Frequently Asked Questions

Welcome to the FAQ page for our GFRC products! We understand that when it comes to working. We understand that when it comes to working with GFRC, you may have a lot of questions and uncertainties. We’ve been there too! That’s why we’ve compiled a list of some of the most common questions that we receive from our customers, so you can get the answers you need to make informed decisions about your project.

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Our team of experts is here to help guide you through the world of GFRC with confidence. Whether you’re a professional contractor or a DIY enthusiast, we know that every project is unique and that you want to get it right. That’s why we’re passionate about providing the best products and advice to help you achieve your goals.

As GFRC enthusiasts ourselves, we’ve spent years honing our craft and working with the best products in the industry. We’ve seen it all, from tricky installations to unexpected challenges, and we’re always here to help you navigate any situation you may encounter.

So take a look through our FAQ page and see if we can help answer any questions you have about our GFRC products. And if you don’t find what you’re looking for, don’t hesitate to get in touch with us. We’re here to help and we love talking about all things GFRC.

We’re committed to making your experience with GFRC as smooth and successful as possible, so don’t hesitate to reach out to us with any questions or concerns. Thank you for considering our GFRC products, and we look forward to hearing from you soon!

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.
This is the binder that changes your mix from a paste to a solid. It is the total of both the cement and any pozzolan that you have in the mix. Depending on what you need, some mixes can have very high cementitious contents.
You can pour the benchtop without spraying a face coat. These days it is becoming more popular to pour a Self Consolidating Mix. When using a SCC mix it is recommended to add additional HD fibres into the mix. If you are pouring, we recommend adding an additional 100- 300 grams of 3/6/12mm HD fibres per 20kg mix. If you want better flow in these mixes, use a shorter bundled fibre. MACt SCC Professional Series Premixes have fibre contents well above this, but can still be poured to give perfect mould filling and reduced entrapped air. More technical mix designs can have more complex fibre designs which can give much higher flexural performance. On average, the longer your fibres the higher the flexural strength, but the lower flow of the mix. When SCC mixes are poured fibres aren’t visible in the finished product which is why we no longer need to spray a face coat to hide fibres. In a pourable mix we still recommend putting in Scrim half way through the pieces. This will add additional strength to the mix.
Minimum thickness for any GFRC pieces is 20mm. From experience, we have found that when making GFRC pieces, going thinner then 20mm is when you are very likely to have failures in your products. The thinner you go the more reinforcing you need in a piece to ensure the structural integrity.

The amount of colours that you can create in infinite. We always recommend making up samples to make sure that the colour is what you desire before trialing it on a big piece.

All oxides essentially work the same way. Add in a little and you get a pale colour add a lot and you will have a more concentrated colour. As oxide is a filler when you start adding bigger amounts it will affect your mix, you may need to use more plasticiser to combat this. If you are really chasing that super strong colour, we would then recommend tinting the sealer with Versa colour, this is normally added in the first primer coat. This will really enhance the colour of the piece and make it vibrant.

For example, around 5 grams of deep red oxide into our white premix bag will give you a soft pink colour. For pastel colours look at dosing your colour at 0.1-0.3%

A good starting point for the standard grey colours would be:

  • Light Grey – 50g
  • Standard Grey – 100g
  • Charcoal – 493g
  • Black – 788g
Terrazzo mixes are becoming very popular. When adding aggregates, we suggest adding 20% aggregate to the mix. Higher dosages you will lose some strength and with very high doses of aggregate finished strengths will be greatly reduced. Adding large aggregates to the piece will require the piece to be thicker. A rule of thumb is that the finished piece should be 3½ times thicker than the largest aggregate used. If you are going to grind 3-5mm off your piece to expose your aggregate, you need to add that on to the 3½ times thickness. So, using 10mm aggregate you need to be casting 40mm pieces.

Portland cement is made up of four different minerals, depending on what you need the cement to do you can add different accelerators to achieve different effects.

Some accelerators effect the 1st phase and make the set much quicker and give higher very early strength gains. Some accelerate the 2nd phase accelerate the later strength gains.

MACt can supply both the initial set accelerator or the post final set accelerator. Make your GFRC do what you want it to do.


Blended powder hardener / accelerator admixture formulated specifically for the production of high-performance thin section concrete:

  • Allows the tailoring of the strength gain to your production schedule.
  • Allows the mix to have a long work time of several hours and then have a high 1 day strength to allow de-moulding of the piece.
  • Delivers excellent results in normal and cool conditions where very high next day strengths are required
  • Curing times and heat requirements are significantly reduced while early concrete quality is improved.
  • Does not contain calcium chloride or any other intentionally added chlorides and will not initiate or promote the corrosion of reinforcing steel
  • Less chance of warpage, curling, or cracking
  • Increases strength gains as much as 50% overnight over normal hydration


Depending on the effect you need, the dosage can be selected to suit you and your needs.

Over years of trial and error we found the ceramic sanding pads work the best, give the best finish and also last much longer than a traditional paper sanding disk.

We always recommend having grits from 80 grit up-to 240 grit. The most commonly used disks will be a 120 grit and a 180 grit.

Tip- When pads grits start wearing away, those pads can then be used as a finer grit. For example: A worn 80 grit can be used as a 180 grit.

More question?

Don’t hesitate to get in touch with us! We are here to answer any questions you may have and help you find the right solutions to meet your needs. You can reach us via phone, email, or by filling out the form on this page.