HONEYCOMB COLLAPSIBLE VOID FORMER

Collapsible void former such as Dufaylite® Clayboard, Whiterock® Heave Stopper or Max-Frank Egcovoid® is a recyclable honeycomb cardboard core set between lightweight twin fluted polypropylene or cardboard facings designed to collapse (break down with moisture), creating a void for the ground to heave into. Collapsible boards are filled with water after the design compressive strength of the concrete has been achieved. By doing so, the load-bearing capacity of the board is eliminated. Collapsible void formers, alternatively known as degradable void formers, are constructed from easily degradable materials such as molded paper and corrugated paper. Collapsible void formers also aim to reduce the thickness of concrete, thus decreasing the weight of large concrete structures, such as buildings, bridges, and road infrastructure projects.

When dry, the board is rigid and strong enough to support the weight of wet concrete and steel reinforcement without deflection or creep compression. Water is introduced by 36mm hole diameter void pack pipes or via the connecting hoses of the board to the panel core once the concrete is set. This degrades the honeycomb centre leading to the creation of a void. Hence the name of the collapsing board comes from. Panels will degrade due to moisture absorption and soil bacterial attack, resulting in the formation of a void beneath the slab.

Unlike collapsible sheets, compressible, polystyrene void formers, have a much narrower safe load-fail load window and require the designer to significantly thicken the slab in order to resist the uplift. Anti-heave sheet is 30% smaller than the polystyrene compressible alternatives and requires significantly less ground work to prepare for foundations than the traditional beam and block method and allows for more boards per lorry to be delivered.

It means less soil has to be excavated - this keeps down the muck away costs. In fact, with Clayboard, the void formed is a true void, however sheet can not be used with integral insulation and may introduce methane as the cardboard rots down.

HONEYCOMB VOID FORMER SIZES 

Dufaylite Clayboard® is supplied in panels 2440mm long by 1000mm wide offering coverage of 2.44m2, Whiterock Heave Stopper and Max-frank Egcovoid® formers are manufactured in size 2400mm x 1200mm and standard board coverage 2.88m2. For more information clik here

HOW COLLAPSIBLE FLOOR VOID FORMER WORKS?

Void pack pipe simply “switches off" its compressive strength, taking it from 30kN/m² down to a nominal 3KN/m². This ensures that, when the ground heaves, the board yields with no resistance.

The space accommodates clay expansion without exerting undue pressure on the structure above. The resulting void continues to accommodate natural soil shrinkage and expansion to prevent structural damage. This makes the board an unique product, with its central core designed to collapse under just 3KN/m² once water has been introduced.

The resulting void continues to accommodate natural soil shrinkage and expansion. The board naturally disappears to leave a permanent 100% void with no residual density to pass on heave stresses.

 Clayboard before water is introduced   

Clayboard after water is introduced showing ground heave

HONEYCOMB VOID FORMER COLOURS

Each company has its own colour code. While Dufaylite Clayboard top face is usually black and the bottom face white, Whiterock Heave Stopper comes colour coded: red (60mm), green (110mm) and white (160mm). Max-Frank Egcovoid® Former has off-white colour and its edges must be sealed off using sealing and repair red tape to achieve water tightness.

RESIDENTIAL AND COMMERCIAL GRADES

Collapsible void formers such as Dufaylite are available in two standard strengths, KN30 (Residential Grade) and KN90 (Commercial Grade). On the other hand, Whiterock Heave Stopper being an alternative void former to Dufaylite’s Clayboard, is available in just one maximum strength of 120kn/m2 (good to be used in residential or commercial applications). Max-Frank void former has maximum permissible load for dry panels of 100 kN/m2.

While residential grade is calculated and calibrated for concrete thickness up to 1000mm, commercial grade is used on concrete thicknesses from 1000mm up to 1940mm.

KN30 residential Dufaylite Clayboard has a nominal compressive strength of 30kN/m² when dry and is designed to support the weight of wet concrete up to 1000mm thick (residential grade). KN90 commercial Dufaylite Clayboard has a nominal compressive strength of 90kN/m² when dry and is recommended for concrete slabs thicker than 1000mm. Max-frank Egcovoid® can withstand a maximum loading of 100 kN/m² in dry conditions. Whiterock Heave Stopper Clayboard has one maximum strength of 120kN/m² (residential & commercial grade).

RESIDENTIAL GRADE PRODUCTS (up to 1000mm of concrete)

• DUFAYLITE RESIDENTIAL CLAYBOARD - 30kN/m² - concrete thickness up to 900mm 
• MAX-FRANK EGCOVOID® FORMER - 100kN/m²
• WHITEROCK HEAVE STOPPER - 120kN/m² - concrete thickness up to 900mm

COMMERCIAL GRADE PRODUCTS (above 1000mm up to 1940mm of concrete)

• DUFAYLITE COMMERCIAL CLAYBOARD - 90kn/m²- concrete thickness up to 1940mm
• WHITEROCK HEAVE STOPPER - 120kN/m² - concrete thickness up to 1940mm

COLLAPSIBLE VOID FORMER THICKNESSES

The thickness of product required will be determined by the plasticity index, which is specified by the soil engineer. Varying thicknesses are available and we’ve shown estimated thicknesses below. Generally speaking they are available in 7 thicknesses:

DUFAYLITE® CLAYBOARD - 60mm | 85mm | 110mm | 160mm
WHITEROCK HEAVE STOPPER® - 60mm | 110mm | 160mm
MAX-FRANK EGCOVOID® FORMER - 35mm | 50mm | 100mm 

COLLAPSIBLE  FLOOR VOID FORMER INSTALLATION

The collapsible panels are made from cardboard with a honeycomb cellular core between face sheets and because they are manufactured from cardboard which is glued they can easily cut on site to fit most situations. Void formers must be kept dry prior to use, positioned on a stable, level surface, and shielded with a waterproof membrane. Reinforcement should be appropriately arranged, and concrete should be cast with minimal delay.

Clayboard® panels are safe to handle with no dust and no harmful emissions. Paper honeycomb is delivered direct to site in a weatherproof seal. There are 3 key steps to installing Clayboard: preparation, laying and forming the void.

1.Preparing the site

On arrival, it’s important the product remains dry on site at all times. Remove all water from the foundation zone. Lay a 25mm, flat, dry, level sand blinding. Lay a polythene sheeting (minimum 500g) onto the blinding.

2.Laying the system

Lay the Clayboard, printed face up, making sure the adjoining panels are positioned up closely together. Seal all the joints with Dufaylite Waterproof Tape. Lay polythene (minimum 500g) on top of the Clayboard, overlap and tape all joins and leave an overlap at the edges of the Clayboard. Lay steel reinforcement. Prepare for later introduction of water by using the Clayboard VOIDPAK System. Please note the general rule of thumb is a minimum of one Voidpak per 24m2. The pipe is positioned with the raked end to the Clayboard face. A small cross is cut into the polythene sheet and the top board of each panel and the Voidpak pipe pushed in until the flange is flush with the Clayboard surface. A quarter turn will help lock the pipe in place. The pipe must not penetrate the bottom face of the Clayboard.

3.Forming the void

When the concrete is totally self-supporting, insert a hosepipe and introduce a slow flow of water into the Clayboard. Leave water for approximately 2 hours. After 24-28 hours, strike through the bottom facing of the Clayboard to allow excess water to drain away. Seal the pipe holes with cement or waterproof sealant and make good. The amount of water is approximately 15 to 20 liter/m² depending on panel thickness. The water has to be injected with low pressure and begin with about 20% of the amount.

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