Geological studies have indicated that unstable expansive soils, often called reactive soils, occur all over Australia and New Zealand.

In simple terms, ‘reactive soil’ refers to the reaction of soil to fluctuating moisture content which affects soil stability. By nature, soil expands, contracts or shifts with a rise or drop in moisture levels. The more reactive the soil, the greater it will shift.

The level of soil reactivity on a piece of land can have a huge influence on a dwelling’s structure for many years. An engineer can test the soil and grade it. 

Soil is graded according to the Australian Standard AS 2870/1996, ranging from stable to problematic.

How Soil Reactivity Affects the Construction of a Home

Soil reactivity is an important consideration when laying the foundation of a home because the type of slab used will be dependent on the soil type and the level of reactivity.

For example, if the soil is dry it will contract. This causes the foundation slab to buckle or sink, playing havoc on the building structure, especially smaller homes.

On the flip side, if a flash-flood or storm causes waterlogging, the slab comes under pressure from the excess moisture and cracks, causing extensive damage to a home.

Void Formers Add Strength and Stability

If a dwelling is being built on a site which has reactive soil type, specific slab or footing designs will be required. Invariably, these often require the use of a void former during the pour.

The function of a void former is to separate concrete slabs from reactive soil which can potentially exert damaging pressure on the structural foundations of a dwelling.

Architects came up with two solutions to fill in the voids.

One solution was to use a void former which could be removed when the building took shape.

The other solution was a void former which could be left in place without damaging the dwelling.

Initially, flexible metal sheets which could be rolled into cylinders were used. The challenge they faced was the difficulty in shaping steel as early versions of void makers were mostly cylindrical. Steel void makers were also very heavy.

Subsequently, void formers were made using EPS foam which was lighter, stronger, able to bear heavy loads and could be left behind instead of being destroyed or removed.

More recently, the construction industry has begun to use honeycomb cardboard void formers. They have a honeycomb cellular core between face sheets and are perfect for most situations as they can easily be cut on the construction site.

Excellent dry strength properties ensure the weight of traffic during construction as well as reinforcement and wet concrete can be supported until the cured concrete gains the required strength to be self-supporting.

Factors to be Considered When Using Honeycomb Cardboard Void Formers

Although honeycomb cardboard void formers are now being widely used, care needs to be extended by contractors to ensure the intended use of the product is met.

The following are some recommendations to take into consideration: 

Preventing Premature Collapse: Cardboard void formers must be dry before use as contact with moisture can lead to degradation. They should not be affected by dampness while storing or transportation. They should be kept away from moisture until the concrete is strong enough to support itself. 

Safe Delivery: Cardboard void formers should be used as soon as they are delivered to minimise exposure to the elements of nature. Care should be taken when handling and transporting cardboard void formers to keep them off the ground, allowing air to circulate and to keep them dry.

Usage: Installation and concrete pouring should preferably be done straight away, preferably on the delivery day. Any delay in time can jeopardise the effective use of the void formers. 

Bar chair Positioning: To avoid puncturing the face sheet, concentrated loading from bar chairs should be spread. Flat based chairs can be used directly on the surface. Wire leg bar chairs will need bar chair plates under them to prevent puncturing of the surface sheets. 

Installation: Use polythene sheeting on the top side of boxes to protect the void former from moisture and the wet concrete. 

The boxes shall be placed close together to prevent concrete from falling between them. Lap the polythene sheets 150mm at joins and tape them. 

The polythene sheet should be pulled down the sides and then across the bottom of beam trenches. Before placing the polythene overlay, slash the poly-wrap around the boxes.

Bar chair plates with a minimum diameter of 200 mm should be under bar chairs. This is required to distribute the reinforcement load before placement of the concrete. 

When pouring concrete, the concrete must be evenly placed over boxes and not heaped in one place to minimise excess loads. Concrete should not be poured from a height exceeding 400-450 mm. 

Applying Construction Loads: When applying construction loads, care should be taken not to damage the boxes by distortion and dislodging of the internal partitions and external covers.

If any boxes get damaged or wet, either during or after installation, they should be replaced straight away. Concrete should never be poured over void formers which are damaged or have become affected by moisture.

Clayform Honeycomb Cardboard Void Former

Clayform Void Former – A Versatile & Eco-Friendly Void Former Solution

Clayform void former is a strong, lightweight and bio-degradable honeycomb cardboard void former, making it significantly more environmentally friendly than foam void formers.

Developed to create space between the soil and the building foundation, Clayform reduces the upward force transmitted to the structure due to ground heave. It has the strength to support the concrete load when it is poured. 

Designed for residential as well as large-scale commercial projects, Clayform is the ideal void former solution for the construction of dwellings located on reactive soil sites. 

Here are six reasons, why Clayform void former is a superior choice:

Strong and Rigid: Ensures high-pressure loading when pouring concrete

Bio-Degradable: Clayform breaks down over time, leaving a genuine void which reduces the risk of reactive soils impacting on the slab or causing structural damage in the future. 

Environmentally Friendly: Made from 100% recyclable cardboard

Damage-Free Packaging: Different packaging options are available to suit the requirements of the construction site.

Australia-Wide and New Zealand, On-Time Delivery: Multiple locations ensures Clayform void formers can be delivered on-time throughout Australia and New Zealand.

Cost-Effective Premium Quality: Australian-made premium quality product that delivers long-term cost efficiencies

Clayform void formers are available in different sizes, thicknesses and can be delivered to the construction site, bagged or unbagged.

Care needs to be taken to select the right product for the type of construction. To find out which product is the most suited to your requirements, please call us on 1300955002 to speak to one of our experts or call click here to contact us with your enquiry.


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