This article contains detailed concrete countertop mix recipes for GFRC. You should understand the basics of what GFRC is. If you are not familiar with GFRC, please see this article.
Before we give a specific mix recipe, it is important to understand several principles of concrete countertop mix design. This comprehensive article covers:
Principles of GFRC Concrete Countertop Mix Design
GFRC typically uses a fiber-free “mist” or “face” coat that is applied to the visible surface of the forms, followed by a fibrous “backer” coat. The mist/face and backer coats should all use the identical base mix design.
The main ingredients of your mix are sand, Portland cement, admixtures such as Integrity PowerPack, water, and AR glass fibers. If you are using Integrity PowerBlend, you simply add water and AR glass fibers.
The total cementitious material (TCM) represents the weight of the reactive ingredients in the mix: Portland cement plus the pozzolans in the Integrity PowerPack or PowerBlend. The TCM is reported for each of the mix recipes. This is very important for dosing fibers, any additional admixtures, and pigments.
The proportions of the first three main ingredients (Sand, Cement, PowerPack) are important. They have been very carefully selected to produce the strongest concrete possible. Do not change the ingredient proportions of sand, cement or PowerPack in the recipes below. If you are using PowerBlend, these proportions are already set in the mix.
Two other important ingredients that may be varied within a reasonably narrow range are the amount of water in your mix and the AR glass fibers.
– Water cement ratio: w/c = 0.30. Water is a very important ingredient that must be dosed carefully. Click here for more information about what w/c means and the importance of water in concrete.
- A w/c of 0.30 is a good starting point. Vary w/c as needed within the given range. Try increasing it by 0.01 if your mix is a bit stiff or reducing it by 0.01 if your mix looks too wet. The maximum allowable w/c is 0.32.
– Fiber dose: Add to the backer coat 2.5% AR glass fibers by weight of total material. This includes water, pigment, and all other ingredients. Click here for more information about how fibers are dosed in GFRC.
- For lightweight, low-stressed decorative pieces, the fiber content may be reduced to 2% (but no less), and for high stress pieces, it may be increased to 3%.
- Using fewer fibers increases flowability but reduces strength, and it makes your concrete more brittle and fragile. Adding too many fibers (more than 3%) often reduces both flowability and strength because the extra fibers make good compaction difficult, trapping air voids in the concrete that reduce strength.
Other ingredients, like pigments and superplasticizer, can be varied the most. Pigments can have a useful range of 0% to 6%. Integrity UltraFlow superplasticizer has a useful range of 0% to 0.85%.
- Pigments and superplasticizer are always dosed based on total cementitious weight. For example, if the TCM amount is 10 kg, and the UltraFlow dose is 0.50% (equal to 0.005), then the amount of UltraFlow required would be 0.005 x 10 = 0.05 kg (or 50 grams). The TCM for each mix recipe is shown below.
Techniques for Casting GFRC
While commercial GFRC uses a spray-up method that requires expensive equipment, in the concrete countertop industry pros use various techniques for casting GFRC.
- The direct cast method of making GFRC is popular with concrete countertop professionals. They mix the AR glass fibers directly into concrete and simply pour the concrete into the molds at the total desired thickness of the piece.
- For the direct cast method, recipes in terms of volume are most useful. This is because you must plan to fill your forms full to make solid concrete. Volume-based recipes are also useful for sizing your batches and planning your project ingredient amounts.
- The hybrid method for GFRC involves spraying or placing a fiber-free “mist” or “face” coat onto all visible surfaces of the molds, and then hand applying or spraying a fibrous “backer” coat. A mist coat is typically about 1/8″ thick, while a face coat is a bit thicker. The main thickness of the finished piece is due to the backer coat, which is typically made 3/4″ thick.
- For the hybrid method, recipes in terms of area (square footage or square meters) are most useful.
Choosing which method to use depends on many factors, including the final look of the piece, the shape of the molds, what equipment you have, and personal preference. Sometimes projects could be cast using either method, while other projects require a certain method.
Note that our PowerPack Kits and PowerBlend Kits contain ingredients in the correct proportions. This allows you to follow the recipes below with minimal waste of materials.
Concrete Countertop Mix Recipes for GFRC
The following recipes use exactly the same ingredient proportions but have different batch sizes depending upon your needs. Note the area of concrete in square feet and the volume in cubic feet each recipe will make. This is useful for splitting up your project into manageable batches.
Each recipe is given for Integrity PowerBlend, an all in one concrete countertop mix that you just add water and fibers to, and also for Integrity PowerPack, the admix version of PowerBlend that you use with your own sand and cement.
Recipes using English measurements are listed first, followed by all of the recipes in metric units. Click here to jump to the metric recipes.
