Basic Mud Bricks are made be mixing earth with water, placing the mixture into moulds and drying the bricks in the open air. Straw or other fibres that are strong in tension are often added to the bricks to help reduce cracking.
Virtually all the energy input for mud brick construction is human labour (indirectly, fueled by the sun) and after a lifetime of use, the bricks break back down into the earth they cam from.
The appearance of mud bricks reflects the materials they are made from. They are thus earthy, with colour determined y colour of clays and sands in the mix.
With thick enough walls, mud brick can create load bearing structures up to several stories high. Vaults and domes enable adobe to be used for many situations other than vertical walls.
Adobe walls can provide moderate to high thermal mass, but for most Australian climatic conditions, as a rule of thumb, walls should be a minimum of 300mm thick to provide effective thermal mass.
Contrary to popular belief mud bricks are not good insulators. Since they are extremely dense they lack the ability to trap air within their structure, the attribute of bulk insulation that allows it to resist the transfer of heat. But Queensland doesn’t need really high insulation, as it is a relatively temperate climate.
A well-built adobe wall has very good sound insulation properties. In fact, it can be almost equivalent to a monolithic masonry structure in its capacity for sound attenuation.
Since earth does not burn, and earth walls do not readily provide habitat for vermin, mud brick walls generally have excellent fire and vermin resistance.
Adobe walls are capable of providing structural support for centuries but they need protection from extreme weather (with deep eaves).
Ideally earth should be used in its natural state or as ear as it can be achieved. Don’t use one’s with bitumen as they release hydro carbons.
Adobe should not contain any organic matter – the brick should be made from clays and sands and not include living soil. They require very little generated energy to manufacture, but large amounts of water.
The greenhouse gas emissions associated with unfired mud bricks can be very low.
Low costs in construction can only be effectively achieved by self build, reducing the labor costs associated by self build, reducing the labor costs associated with manufacture and laying of bricks.
Typical Domestic Construction:
The potential for sourcing the main wall construction material from one’s own site, making the bricks, and building the walls, can be very appealing as both an economic and lifestyle choice.
Before excavating for on site mud, consider the site layout to minimise carrying and transport and ensure there is space to keep any topsoil separate for use on the garden.
A typical standard mud brick is between 300 – 375mm long, 250 -300mm wide and 125mm high and can weigh up to 18kg.
Although Adobe can be load bearing, there is also widespread use of frames. The advantages of this ar that a roof structure can be erected to provide weather protection or both mud brick making and construction.
All masonry walls ar required to have movement/expansion joints at specified intervals.
A raft concrete slab can provide a clean, flat surface for making mud bricks.
A damp proof course must be laid between the footings and brick wall to prevent rising damp.
A splash course of fired bricks is advisable to prevent erosion of the lower course of mud bricks resulting from heavy rain.
Fixings & Finishes:
Strong fixing can be achieved by embedding dowels or plugs into a wall.
After brushing to get a fairly even surface, the final finish is a mud slurry, typically finished by hand.
Linseed oil and turpentine can be used to provide a final finish to prevent erosion.