Building houses in New Zealand often requires backfilling before foundation construction according to different designs and soil conditions.There are many kinds of backfilling materials. What are the backfilling materials that meet the New Zealand standards?What’s the difference between each material?

Gap 7 (General all passing 7mm)

Gap 7 is a small stone particle with a diameter of 7mm that is similar to sand. It is usually used as a leveling material for driveway, foundation before pouring cement, and the main material for backfilling with external water.

Gap 20 (General all passing 20mm)

Gap 20,  is a small stone with a diameter of 20mm that can be used as a leveling material before cement is poured on the foundation of driveway and pavement.The price is high and the application scope is small.

Gap 40/65 (General all passing 45 mm / 65 mm)

Gap 40is a large stone that can be screened by a filter with a diameter of 40mm, and Gap 65, also known as G65, is a large stone that can be screened by a filter with a diameter of 65mm.G40 and G65 are widely used to backfill the foundation of houses. After compaction by rollers, they have high strength surfaces.

Scoria 25/7 (Scoria 25mm-7mm)  & Scoria 50/20 (Scoria 50mm-20mm)

Scoria is made of volcanic stone. It is red in color and has high water permeability. It is mainly used for backfilling of retaining wall and cross-layer drainage pipe.The price is highest.