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Concrete and GFRC Mix Recipes Concrete Mixing Troubleshooting FAQ
Concrete and GFRC Mix Recipes Concrete Mixing Troubleshooting FAQ
CONCRETE MIX DESIGN RECIPES:
Mix design and recipe formulas are offered here by Expressions LTD as a reference. Expressions LTD is not liable for any results obtained by following mix designs outlined below. Mixes should be tested, and tweaked if desired, at each fabricator's discretion. If you have a recipe you'd like to see featured here, please contact us.


Make sure to check out our 40oz. Mixing Cups (sold here), very useful for all stages of mixing and dosing concrete, additives, and color- in addition to mixing the concrete sealers.

Basic Concrete Countertop Mix: (by Expressions LTD)
  • 1x 80 lb. bag of standard concrete mix (from your local hardware store of choice)
  • 5 lbs. Portland I/II Cement (sold in 94 lb. bags usually, local hardware store)
  • 2 oz. AR Glass Fibers (about a golf-ball sized portion) - SOLD HERE
  • 2 Tablespoons Riteks SP7000 Superplasticizer/Water Reducer - SOLD HERE
  • MIX: Combine 80 lb. bag of concrete with 5 lbs. of Portland Cement and AR Glass Fibers. In clean 5-gallon bucket, add 2 quarts of clean water, and mix in 2 Tablespoons of Riteks SP7000 Superplasticizer. Combine mix water with concrete, and begin mixing. Add small amounts of additional water** until concrete mix resembles that of thick oatmeal.
    • **Some applications may require a drier concrete mix (such as pressing very dry concrete into a form with the goal of creating large voids- to be filled later with a different colored cement slurry), or a wetter mix (filling a vessel sink 2-part sink mold), so adjust the water accordingly.
  • COVERAGE, WEIGHT, and COSTS:
    • Coverage: This mix will product a little above 0.6 cubic feet of concrete. At 1.5" thickness, it will yield roughly 4.8 square feet. At 2" thickness, it will yield roughly 3.6 square feet.
    • Weight: At 1.5" thickness, approx. 21 lbs. per sq. ft. At 2" thickness, approx. 28 lbs. per sq. ft.
    • Costs: Material costs for concrete, cement, fiber, and plasticizer is @$4.10 per bag. This equals out to be $0.85 per sq. ft. at 1.5" thickness, $1.14 per sq. ft. at 2" thickness.
  • Notes: Most standard 80 lb. bags of concrete mix sell for around $3.00, and have somewhere in the vicinity of 15 lbs. worth of Portland Cement in them- the rest is sand and gravel. Increasing the Cement content up to around 20 lbs. is equivalent to the more expensive concrete mix, such as "Quikrete 5000" concrete mix. The main idea behind mixing concrete is to use the least amount of water in order to get the concrete to be workable. The less water used, the stronger the cured concrete will be. Use of additives, such as Plasticizer (also known as Water Reducer) allow the concrete to 'flow' so you can work with it, using less actual water.

Supreme Concrete Countertop Mix: (by Expressions LTD)
  • 1x 80 lb. bag of standard concrete mix (from your local hardware store of choice)
  • 5 lbs. VCAS (Replaces the 5 lbs. of Portland Cement from the Basic Concrete Countertop Mix). - VCAS SOLD HERE.
  • 2 oz. AR Glass Fibers (about a golf-ball sized portion) - SOLD HERE
  • 2 Tablespoons Riteks SP7000 Superplasticizer/Water Reducer - SOLD HERE
  • 2 lbs. Polyplex with mix water prior to combining with concrete. - SOLD HERE
  • MIX: Combine 80 lb. bag of concrete with 5 lbs. of VCAS and AR Glass Fibers. In clean 5-gallon bucket, add 2 quarts of clean water, add in 2 Tablespoons of Riteks SP7000 Superplasticizer, and add the 2 lbs. of Polyplex. Combine mix water with concrete, and begin mixing. Add small amounts of additional water** until concrete mix resembles that of thick oatmeal.
    • **Some applications may require a drier concrete mix (such as pressing very dry concrete into a form with the goal of creating large voids- to be filled later with a different colored cement slurry), or a wetter mix (filling a vessel sink 2-part sink mold), so adjust the water accordingly.
  • COVERAGE, WEIGHT, and COSTS:
    • Coverage: This mix will product a little above 0.6 cubic feet of concrete. At 1.5" thickness, it will yield roughly 4.8 square feet. At 2" thickness, it will yield roughly 3.6 square feet.
    • Weight: At 1.5" thickness, approx. 21 lbs. per sq. ft. At 2" thickness, approx. 28 lbs. per sq. ft.
    • Costs: Average material costs for concrete, fiber, plasticizer, Polyplex, and VCAS is @$11.45 per bag. This equals out to be $2.39 per sq. ft. at 1.5" thickness, $3.18 per sq. ft. at 2" thickness.
  • Notes: Most standard 80 lb. bags of concrete mix sell for around $3.00, and have somewhere in the vicinity of 15 lbs. worth of Portland Cement in them- the rest is sand and gravel. Increasing the Cement content up to around 20 lbs. is equivalent to the more expensive concrete mix, such as "Quikrete 5000" concrete mix. The main idea behind mixing concrete is to use the least amount of water in order to get the concrete to be workable. The less water used, the stronger the cured concrete will be. Use of additives, such as Plasticizer (also known as Water Reducer) allow the concrete to 'flow' so you can work with it, using less actual water.

