneath. Holds a working load of plaster while the other hand trowels. |
| Bucket trowel | Short and stubby — scoops plaster from the bucket to the hawk. |
| Mixing drill & paddle | Whisks plaster to a smooth, lump-free cream. |
| Speed skim | Long blade dragged over fresh plaster — flattens a whole wall in a few passes. |
| Darby & feather edge | Long aluminium rules (the aerated feather edge is the lightweight one) for ruling render flat and true. |
| Hand float & power float | Float the basecoat up to an even, uniform surface once it's firmed. |
| Sponge float | Rubs up sand & cement render to an even texture. |
| Snips & beads | Angle beads make crisp corners; snips cut them to length. |
| Scarifier / scratch comb | Combs lines into the scratch coat so the next coat grips. |
| Splash brush | Big brush for flicking water onto the wall — dampening down, cleaning beads and helping the finish along. |
Internal plaster is made from gypsum — a soft, pale rock (calcium sulphate) dug out of the ground. The clever bit is what happens to the water inside it.
Mixing water back into the powder reverses what the factory did: the gypsum crystals re-form and lock together. That's why set plaster feels slightly warm — the reaction gives off heat. And it's why timing matters: once the crystals start locking, nothing stops them.
Retarders to slow the set so there's time to work it, and lightweight aggregates (like perlite or vermiculite) in backing plasters to add bulk and workability. Different recipes = different bags for different jobs.
| Plaster | What it's for |
|---|---|
| Multi-finish | The famous pink one. Thin skim (about 2mm, two coats) for the final smooth finish. Workable roughly 1.5 hours after mixing — then it sets whether you're ready or not. |
| Board finish | Skim coat designed specifically for plasterboard. |
| Bonding coat | Backing (undercoat) plaster for smooth, low-suction surfaces like concrete. Builds thickness to level a wall before the skim — and it's what we reach for when backing plaster is damaged and we need to patch in. |
| Hardwall | Backing plaster for masonry — brick and block. Tougher and more impact-resistant than bonding. |
Five ways to coat the outside of a house. Over the next slides we go through each one — what it's made of, how it goes on, and why a customer would pick it.
The traditional one — mixed on site, painted after.
One-coat, coloured all the way through, scraped finish.
Flexible coloured topcoat over a meshed basecoat.
Insulation boards on the outside of the house, rendered over.
System 5 is the finish family — sponge-floated, scraped, or textured — which we'll meet as we go.
Sharp plastering sand + Portland cement, mixed on site with water and a plasticiser (or lime) to make it workable and less brittle.
The mix is measured in parts: roughly 4 parts sand to 1 part cement for the first coat, slightly weaker for the top coat. Golden rule: each coat is never stronger than the one underneath, or it cracks.
Monocouche is French for "one coat". It comes ready-mixed in a bag — cement, lime, fine aggregates and colour pigment all the way through. Just add water.
Because the colour goes right through the material, it never needs painting — a scratch or chip shows the same colour underneath.
Applied thick — around 15mm, usually in two passes wet-on-wet, by hand or spray machine — then ruled off flat. Once it firms up ("goes green"), the surface is scraped back a couple of millimetres with a scraping tool, leaving a fine, even, matt texture.
That scrape is why it's also called scratch render.
A silicone-enhanced acrylic topcoat that comes ready-mixed in a tub, in almost any colour, with a fine grain in it (often 1.5mm) that creates the texture.
It's not applied straight to the wall — it's the top layer of a system: a levelling basecoat with fibreglass mesh bedded in, then a coloured primer, then the silicone finish floated to an even texture.
The silicone topcoat is only ~1.5mm thick — it follows every bump underneath it. So the whole job is won or lost in the basecoat. There are two types:
Loaded with polymers, so it's stickier, more flexible and stronger at a thinner build — around 6mm. Used where the substrate is already good and flat, or over insulation boards. Costs more per bag, needs less material.
Applied at around 10mm in two passes: first pass on, fibreglass mesh bedded into it while wet, then the second pass over the top. The extra thickness lets us pull a wavy old wall properly flat.
Finished with hand floats and a power float to an even, closed surface ready for the topcoat.
This is the skill you'll be watching all week. Flat isn't an accident — it's a sequence, and every pass has a name.
The basecoat then cures for several days — roughly one day per millimetre of thickness. Our 10mm basecoat means around a week and a half before the finish goes anywhere near it. Rush this and the topcoat fails.
