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A Definitive Guide to Plaster and Render

Plaster and Render

Plastering was a standard means of finishing interior walls and partitions, from the Renaissance to the 20th century.

Plastering is a process of covering rough surfaces with a plastic material to obtain an even, smooth, regular, clean and durable surface. External plastering is termed as rendering which improves the resistance of the surface to rainwater penetration and other atmospheric influences. Plasters for indoor use have to be abrasion resistant and suitable for decorating with any coating/tiles/wallpaper

Thickness can vary from 1 – 20mm depending on location and function. Usually, two or more coats are applied.

Plaster is made by heating gypsum above 302 degrees Fahrenheit (150 degrees Celsius), which causes
the embedded water in the gypsum to evaporate. Dry plaster powder is used to create a workable paste
by adding water. The resulting paste will harden into a solid.

Material Properties

  • Gypsum Plaster has good fire resistance, it is breathable, has good capillary force, moisture-controlling characteristics, low-thermal insulation, warm surface, is heat retaining, sound-damping, elastic, controlled setting, and is fire-retardant.

Types of Plaster and Render

1.Cement Render/Plaster

  • Traditional form of render.
  • Created by mixing cement, sand, water in suitable ratio /proportions.
  • Used internally and externally mostly where water resistance surface is required.
  • Usually applied on rough surfaces like brick, stone, concrete surfaces.
  • Available in a variety of colors – natural or pigmented.

Finish :

Ranges from smooth to textured.

Pros :

  • Economical and effective.
  • Stronger and harder than lime render.
  • Easy to apply
  • Fireproof

Cons:

  • Extremely rigid and brittle – could crack or break easily.
  • Not waterproof and have to be finished by applying paint.
  • Recycling is hard/difficult.

2.Lime Render

  • Traditional form of render.
  • Prepared by mixing sand and lime in equal proportions, cement sometimes added to improve strength.
  • Flexible thereby reducing the risk of cracking.
  • Leaves a traditional attractive finish

Pros :

  • Less rigid and brittle than cement render.
  • Durable
  • Eco-friendly and recyclable
  • Useful in ‘breathing wall’. It can store water and dry out easily

Cons:

  • Requires expensive and skilled labor.
  • More difficult to work than cement render
  • Takes more time to cure than cement render

3.Mud Plaster

  • Oldest and cheapest form of plaster.
  • Commonly seen in rural areas and in structures of temporary character or low-cost housing.
  • Made from earth mixed with chopping straw, hay or hemp with water in proportionate ratio.

Pros:

  • Environment-friendly
  • Cost-effective
  • Easily repaired

Cons:

  • Do not provide resistant to rain.
  • Poor resistance to erosion

4.Stucco

  • Stucco plaster acts as a decorative feature and gives an excellent finish.
  • Used for interior as well as exterior surfaces.
  • Usually laid in three coats with thickness of 25mm.
  • The first coat is called scratch coat, second a finer coat, also known as brown coat, and third is called the white coat or finishing coat.
  • Made up of aggregates, binder, and water.

5.Acoustic Plaster

  • Relatively low density plaster.
  • Contains Vermiculite and used to increase sound absorption.

6.Gypsum Plaster and Render

  • Calcium hydroxide combined with sand, water, and additives to control the setting.
  • Applied in three coats.(Scratch, Brown, and Finish)

7.Molding Plaster

  • Made from extremely finely ground gypsum and hydrated lime.
  • Used for ornamentation because their fine grain preserves precise detail.

8.Veneer Plaster

  • Ready-mixed plaster
  • Used as one-or two coat plaster finish over a substrate.

Modern Renders

Polymer Render

  • Alternative to traditional cement render.
  • Added polymers to cement prevent cracking and help cement adhere better.
  • Mostly suited for external surfaces and is weather-resistant.
  • Applied on modern brick walls, lightweight cement blocks, insulation boards.

Pros:

  • Weather-resistant
  • Flexible and strong than cement binder
  • Less prone to cracking

Cons:

  • Limited to a few background depending on polymer
  • Not ecofriendly.

Acrylic Render

  • Acrylic resin is added in mix during manufacture.
  • Used as finished coat for previous renders.
  • To get desired finish, aggregates are added.

Pros:

  • More flexible and less prone to cracking
  • Moisture resistant

Cons:

  • Not breathable
  • Not eco-friendly option.

Monocouch Render

  • Monocouch means a single layer.
  • Provides protection from weather and acts as a decorative feature

Pros:

  • Weather-resistant and breathable
  • Does not need painting

Cons:

  • Expensive
  • Not crack resistant.

Other Types

  • Silicon Render
  • Waterproof Plaster
  • Composite Plaster
  • Lath and Plaster on Timber
    • Lathing may be either of wood or of expanded metal. Wooden lath is used for forming a ground for plastering timber partition walls and ceilings of timber floors. Laths are thin strips of well-seasoned wood fixed by nails in parallel to wooden frames.10mmm gap is provided between two successive strips for plaster. The plastering is then done in a usual manner.

Types of Finish

Smooth Cast

The finish is leveled and smooth surface.

Mortar is made by mixing cement and fine sand in ratio of 1:3

Rough Cast

Final coat/finish in which mortar contains big size aggregates which vary from 3-12mm.

Waterproof, durable and resistant to cracking.

Pebble Dash

Finish in which mortar which contains small pebbles or crushed stones.

Waterproof, durable and resistant to cracking.

Scrapped Finish

The final after being leveled is scraped with a straight edge, old saw blade or other tool.

Various types of scrapped finishes are obtained by using different tools.

Textured Finish

In this finish, ornamental patterns or textured surfaces are produced by working with various tools.

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