Render vs Plaster — External & Internal Finishes
Understanding the difference between external render and internal plaster — materials, application, drying times, costs and when you need each.
Side-by-Side Comparison
| Property | Internal Plaster | External Render |
|---|---|---|
| Purpose | Smooth finish on internal walls/ceilings | Weather protection & finish on external walls |
| Base material | Gypsum (calcium sulphate) | Cement, lime, or proprietary polymer |
| Common products | Thistle Multi-Finish, Hardwall, Bonding | Sand & cement, K Rend, Weber, Parex |
| Typical thickness | 2-3mm (skim), 11-13mm (undercoat) | 15-20mm (two coats), 12-15mm (monocouche) |
| Number of coats | 1-2 coats | 2-3 coats (or 1 monocouche) |
| Setting time | 1-2 hours | 24 hrs between coats |
| Full drying time | 2-5 days | 7-28 days |
| Weather resistance | None — indoor use only | Designed for full weather exposure |
| Cost per m² (installed) | £15-25 | £40-80 |
| Typical lifespan | 30-50+ years | 20-40 years |
Pros and Cons
Internal Plaster
Pros
- + Quick setting time — same-day finishing
- + Smooth, paint-ready surface
- + Lower cost per m²
- + Easy to repair patches and cracks
- + No scaffolding needed
Cons
- - Cannot be used externally
- - Damaged by water and damp
- - Requires a sound, stable background
- - Short working time once mixed
- - Skill-dependent finish quality
External Render
Pros
- + Weatherproofs and protects external walls
- + Wide range of finishes and colours
- + Improves thermal performance
- + Transforms property appearance
- + Monocouche gives through-colour finish
Cons
- - More expensive than internal plaster
- - Scaffolding usually required
- - Weather-dependent application
- - Longer curing times (days to weeks)
- - Sand/cement render can crack over time
UK Cost Comparison (2026 Prices)
| Finish Type | Materials per m² | Labour per m² | Total per m² |
|---|---|---|---|
| Skim plaster (internal) | £2-4 | £12-20 | £15-25 |
| Undercoat + skim (internal) | £4-7 | £18-28 | £22-35 |
| Sand & cement render (external) | £5-10 | £30-50 | £40-60 |
| Monocouche render (external) | £12-18 | £35-55 | £50-75 |
| Silicone render system (external) | £15-22 | £40-60 | £55-80 |
Note: external render prices include scaffolding. Internal plaster prices assume plasterboard or sound masonry background.
When to Choose Each
You Need Plaster When
- Finishing internal walls or ceilings
- Creating a smooth surface for painting
- Skim coating over plasterboard
- Patching damage inside the property
You Need Render When
- Weatherproofing external walls
- Changing the appearance of brickwork
- Part of an external wall insulation system
- Covering damaged or mismatched external masonry
Related Calculators
- Rendering Calculator — calculate sand and cement for external render
- Plaster Coverage Calculator — bags of plaster for internal walls
How We Calculate This
Frequently Asked Questions
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Last updated: April 2026
All calculations are estimates. Verify with your supplier.