Plastering and Rendering: What's the Difference?

When planning renovations, you'll frequently encounter terms "plastering" and "rendering." While related, they're different processes used in different locations with different materials. Understanding these differences helps you communicate effectively with builders, make informed decisions, and appreciate the work involved in your renovation. This comprehensive guide explains plastering and rendering, their types, applications, and when each is appropriate for your London property.

The Basic Difference

The fundamental distinction is simple: plastering is applied to internal walls and ceilings, whilst rendering is applied to external walls. Both involve coating surfaces with mixtures that set hard, creating smooth or textured finishes. However, they use different materials suited to their specific environments—internal plaster needn't withstand weather, whilst external render must resist rain, frost, and temperature changes.

Understanding Plastering

What is Plastering?

Plastering involves applying plaster to internal surfaces—walls, ceilings, and occasionally floors in heritage properties. It creates smooth, durable surfaces ready for decoration. Plastering serves multiple purposes: providing smooth surfaces for painting or wallpapering, hiding imperfections in underlying surfaces, providing some thermal and acoustic insulation, and protecting underlying structures.

Types of Plaster

Gypsum plaster: Modern gypsum-based plasters are standard in contemporary construction. Brands like British Gypsum's Thistle range are ubiquitous. Gypsum plaster is applied in two coats: a backing coat (browning or bonding) provides bulk, followed by a finishing coat (multi-finish or board finish) creating a smooth surface. Gypsum plaster sets relatively quickly (2-3 hours), is easy to work with, and provides excellent smooth finishes.

Lime plaster: Traditional lime plaster, used for centuries, is still appropriate for period properties. Made from lime, sand, and sometimes hair or fibres, lime plaster is breathable, allowing moisture to evaporate through walls. This is crucial for solid-walled period buildings designed to breathe. Lime plaster remains slightly flexible, accommodating building movement without cracking as readily as harder modern plasters. It sets slowly (weeks to fully cure) and requires skilled application, but it's essential for authentic period property renovation.

Clay plaster: Increasingly popular in eco-builds, clay plaster offers natural, breathable finishes with excellent humidity regulation. Whilst less common in mainstream renovations, it's worth considering for environmentally conscious projects.

Plasterboard and Dry Lining

Modern construction often uses plasterboard (also called plasterboard or gypsum board) rather than wet plastering. Large boards are fixed to walls or ceilings, then joints are filled and a thin skim coat applied. This is faster and cheaper than full plastering, though some argue it lacks the solidity of traditional wet plaster on block or brick.

Plastering Techniques

Several plastering approaches exist depending on substrate and requirements:

Skimming: Applying a thin finishing coat over plasterboard or existing plaster to create fresh smooth surfaces. Common in renovations where walls are sound but surfaces are dated or damaged.

Two-coat plastering: Applying backing coat followed by finishing coat directly to brick, block, or stone. Used in new builds or when walls are stripped to original surfaces.

Three-coat plastering: Traditional method using base coat, floating coat, and finishing coat. Now rare except in high-quality heritage work.

Understanding Rendering

What is Rendering?

Rendering applies protective and decorative coatings to external walls. Like plaster, render can be smooth or textured and comes in various types suited to different situations. Render protects underlying walls from weather, provides additional insulation, and enhances appearance while allowing vapour permeability in breathable versions.

Types of Render

Cement render: Traditional cement-sand render (typically 1:5 or 1:6 cement to sand) is durable and weather-resistant. It's applied in two or three coats and can be painted once cured. However, cement render is relatively impermeable, which can cause problems on old buildings by trapping moisture. It's prone to cracking if incorrectly specified or applied. Use cement render on modern buildings with damp-proof courses and cavity walls, but avoid it on solid-walled period properties.

Lime render: Like lime plaster, lime render is breathable and flexible. It's essential for period properties with solid walls. Lime render allows moisture absorbed by walls to evaporate outward, preventing the damp problems that cement render can cause on old buildings. It requires skilled application and takes weeks to cure fully, but it's the appropriate choice for buildings constructed with lime mortar—essentially anything built before the early 20th century.

Monocouche render: Modern one-coat render systems are increasingly popular. Applied in a single thick coat, monocouche renders are quicker to apply than traditional renders. They come in various colours and textures, eliminating the need for painting. Many are polymer-modified for improved flexibility and water resistance. However, quality varies between products, and repairs can be tricky if colours don't match exactly.

Acrylic render: Flexible, polymer-based renders that are very water-resistant and come in numerous colours. They're applied thinly over insulation boards in external wall insulation systems. Acrylic renders resist cracking well but aren't breathable, so they're unsuitable for period buildings without specialist advice.

Silicone render: Premium render offering excellent water repellency while maintaining some breathability. Self-cleaning properties reduce algae growth. More expensive than other renders but offers very long life with minimal maintenance.

Render Finishes

Render can be finished in various ways affecting appearance and texture:

Smooth finish: Troweled smooth for contemporary aesthetics. Can be painted once cured.

