Testing for soils needs to include; compressive strength, shrinkage, erosion/water penetration and a wet/dry appraisal test (wet/dry appraisal tests for such things as cracking, swelling, pitting, etc.).

Initial testing for wet/dry appraisal and erosion/water penetration indicate that this soil performs similar to the Raglan/Moerangi soil that we have had such great success with over the past 20 years. Shrinkage tests, also the same. Compression testing suggests that the Mangawhai soil is indeed stronger than soils we have commonly used in the past.

Compressive strength is typically measured as MPa (Megapascals). For rammed earth a target strength is commonly set at between 3 to 4 MPa. Our first results were tested at the Opus Laboratory in Albany and came in at over 10 MPa for the three test cylinders crushed.

Along with the apparent quality of the samples tested, it is also very encouraging that the soils are relatively common to access in the area and have an attractive smooth finish once rammed. I am also anticipating that this soil will be reasonably trouble free for mixing and ramming – making for happy rammers.

It is very easy to feel overwhelmed with this task and consequently a little threatened by it as well.

Over the last 20 years I have built as many as 80 dwelling structures, of these homes I have designed, project managed and built as many as 50 of them. In this time I have had the responsibility of guiding many first homeowners through their first experience of design development. In my experience I have found that the initial approach to design is crucial as it will make or break the projects feasibility.

Our design philosophy in Terra Firma is to initiate an approach to design that encompasses individual needs and wants, construction efficiency / buildability, structural integrity and possibly the most important (and often most compromising factor) – affordability.

I will focus here on affordability.

When I get approached with a request to start design development of a new home it’s very important to me to that you have as much involvement in the design process as they are comfortable with. Firstly so that things can get underway I will give you some homework. This homework comes in the form of three questions that you will need to research so as to make a sensible start to the concept plan;

-        How many rooms / spaces are required.

-        What each space / room is for.

-        The minimum size requirement for each room that you would comfortably be prepared to live with.

The first two tasks are relatively simple exercises, it is the third task that needs the most consideration and therefore research.

The reasoning behind the minimum size requirement is obviously cost driven (which is also a sustainability issue). Here at Terra Firma our aim is to facilitate an enjoyable project experience, if we can develop a plan that, with the most economical use of use of floor area, can fulfil your needs and most of your wants, then we will know emphatically the question of design feasibility. Also what this approach means as far as design development is, is that once we have gone through the initial exercise and then come up with a cohesive concept plan then we can do a first cost estimate. If this first cost estimate comes well within your proposed budget then we can look at incorporating more of your wants / special features etc into the design, or conversely have the pleasant reality of having money left over (yay). This design development theory hopefully will have the effect of creating a more enjoyable process – it is always a much more pleasant experience to be able to increase the size of a project rather than having to make cuts that you may have set your heart on.

Happy home designing.

As New Zealand’s leading Rammed Earth Construction Company, Terra Firma has built up years of experience in the techniques involved in working with rammed earth. Its clear how rammed earth can be used as a safe, low cost, non-toxic building material however we also recognize the function and finishing of a home as being a primary objective for our clients.

Whilst we build new homes’ walls using rammed earth, incorporating rammed earth floors is very costly in a new build. Rammed Earth Flooring as a technology had been used for hundreds of years however the research and development in modernizing the technology is still in its infancy.

Construction of Rammed Earth Floors takes a lot of time, is very labour intensive and has been seen to fall short of the high standard of quality Terra Firma assures its clients. Rammed Earth Floors also require ongoing maintenance, which many homeowners do not wish to be carrying out themselves. Whilst the principle of using rammed earth for flooring is sound, in a commercial operation it is often too costly and can provide an unacceptable standard of finish.

Currently we would recommend rammed earth flooring projects to be undertaken by keen DIY builders who have time and are interested in experimenting on a renovation project.

Concrete Floor With Enhanced Finish

At Terra Firma we install concrete floors that are cut and grouted to give a tile like finish. This solution provides the home with an excellent thermal mass, is cost effective and is a very durable and low maintenance flooring material.

For this system of concrete floor we apply several coats of Tung oil just prior to completion of house construction (maximum drying/curing time for concrete). Tung oil provides a clean, non-slip surface finish, which, importantly, allows the concrete to breathe. We also use Iron oxide dyes in the concrete laying stage to create specific floor colourings depending on client specifications.

Poured Earth Tiles

An alternative to the problematic installation of a rammed earth floor is to create and lay poured earth tiles, still more costly than an enhanced finish concrete floor but far more likely to provide an appropriate specification and still maintain the softer richer feel of an earth floor.

Poured Earth Tiles are constructed several months before the expected installation, as they need to cure before use, the general procedure is as follows:

• Extract and sift earth from local site, earth must have some clay content.
• Sifted earth is mixed with 20 – 25 % concrete and polypropylene fibers.
• The mix is poured into 400mm x 600mm tile dividers constructed from non-stick form ply and using a layer of Vaseline as a release agent.
• The tiles are left to dry in the formwork for 36 hours to prevent cracking or twisting, then finished with ‘Tung Oil’ and stacked in a shaded area to cure for 2 months before installation.
• Tiles are laid on a bed of reasonably dry mortar, each tile up to 25 – 30mm apart. We use wide grout lines so that a basic sand and cement mixture is sufficient enough to stop any cracking whilst keeping free of toxic materials.
• As with an enhanced concrete floor we use Tung oil as a water resistant, non-slip, easy clean and breathing surface coating.

For further information on constructing your home using Rammed Earth contact Terra Firma on +64 (09) 963 5942.