Need tech help with a workshop?

Cement: No two cements are the same, they have different mineralogies and different particle sizes. Cements from the same kiln will have a different particle size depending on the date and time of year made. Basically, finer particle size will increase the surface area and the plasticiser demand.

• Finer particle size will increase thixotropy, the amount of flow when being agitated. A higher thixotropy produces much less flow when not agitated.

• Sand: The size of your sand has a huge effect on the flow of your GFRC, a coarse sand will have a better flow than a fine sand. If your sand is very fine, it could make your mix unusable and solid. A coarse sand will have a lower water demand than a fine sand, and a wet sand has trapped water on the surface compared with dried sand. Controlling your mix, you should always take into account the level of water in your sand. To do this either use dried sand or dry your sand before you weigh it out.

• Temperature: The hydration of cement gets faster with increasing

temperature, roughly halving the work time every 10°C rise.

• Therefore, if the cement gels at 2 hours at 20°C, it will gel at about 1 hour at 30°C and 30 mins at 40°C. Adding ice changes the mix temperature and slows the get down, so always check your water and powder temperature.

Amount of ice to add for any temperature. Always subtract the ice from your mix water.

10 kg of water with 50% ice would be 5kg water and 5 kg ice.

Note: If adding Ice, only add half your powder to the water/ice first to allow some of the ice to melt before adding the rest of the powder. Otherwise, your mix may gel prematurely.

MACt Premix is a general 100+ MPa GFRC mix. It is constructed from very high whiteness Portland cement, a specific washed and dried white sand of optimum particle size. These are blended with the specialist polymers, hydration modifiers and super plasticisers at accurately controlled levels. It is a complete, professional grade GFRC mix. Coverage per bag -½ sqm @20mm thick.

Typical additional admixtures levels for a 20kg:

• Water: 2.78L–3.0L
• Plasticiser: 10g – 50g
• Fibres HD: 50g-300g
• Fibres Bundled: 400g-700g
• Retarder: 5g-20g
• Accelerator: 5g–20g
• Defoamer: 1g-3g
• Colour: up to 800g

*NOTE: All admixes will alter the way the mix behaves.

City Mix has developed a unique and economical technology that enables the recycling of large volumes of waste packaging and insulating foam (commonly “EPS”) into an extraordinarily lightweight and user-friendly material suitable for blending in a wide variety of concrete products. The patent-pending technology allows varying portions of the heavy sands and gravels common to cement-based mixtures to be replaced with ultra-lightweight City Mix material in order to reduce overall concrete product weight.