DIY earth bricks

pressed-earth-bricks

Creating pressed earth bricks isn’t hard when you have a machine and willing helpers. John Hermans describes the process and advantages of this low embodied energy approach to construction.

THIS article aims to inspire owner-builders to minimise the carbon footprint of their new sustainable dwellings by using pressed earth bricks. By explaining the many virtues of this building material, I hope to spark interest in my offer to share the amazing machine that I use to make them.

I started making and using pressed earth bricks in 1988, shortly after commencing excavation for our house site. I had seen a hydraulic brick press working very effectively around this time and, with the intent of making a copy, I took several photographs of it in operation. I then found four aspiring owner-builder friends who were willing to become ‘shareholders’ and finance the brick press fabrication; my input was to build it.

The machine I built back then is still going strong today. To date, this press has made in excess of 70,000 bricks and has been responsible for some very creative, cost-efficient and low embodied energy housing.

A pressed earth brick is simply a brick made by compacting soil that has a high percentage of clay. The machine compacts the soil by 50% using the power of a hydraulic press. The result is an attractive and easy-to-use brick that needs no firing and can often be made from subsoil excavated from the house site— and thus has much lower embodied energy than the average house brick.

My machine makes bricks that are 300 mm long by 220 mm wide by approximately 130 mm high, so quite a bit larger than the average house brick (dimensions 230 x 110 x 76 mm). The height of the brick depends on the amount of clay mix put into the press, but averages around 130 mm. At that size, the brick ends up weighing around 15 kg.

It is important to seal the bricks to prevent surface erosion. There are many earth brick sealing products available now (e.g. Your Home suggests linseed oil and turpentine; or you can use one of the Bondall products).

Quality bricks are achieved by using a clay-based subsoil that will bind well and dry hard. This is often an excavation waste product, with little commercial value. Using a press to make several test bricks is a sensible idea.

An addition of 5% to 10% cement will form a brick that will handle days of total water submergence, although this is a condition rarely encountered! No cement is needed in the mix if the bricks are used indoors. If used in exterior walls that are likely to be impacted by rain, then the use of cement is recommended.

Read the full details in ReNew 138.