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Understanding Plaster Types and Coverage
Choosing the right plaster is essential for a professional finish. In the UK, plastering typically involves two layers: an undercoat and a finishing (skim) coat. The undercoat provides thickness and flatness, while the skim creates the smooth, paintable surface everyone wants.
The most common system used by professional plasterers is bonding coat plus skim. Bonding plaster is applied to walls at around 8mm thickness, allowed to set and be scored (scratched) to create a key, then a 2mm layer of finishing plaster (skim) is applied on top. This two-stage process gives the strongest, most crack-resistant result.
Plaster Coverage Rates
| Plaster Type | Thickness | Coverage (m²/25kg bag) | Approx. Price (2026) |
|---|---|---|---|
| Multi-Finish (Skim) | 2mm | 7.5–9 m² | £10–£14 |
| Bonding Coat | 8mm | 2.4–2.8 m² | £9–£12 |
| Browning | 8mm | 2.3–2.6 m² | £9–£12 |
| Hardwall | 8mm | 2.3–2.6 m² | £10–£13 |
| One Coat | 10–13mm | 3–4 m² | £10–£13 |
Bonding vs Skim — What Is the Difference?
Bonding plaster (also called bonding coat or Thistle Bond-it) is an undercoat plaster. It is applied directly to the wall surface at around 8–11mm thickness. Its job is to build up the wall surface, fill out irregularities, and provide a strong, flat base for the finishing coat. Bonding plaster has excellent adhesion, especially on smooth surfaces like concrete blocks or painted walls where other plasters might not stick well.
Skim plaster (Thistle Multi-Finish is the most popular brand) is a finishing plaster applied at just 2mm thickness. It goes over the top of the bonding coat (or directly onto plasterboard) to create the smooth, hard surface that you paint. Applying skim is a skilled job — it must be trowelled flat and polished while it is setting to achieve a professional finish.
When to Use Each Type
- Bonding + Skim — Use on blockwork, brick, concrete, or when re-plastering walls after removing old plaster. This is the most common combination for solid walls.
- Browning + Skim — Similar to bonding but designed for more absorbent surfaces like brick. Browning plaster has added grit for a better mechanical key.
- Hardwall + Skim — High-impact undercoat for areas that need extra durability. Dries harder than standard bonding.
- Skim only — Use on plasterboard, or when the existing undercoat is still in good condition and just needs a fresh finishing coat.
- One Coat — Combines undercoat and finish in a single product. Applied at 10–13mm. Popular with DIYers because it eliminates the two-stage process, though professionals generally prefer the traditional bonding + skim for the best finish.
Drying Times for Plaster
One of the most common mistakes in plastering — whether done by DIYers or impatient professionals — is painting or wallpapering before the plaster has fully dried. Here are the typical drying times:
- Skim coat (2mm): 2–3 days in well-ventilated conditions
- Bonding coat (8mm): 3–5 days
- One coat (10–13mm): 4–7 days
- Full re-plaster (bonding + skim): 5–7 days minimum
DIY Plastering vs Hiring a Professional
Plastering is one of the most skill-intensive trades in construction. While many DIY tasks can be learned from YouTube videos and practice, skim plastering requires significant technique that takes years to master. Here is a honest comparison:
DIY Plastering
- Pros: Saves £150–£500 per room in labour costs; satisfying when done well; bonding coat is easier to learn than skim.
- Cons: Skim finish is extremely difficult to get right first time; mistakes are very visible; requires specialist tools (hawk, trowel, bucket trowel, mixing drill); plaster sets fast, leaving little time for corrections.
- Best for: Patching small areas, bonding coats, garage or utility rooms where a perfect finish is less critical.
Professional Plasterer
- Pros: Smooth, perfect finish; fast (a professional can skim a room in 3–4 hours); guaranteed quality.
- Cons: Cost of £150–£500+ per room; availability (good plasterers are often booked weeks ahead).
- Best for: Living rooms, bedrooms, hallways — anywhere the finish quality matters.
Tips for Buying Plaster
- Check the date: Plaster has a shelf life of around 3 months from manufacture. Old plaster sets too quickly and gives a poor finish. Always check the use-by date on the bag.
- Store properly: Keep bags off damp floors (use a pallet or board) in a dry, indoor location. Moisture ruins plaster.
- Buy from builders' merchants: Prices at Wickes, Travis Perkins, or Selco are typically 20–30% lower than general DIY stores like B&Q or Homebase.
- Buy in bulk: Multi-bag deals often save £1–£2 per bag. If you need more than 5 bags, ask about pallet pricing.
Frequently Asked Questions
A 25kg bag of finishing plaster (skim) covers approximately 7.5–9 square metres at 2mm thickness. For bonding coat at 8mm, a 25kg bag covers about 2.5 square metres. Use the calculator above for an exact figure based on your wall area.
Bonding is an undercoat plaster applied at 8mm thickness to build up and flatten the wall. Skim (finishing plaster) is applied on top at 2mm to create the smooth, paintable surface. Most jobs require both layers.
Skim coat dries in 2–3 days, bonding coat in 3–5 days, and a full re-plaster in 5–7 days. Wait until the plaster turns uniformly light-coloured before painting. Do not use heaters to speed drying as this causes cracking.
Professional plastering costs £150–£500 per room in 2026 for labour. Materials cost approximately £10–£14 per 25kg bag. A typical room requires 2–4 bags of bonding and 2–3 bags of skim, so materials run about £40–£80 total.