Direct Cast GFRC: Volume Based Recipes, English
The following 3 recipes give proportions for 1 bag, a 5-gallon bucket, or 1 cubic foot.
This recipe is based on 1 bag of Integrity mix:
Integrity PowerBlend: 1 45-lb bag
| Integrity PowerBlend – 45.00 lb |
| Water (w/c = 0.30) – 6.63 lb |
| AR Glass Fibers 19mm (2.5%) – 1.32 lb |
| Total Cementitious Material: 22.11 lb |
| Total Concrete Weight: 52.96 lb |
Makes
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Integrity PowerPack: 1 30-lb bag
| Sand – 122.95 lb |
| Portland cement – 97.25 lb |
| Integrity PowerPack – 30.00 lb |
| Water (w/c = 0.30) – 36.88 lb |
| AR Glass Fibers 19mm (2.5%) – 7.36 lb |
| Total Cementitious Material: 122.95 lb |
| Total Concrete Weight: 294.45 lb |
Makes
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This recipe makes a volume of concrete that can easily be mixed in a 5-gallon bucket:
Integrity PowerBlend: The one-bag mix can easily fit in a 5-gallon bucket.
Integrity PowerPack:
| Sand – 20.50 lb |
| Portland cement – 16.20 lb |
| Integrity PowerPack – 5.00 lb |
| Water (w/c = 0.30) – 6.15 lb |
| AR Glass Fibers 19mm (2.5%) – 1.25 lb |
| Total Cementitious Material: 20.50 lb |
| Total Concrete Weight: 49.10 lb |
Makes
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This recipe makes 1 cubic foot of concrete:
Integrity PowerBlend:
| Integrity PowerBlend – 117.60 lb |
| Water (w/c = 0.30) – 17.34 lb |
| AR Glass Fibers 19mm (2.5%) – 3.46 lb |
| Total Cementitious Material: 57.79 lb |
| Total Concrete Weight: 138.40 lb |
Makes
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Integrity PowerPack:
| Sand – 57.62 lb |
| Portland cement – 45.58 lb |
| Integrity PowerPack – 14.06 lb |
| Water (w/c = 0.30) – 17.28 lb |
| AR Glass Fibers 19mm (2.5%) – 3.45 lb |
| Total Cementitious Material: 57.62 lb |
| Total Concrete Weight: 138.00 lb |
Makes
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Hybrid GFRC: Area Based Recipes, English
The following four recipes make enough concrete to cover 10 square feet of forms. If your forms are bigger or smaller than 10 square feet, simply scale all of the numbers in each recipe by that amount.
Example: Your forms are 25 square feet.
-
- You need to use a scaling factor which is found by dividing the area of your forms by 10 square feet: 25 / 10 = 2.5.
- You would then multiply each ingredient weight in the recipe by the scaling factor (2.5 in this case).
- The amount of sand for a mist coat would be 6.17 lbs * 2.5 = 15.43 lbs, Portland cement = 4.88 lbs * 2.5 = 12.20 lbs, Integrity PowerPack = 1.5 lbs x 2.5 = 3.75, and water = 1.85 lbs * 4.63 lbs. This makes a total of 36.0 lbs of mist coat.
This recipe makes 10 sq ft of Mist Coat @ 1/8” thick:
Integrity PowerBlend:
| Integrity PowerBlend – 12.56 lb |
| Water (w/c = 0.30) – 1.85 lb |
| Total Cementitious Material: 6.17 lb |
| Total Concrete Weight: 14.41 lb |
Makes
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Integrity PowerPack:
| Sand – 6.17 lb |
| Portland cement – 4.88 lb |
| Integrity PowerPack – 1.5 lb |
| Water (w/c = 0.30) – 1.85 lb |
| Total Cementitious Material: 6.17 lb |
| Total Concrete Weight: 14.41 lb |
Makes
|
This recipe makes 10 sq ft of Backer Coat @ 3/4” thick:
Integrity PowerBlend:
| Integrity PowerBlend – 73.47 lb |
| Water (w/c = 0.30) – 10.83 lb |
| AR Glass Fibers 19mm (2.5%) – 2.16 lb |
| Total Cementitious Material: 36.10 lb |
| Total Concrete Weight: 86.46 lb |
Makes
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Integrity PowerPack:
| Sand – 36.00 lb |
| Portland cement – 28.48 lb |
| Integrity PowerPack – 8.78 lb |
| Water (w/c = 0.30) – 10.80 lb |
| AR Glass Fibers 19mm (2.5%) – 2.16 lb |
| Total Cementitious Material: 36.00 lb |
| Total Concrete Weight: 86.22 lb |
Makes
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Direct Cast GFRC: Volume Based Recipes, Metric
The following 3 recipes give proportions for 1 bag, a 5-gallon (23-liter) bucket, or 1 cubic foot (0.0283 cubic meters).
