Types of lightweight concrete
One way to get lightweight concrete is to aerate the concrete before casting and this is the method adopted to produce the white lightweight blocks filled with small air bubbles called Hebel used by many sculptors for its easy carvability and the fact that it is readily available at most hardware stores.
For the Do-it-Yourselfer replacing the air bubbles with lightweight materials is an easy and effective alternative requiring no expensive plant to produce.
Materials used to make lightweight concrete
The materials usually used are vermiculite, peat moss, perlite, granulated polystyrene foam, or lightweight scoria sand, all having a greater o lesser effect on reducing the weight of the heavy weight aggregates normally used in building construction concrete. To reduce the loss of some strength, normally chicken wire or fibremesh is used in the construction process.
Typical Lightweight Concrete Products
Garden ornaments, pots, planters, seats and flower containers immediately come to mind. Many are large and have to moved quite often during their lifetime.
Reproduction stone is increasing in popularity, as the ecological benefits of not denuding the outdoors of natural stone become more obvious.
What is Hypertufa?
Tufa is a spongy cellular rock found in limestone country. “Hypertufa” is a man made substitute. The spongy nature of Tufa came about by the leaching out by water of much of the materials of the original rock leaving the spongy amorphous material known as Tufa.
In Ireland and England in particular this material has for centuries been used to make animal watering troughs due to the ease with it could be carved to shape.
It did not take long for gardiners to realise its adaptability and attractiveness and begin carving and shaping Tufa to make beautiful natural, antique looking pots, planters and stepping stones for their backyards.
Worldwide, with the diminishing availability of Tufa, people have had to start looking for alternatives. A mixture of cement, sand and peat moss called Hypertufa was the answer, an easy to make attractive lightweight concrete, similar to the limestone and vegetable matter origins of Tufa.
This original formula has been improved and expanded as a greater range of lightweight materials became available.
Suggested Hypertufa or Lightweight Concrete Formulas.
There are countless formulas available for you to experiment with to find your perfect solution, based on cost, local material availability strength and appearance. The following 2 basic formulas can be altered to provide all the choice you require.
Formula #1 is more expensive but provides a granite like appearance when using grey Portland cement that is most attractive.
You reduce cost and increase strength by using sand in the mix, see Formula #2. Reduce cost further by using sand and cement rather than ready mix.
1 part Portland Cement
1 part vermiculite or perlite (small to medium grade)
1 part peat moss
1 part Ready Mix Sand and Cement
1 part peat moss
1 part perlite or vermiculite
The ingredients of your formula
A plastic bucket
Moulds or mould substitutes
Chicken wire (galvanised) or fibre mesh
Vegetable oil spray
Tools including wire cutters, rasps etc
Wheel barrow or large plastic tub.
Mixing Your Dry Ingredients
The critical ingredient is the water. How moist or how dry you want to make your mix, depends on the type of project, so as with many things practice makes perfect.
The first thing to remember, is that the Portland Cement mentioned in the formulas is not concrete, it is one of the ingredients of concrete. It is available in white or grey. Unless you are looking for a special effect only possible by using white cement, grey will suffice for the majority of your projects.
Use the same size container for all ingredients, to keep to the proper ratio of ingredients for each formula.
Place the dry ingredients into the plastic tub, wheelbarrow or cement mixer you are using and add water gradually till the mix can be formed easily with your hand. Not too dry and not too moist.
If using colour in the mix add it before commencing to mix, particularly if it is a liquid colour as the addition of extra water when the mix has finished, could make it too moist.
Casting Your Mould
Your mould could be as simple as a large and a small cardboard box. One for the outside and one for the inside, if you are after a simple rough and ready project.
Small and medium sized commercially produced garden planters, are still usually made with a latex outside mould, supported in the correct shape by fibreglass .Another latex mould is used to provide the correct shape to the interior of the mould. The method for making these moulds will be covered in a later article.
A suitable mould for a one off DIY project could be a plastic container of the right shape for the outside mould and a cardboard box for the inside. When the concrete had set, simply collapse the box and then remove the casting from the mould. Ensure easy release from the mould by spraying the mould with vegetable oil to act as a release agent.
New Product for Commercial Producers:
A light weight product that is being used by an increasing number of manufacturers of planters and other light weight garden products is Aerolite Scoria sand, quarried in Victoria by Aerolite Quarries Pty Ltd www.aerolite.com.au Unlike some other scoria products Aerolite’s products are half the weight of equivalent aggregate. Well worth contacting for information.