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Cavity Walls & Interior Linings

Cavity Walls, External Veneer and Interior Wall Linings

There was a time when the external walls of buildings were generally built of stone, they were often very thick with rough surfaces. Modern building have walls that are often very light, have internal cavities and very smooth interior finishes. How did the design of walls evolve, what are the advantages of cavity walls and modern wall construction methods?

Here we look at wall construction, the design of cavities, external veneers and internal linings.

The Evolution of The Walls Of Buildings

An insulated cavity wall

There was a time when the walls of buildings were built from stone, wood, bamboo or grasses. Stone wasll tended to be thick and rough and were very labour intensive to find, cut and transport while wood and grasses deteriorated with time.

The development of baked clay "red" bricks in the middle east revoltionised building and became the wall building material of choice across the world. In recent years concrete blocks have replaced brick for many applications.

The Purpose of A Building's Walls

Walls, of course, carry out two basic functions:

  1. They support the roof
  2. They close off the space inside to protect it from the weather and to contain or keep out heat.

In different countries these two purposes have been dealt with in different ways.

In Britain walls tend to be structural, they support the roof and this is achieved by using structral strength hard bricks or concrete blocks which tend to be built in a double thickness of brick.

In America and Australia houses are buitlt with a structural wooden frame that supports the roof. This frame is then lined on the inside with "plasterboard" (known as "drywall" in America and "Gyprock" in Australia) and covered on the outside with a "veneer" of "siding" (wooden or cementboard planks) or bricks. Bricks used for wall veneers tend to be lightweight and not strong, there purpose is for appearance and to resist weather. Roofs in America are usually made from lightweight bitumen shingles while in Australia heavy cement tiles are usually used.

In other parts of the world, particularly where earthquakes are common, buildings often have a strong structure of reinforced concrete columns and beams, this structure supports floors and roofs. Lightweight concrete blocks or bricks are used to fill in the walls between the concrete columns. Thse blocks are usually finished on both sides with a thin layer of cement.

Cavity Walls

In many parts of the world, especially cold climates, it was found that walls easily transfer heat. In the depths of winter even the thickest of walls were not able to retain the heat from an internal fire, in fact the walls soaked up the heat.

With the advent of brick for wall building it was soon found that by building a wall with a cavity the wall provided very effective insulation which considerably improved the building's ability to retain heat in winter and keep out the heat in summer.

So what is a cavity Wall?

A cavity wall is a double layered wall with an air gap between. In the case of a brick wall the wall has two separate single brick walls with a gap about the width of a brick between them. The brick easily tranfers heat, and sound and water but the air gap does not. Heat and sound is not easily transferred therough the wall and if teh outside layer gets wet it does not soak through to the inner wall.

Modern walls often have cavities and in many parts of the world they are a legal requirement.

In Britain walls are generally a double layer of brick with an air gap between the layers. It should be noted that In the double layered brick cavity walls in Britain, galvanised steel "ties" are embedded between the bricks to link the inner and outer layers of brick together to improve the structural strength of the walls.

In Australia and America the air gap is in the wooden structure with the internal layer being the plasterboard finishing and the outer layer being the brick or siding veneer. Often these days the cavity has insulation material such as glass wool or aluminium foil and waterproof membranes in it to improve the insualtion properties.

The advantages of cavity walls are:

  1. Heat insulation
  2. Sound insulation
  3. Prevention of water penetration.

Cavity Walls in Tropical Climates

It is unfortunate that, in tropical climates where air conditioning is widely used, cavity walls are virtually never used probably owing to the increased building cost. The high cost of air conditioning may eventually lead to the introduction of cavity walls in Tropical climates.

There are many new materials on the market thse days and an effective insulation can be provided to solid concrete walls (and ceilings) by fixing a double layer aluminium sandwich insulation on the inner surfaces of walls with a layer of plaster board on top of that. The aluminium insulation sandwich has two layers of strong aluminium foil with bubble wrap or sponge between the layers to provide an air gap.

Horsehair Wall Linings

In old Victorian houses the walls were lined in a rather peculiar way. Stone walls were rough and it became the fashion that the walls and ceilings were lined with wooden lathes and plaster mixed with horse hair. To this day many old buildings across Europe have walls and ceilings built in this way.

Stone walls were very rough and to make them smooth plaster could be put directly onto the wall. Unfortunately dampness came through the walls.

Then someone found that by building two walls with a narrow air gap between them houses became drier and warmer. The "cavity" provided insulation and stopped the dampness from getting from the outer wall to the inner wall. Standard practice in many parts of the world is to build houses with cavity walls.

Plasterboard, Drywall and Gyprock Wall Linings

Builders are constantly seeking ways of reducing house building costs and there have been many developments. By far the most sweeping change has been the development of "plasterboard" which is also known as gypsum board, drywall (America) and Gyprock (Australia).

Plasterboard is a 12mm thick sandwich of gypsum plaster between two pieces of cardboard. Wood fibre is mixed with the plaster to increase its strength (they ran out of horse hair a long time ago). Sheets are usually 1.2 metres by 2.4 metres. These are nailed onto a wooden or light steel frame and then finished by plastering over the joints and nail holes. The nails used are large diameter flathead nails that are galvanised so they won't rust

Plasterboard is quick and easy and gives a very smooth flat surface. In days past plastering was a real artform. A team of men would be able to plaster a room, 4 walls and a ceiling, in a couple of hours literally throwing the plaster at the walls and with great skill skimming it very smooth and flat. Plasterboard is changing all that and plastering is now a dying trade.

Plasterboard is now being used widely in tropical climates particularly for ceilings. The locals know it simply as gypsum. It is a very useful material but has two weaknesses.

  1. Firstly it breaks easily so when someone falls against the wall and can easily put an elbow through it.
  2. Secondly it does not like water and has a tendency to fall apart if it gets wet. Check your walls and particularly ceilings. If you see any signs of water drips on plasterboard ceilings from leaks in your roof, get the roof leaks fixed quickly or you will end up wearing your ceiling. Also note that dampness will often leave mildew patches on plasterboard.

Most walls in many parts of the world are still built the traditional local way. Walls are built without a cavity using light concrete blocks known as "batako". These are then "rendered" with a thin layer of concrete. The surface is finished off with a final skim of high density cement. The original Dutch method produced a high quality very stable finish. Sadly their skill has been lost and many external walls these days end up with a hard skin of cement that cracks and falls away from the concrete beneath.

You will probably find your walls are finished in this way. The high density cement is very hard as anyone who has tried to hammer picture hooks into their walls will have found.

In outside areas you may find the surface of the walls (and also flat concrete roofs) are "crazed" with a network of fine cracks through the thin concrete skim. This is due to the differential expansion and contraction between the skim and the concrete beneath and are the first signs that the cement is delaminating. Expect the cement skim to start chipping away or falling off.

We have come a long way since the days of horsehair and lathes. Building walls is a lot easier and cheaper than it used to be.

Copyright © Phil Wilson December 2008
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