This recipe is based on 1 bag of Integrity mix:
Integrity PowerBlend: 1 45-lb (20.412-kg) bag
| Integrity PowerBlend – 20.412 kg |
| Water (w/c = 0.30) – 3.009 kg |
| AR Glass Fibers 19mm (2.5%) – 0.601 kg |
| Total Cementitious Material: 10.030 kg |
| Total Concrete Weight: 24.021 kg |
Makes
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Integrity PowerPack: 1 30-lb (13.608-kg) bag
| Sand – 55.770 kg |
| Portland cement – 44.114 kg |
| Integrity PowerPack – 13.608 kg |
| Water (w/c = 0.30) – 16.729 kg |
| AR Glass Fibers 19mm (2.5%) – 3.339 kg |
| Total Cementitious Material: 55.770 kg |
| Total Concrete Weight: 133.558 kg |
Makes
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This recipe makes a volume of concrete that can easily be mixed in a 5-gallon (23-liter) bucket:
Integrity PowerBlend: The one-bag mix can easily fit in a 5-gallon (23-liter) bucket.
Integrity PowerPack:
| Sand – 9.299 kg |
| Portland cement – 7.348 kg |
| Integrity PowerPack – 2.268 kg |
| Water (w/c = 0.30) – 2.790 kg |
| AR Glass Fibers 19mm (2.5%) – 0.567 kg |
| Total Cementitious Material: 9.299 kg |
| Total Concrete Weight: 22.271 kg |
Makes
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This recipe makes 1 cubic foot (0.0283 cubic meters) of concrete:
Integrity PowerBlend:
| Integrity PowerBlend – 53.344 kg |
| Water (w/c = 0.30) – 7.864 kg |
| AR Glass Fibers 19mm (2.5%) – 1.569 kg |
| Total Cementitious Material: 26.213 kg |
| Total Concrete Weight: 62.777 kg |
Makes
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Integrity PowerPack:
| Sand – 26.138 kg |
| Portland cement – 20.675 kg |
| Integrity PowerPack – 6.378 kg |
| Water (w/c = 0.30) – 7.840 kg |
| AR Glass Fibers 19mm (2.5%) – 1.565 kg |
| Total Cementitious Material: 26.138 kg |
| Total Concrete Weight: 62.596 kg |
Makes
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Hybrid GFRC: Area Based Recipes, Metric
The following four recipes make enough concrete to cover the equivalent of 10 square feet of forms (0.929 sq m) . If your forms are bigger or smaller than 10 square feet, simply scale all of the numbers in each recipe by that amount.
Example: Your forms are 25 square feet.
-
- You need to use a scaling factor which is found by dividing the area of your forms by 10 square feet: 25 / 10 = 2.5.
- You would then multiply each ingredient weight in the recipe by the scaling factor (2.5 in this case).
- The amount of sand for a mist coat would be 6.17 lbs * 2.5 = 15.43 lbs, Portland cement = 4.88 lbs * 2.5 = 12.20 lbs, Integrity PowerPack = 1.5 lbs x 2.5 = 3.75, and water = 1.85 lbs * 4.63 lbs. This makes a total of 36.0 lbs of mist coat.
This recipe makes 10 sq ft of Mist Coat @ 1/8” thick:
Integrity PowerBlend:
| Integrity PowerBlend – 5.697 kg |
| Water (w/c = 0.30) – 0.839 kg |
| Total Cementitious Material: 2.799 kg |
| Total Concrete Weight: 6.536 kg |
Makes
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Integrity PowerPack:
| Sand – 2.799 kg |
| Portland cement – 2.214 kg |
| Integrity PowerPack – 0.685 kg |
| Water (w/c = 0.30) – 0.839 kg |
| Total Cementitious Material: 2.799 kg |
| Total Concrete Weight: 6.536 kg |
Makes
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This recipe makes 10 sq ft of Backer Coat @ 3/4” thick:
Integrity PowerBlend:
| Integrity PowerBlend – 33.325 kg |
| Water (w/c = 0.30) – 4.912 kg |
| AR Glass Fibers 19mm (2.5%) – 0.980 kg |
| Total Cementitious Material: 16.376 kg |
| Total Concrete Weight: 39.218 kg |
Makes
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Integrity PowerPack:
| Sand – 16.329 kg |
| Portland cement – 12.918 kg |
| Integrity PowerPack – 3.983 kg |
| Water (w/c = 0.30) – 4.899 kg |
| AR Glass Fibers 19mm (2.5%) – 0.980 kg |
| Total Cementitious Material: 16.329 kg |
| Total Concrete Weight: 39.109 kg |
Makes
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