Scraped finish: Slightly textured by running scrapers over partially set render, revealing aggregate.

Tyrolean or splatter dash: Render applied by throwing or spraying, creating rough, textured finishes. Common on 1960s-80s properties but somewhat dated now.

Pebbledash: Small stones thrown onto wet render, creating very textured finishes. Traditional in some areas but unpopular with many buyers. Difficult to maintain or alter.

When to Use Each

Plastering Situations

You'll need plastering when: renovating interiors and wanting fresh wall surfaces, converting lofts or basements into living spaces, creating new internal walls (stud walls with plasterboard), repairing damaged existing plaster, or restoring period properties (use lime plaster).

Rendering Situations

Rendering is needed when: existing render is damaged or failing, extending properties and needing to finish new external walls, wanting to change your property's external appearance, improving thermal performance with external wall insulation systems, or protecting exposed brickwork in harsh weather locations.

Costs

Costs vary based on property size, surface condition, and material choices.

Plastering Costs

Expect to pay: £15-£25 per square metre for skimming over plasterboard, £25-£40 per square metre for two-coat plastering on walls, £30-£50 per square metre for ceilings (harder to work on), and £40-£70+ per square metre for lime plastering (requires specialist skills).

Whole room costs depend on size but might be: £300-£500 for small bedrooms, £500-£800 for living rooms, £600-£1,000 for large open-plan areas.

Rendering Costs

External rendering costs: £40-£60 per square metre for cement render, £50-£80 per square metre for lime render, £60-£90 per square metre for monocouche render, and £70-£100+ per square metre for premium silicone renders or complex situations.

Whole house rendering for typical terraced houses: £4,000-£8,000 depending on house size, render type, and access difficulties.

Period Property Considerations

Victorian and Edwardian properties require specific approaches. These buildings have solid walls (no cavities) built with lime mortar and bricks that absorb moisture. They're designed to breathe—moisture absorbed from rain or internal sources evaporates through wall materials. Trapping moisture with impermeable modern materials causes damp, decay, and structural damage.

For period properties, always use: lime plaster internally, lime render externally (if rendering at all—many period properties have exposed brick), and breathable paints.

Never use cement render on solid-walled period properties—it traps moisture causing extensive damage. Similarly, gypsum plaster can cause issues if used extensively in very old buildings, though it's acceptable in limited applications.

Modern Properties

Post-1930s properties typically have cavity walls and damp-proof courses. Modern materials work well: gypsum plaster internally is standard and performs excellently, cement render externally is appropriate and durable, and modern paints are fine.

However, even modern properties benefit from breathable materials in some situations, particularly in poorly ventilated areas prone to condensation.

The Application Process

Plastering Process

Professional plastering involves: preparing surfaces (cleaning, ensuring they're sound, applying PVA bonding where appropriate), applying backing coat and levelling (if required), allowing backing coat to partially set, applying finishing coat in thin layers, trowelling to smooth finish, and allowing proper drying time before decoration (typically 2-4 weeks depending on conditions).

Rushing decoration before plaster is fully dry causes problems—paint peels, and trapped moisture can cause damp issues.

Rendering Process

External rendering involves: preparing walls (cleaning, repairing defects, ensuring good key for render), applying scratch coat and keying its surface, allowing scratch coat to set, applying top coat(s), achieving desired finish, and curing properly (keeping render damp in hot weather, protecting from frost in cold weather).

Rendering requires favourable weather—not in freezing conditions, very hot direct sun, or heavy rain. Timing projects appropriately is crucial.

Common Problems and Solutions

Plaster Cracking

Cracks occur due to structural movement, inadequate drying time between coats, applying finish coat too thickly, or inappropriate materials for substrate. Small cracks can be filled, but extensive cracking often indicates underlying issues requiring investigation.

Render Failure

Render fails due to incorrect mix ratios, poor adhesion to substrate, trapped moisture (particularly with cement render on old buildings), frost damage during curing, or building movement. Failed render must be removed and replaced—repairs rarely match well. Addressing underlying causes is essential before re-rendering.

Blown Plaster or Render

"Blown" plaster or render has separated from the underlying wall. It sounds hollow when tapped and eventually cracks and falls off. Causes include moisture damage, poor key, or inappropriate materials. Blown areas must be cut out and replaced—they won't reattach.

DIY vs Professional Work

Both plastering and rendering are skilled trades requiring practice to achieve quality results. Poor plastering or rendering is obvious and devalues properties. Unless you have experience, employ professionals. Costs are reasonable relative to the importance of good results and the difficulty of correcting poor work.

For very small repairs, DIY is reasonable using patching plasters available from DIY stores. But for whole rooms, new render, or period property work, use skilled plasterers.

Maintenance

Internal plaster requires minimal maintenance—just redecoration as desired. If cracks appear, investigate causes before filling. External render needs more attention: inspect annually for cracks or damage, repair small defects promptly before they worsen, repaint rendered surfaces every 7-15 years depending on exposure and paint quality, and keep render clean—pressure washing carefully when needed.