Once cured, we come back: coloured primer on, then the silicone topcoat floated to its even texture. All those days of ruling, filling and floating are what make the final 1.5mm look perfect.
External Wall Insulation: rigid insulation boards fixed to the outside of the house, then rendered over — usually with the mesh basecoat and silicone finish from the last slide.
The boards are most often EPS (expanded polystyrene — light, cheap, great insulator) or mineral wool where fire performance and breathability matter.
Millions of older UK houses have solid walls — no cavity to fill with insulation. EWI is how you make those houses warm: it can dramatically cut heat loss and heating bills, stops cold spots and condensation, and the house gets a brand-new rendered look at the same time.
It's a growing part of the trade — energy prices have made it one of the most in-demand skills.
Six layers from brick to finish. This is the diagram to remember — it's the whole system in one picture.
When George quotes a job, this is the conversation with the customer — budget, look, and how much maintenance they want.
| System | Finish | Painted? | Stand-out point |
|---|---|---|---|
| Sand & cement | Sponge-floated | Yes — and repainted over the years | Cheapest; great for repairs & matching |
| Monocouche | Scraped ("scratch") | Never — coloured through | Clean modern look, low maintenance |
| Silicone thin-coat | Fine textured | Never — coloured topcoat | Flexible, breathable, self-cleaning |
| EWI + silicone | Fine textured | Never | Warm house + new look in one job |
Low down in every wall — usually a couple of brick courses above the ground — there's a damp proof course (DPC): a waterproof layer built into the wall that stops moisture from the ground soaking up through the bricks (called rising damp).
The golden rule: render must never bridge the DPC. If render runs from above the DPC down past it to the ground, it gives damp a path to climb straight past the barrier and into the house.
Remember from your job brief: full perimeter beading, no bell cast beads.
Before you render any house, you need to know what kind of wall you're looking at — because it changes what you're allowed to put on it.
One solid thickness of brick — about 9 inches — with no gap inside. These walls manage moisture by breathing: rain soaks in a little, then dries back out through the surface.
The trap: coat a solid wall in hard, non-breathable cement render and the moisture gets sealed in — it can't dry out, so it shows up inside as damp. Solid walls want lime render or a modern breathable alternative that lets the wall keep breathing.
Two skins of brick or block with a gap (cavity) between them, usually filled with insulation. The cavity is the moisture break: any rain that gets through the outer skin runs down the gap instead of reaching the inside.
That's why modern render systems work happily on cavity walls — the wall doesn't rely on breathing through its face the way a solid wall does.
Every day of your week will look different — one day it's hacking off the old render, the next it's beading and priming, then basecoating, and so on. But the shape of a day is always the same. All times are rough — the render decides the day, not the clock.
We work inside people's homes — that's a privilege, and it's also where the next job comes from: most of G Green's work is recommendations.
Watch these two videos.
Prep, PVA, both coats, flattening and trowelling up — the whole rhythm of a skim day.
Hack off, prime, beads, basecoat and mesh, ruling flat, floating up, then the silicone topcoat — exactly the job you're joining.
Below is a full silicone render job, start to finish — but the steps are jumbled up. Drag the steps into the right order using the ⣿ handle — or use the ▲ ▼ buttons, then hit Check my order. Green = right place, red = wrong place. Keep going until it's all green.
This is what George does before any job starts. Below is the front of a house that needs the full silicone system. Work through the four stages with a calculator — every answer checks itself. Type numbers only (no £ signs needed).
All measurements in metres. Rendered wall: 10.0m wide × 5.5m high. Six windows, each 2.4m wide × 1.2m high. One door, 1.0m wide × 2.0m high. The red dashed line is the DPC.
| Material | Covers / size | Average cost |
|---|---|---|
| Basecoat render | 1 bag covers 1 m² | £12 per bag |
| Bead adhesive | allow 2 bags for the beads | £12 per bag |
| PVC corner bead | 2.4m length | £3 each |
| PVC stop bead | 2.4m length | £3 each |
| Fibreglass mesh | 1 roll covers 50 m² | £20 per roll |
| Topcoat primer | 1 tub covers 100 m² | £40 per tub |
| Silicone topcoat | 1 tub covers 10 m² | £60 per tub |
41 questions covering everything you've just learned — marked as you go, with your score at the end. No notes. Be honest. We'll go through it together on Tuesday.