Over the past few months we have been testing new soils, the intention is to find a more viable resource suitable for rammed earth in the Auckland region. I now feel confident that we have found a soil that fits the bill. The recent tests we have conducted for compressive strength and shrinkage on a soil type commonly found in the Mangawhai area are very promising.

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.