From Scratch Countertop Mix: (by Expressions LTD)
  • 25 lbs. Portland Cement (Try to use Type I instead of Type I/II for pre-cast)
    • This recipe is good if you want to use White Portland Cement for your mix.
  • 60 lbs of sand/pea gravel. Make sure it's washed so there is no dirt or fine dust. It's okay for the sand to be damp when weighing it. A good starting point is 40 lbs. sand 20 lbs. pea gravel.
    • Consider using quartz sand (it's white) if using White Portland Cement, to help the concrete piece be as white as possible.
  • 2 oz. AR Glass Fibers (about a golf-ball sized portion) - SOLD HERE
  • 2 Tablespoons Riteks SP7000 Superplasticizer/Water Reducer - SOLD HERE
    • Optional (For a stronger, better concrete): Add 5 lbs. VCAS (Replaces the 5 lbs. of Portland Cement, so if adding VCAS you should reduce the Portland Cement in step one to 20 lbs.). - VCAS SOLD HERE.
    • Optional: (For a stronger, better concrete) Add 2 lbs. Polyplex with mix water prior to combining with concrete. - SOLD HERE
  • MIX: Combine sand/gravel in mixer and let mix a few minutes. Add in Portland Cement (and VCAS if using it), and mix (cover mixer if possible to prevent dust messes). Add the AR Glass Fibers and mix just long enough to spread them out. In clean 5-gallon bucket, add 2 quarts of clean water, add in 2 Tablespoons of Riteks SP7000 Superplasticizer (and add the 2 lbs. of Polyplex if using it). Combine mix water with concrete, and begin mixing. Add small amounts of additional water** until concrete mix resembles that of thick oatmeal.
    • **Some applications may require a drier concrete mix (such as pressing very dry concrete into a form with the goal of creating large voids- to be filled later with a different colored cement slurry), or a wetter mix (filling a vessel sink 2-part sink mold), so adjust the water accordingly.
  • COVERAGE, WEIGHT, and COSTS:
    • Coverage: This mix will product a little above 0.6 cubic feet of concrete. At 1.5" thickness, it will yield roughly 4.8 square feet. At 2" thickness, it will yield roughly 3.6 square feet.
    • Weight: At 1.5" thickness, approx. 21 lbs. per sq. ft. At 2" thickness, approx. 28 lbs. per sq. ft.
    • Costs: Average material costs for cement, sand, gravel, fiber, and plasticizer is @$4.25 per batch. This equals out to be $0.89 per sq. ft. at 1.5" thickness, $1.18 per sq. ft. at 2" thickness.
  • Notes: Most Portland Cement bags are 94 lbs. and sell for around $9.00. Sand and Gravel can be purchased at a hardware store, already bagged, for a premium price. The more economical way to get sand/gravel is to get it from a gravel pit, or often times a concrete plant (the guys with the concrete trucks driving around) will let you come buy some very cheap, or give it to you at no cost for small amounts.

GFRC (Glass Fiber Reinforced Concrete) Mix: (by Expressions LTD)
About GFRC:
  • GFRC (Glass Fiber Reinforced Concrete) is lighter, stronger, faster, and cheaper than most typical concrete mixes.
  • GFRC pieces can be de-molded after 24 hours.
  • A Typical GFRC mix 1:1 ratio means One 90 lb. sack of cement and One 100 lb. bag of sand.
  • For many countertop type applications, smaller batches are sufficient, such as 1/4 this amount.
  • The Expressions-LTD Basic GFRC Mix below works great for GFRC countertops, sinks, and furniture pieces.

  • Equipment Needed: 5 Gallon Bucket. Heavy Duty Electric Mixer and Paddle Mixing Blade. Scale. Measuring Cup(s). Hopper Sprayer and Air Compressor. Compaction Roller(s).
    • FACE COAT:
      • Add 6.5 lbs. water (about 3 quarts) to a clean 5 gallon bucket.
      • Add 2.5 lbs. of Polyplex Curing Aid.
      • Add 1 Fl. Ounce of SP 7000 Super Plasticizer.
      • Mix in 23.5 lbs. of #30 Silica Sand (#30 is the sand size, and available at your local hardware store).
      • Mix in 17.5 lbs. Portland Cement (white or gray, available at your local hardware store)
      • Mix in 6 lbs. Vitro Minerals Pozzolans (VCAS).
      • Optional: Mix in any Integral Color, if desired.
      • Add extra water if needed, in small amounts, until mix is creamy.
      • Let mix 'set' (usually about 5 minutes) and then remix briefly.
      • Spray Face Coat of this mix over the mold/form work using a Hopper Sprayer. Face coat should be 1/8" - 3/16" thick.
      • Coverage: It takes about 2 lbs. of the cement mix to cover 1 sq. ft. (which means if you made this batch in this exact size, you could expect around 25-30 sq. ft. of coverage for the face coat)
      • Allow face coat to sit long enough to stiffen, but remain moist (Time varies, usually 30-60 minutes).
    • BACKER LAYERS:
      • Mix another batch, same formula as above.
      • Slowly mix in 1.6 lbs. of 3/4" Length AR Glass Fibers.
      • Hand lay the fiber-rich backer layer mix over the surface of the mold/form at a 3/8" - 1/2" thickness.
      • Use Compaction Rollers to even out this layer, condense, and remove any air pockets.
      • Place a second backer layer, again 3/8" - 1/2" thickness, and compact with rollers.
      • Finished piece should be 3/4" - 1" thick at a minimum.
      • Coverage: It takes about 6 lbs. of the cement mix to cover 1 sq. ft. at around 3/8" thickness (which means if you made this batch in this exact size, you could expect around 8-10 sq. ft. of coverage per backer layer)
      • Additional layers can be added, or a slightly wetter mix can be used last to 'top off' the mold form, and level out the concrete.
    • EXTRA REINFORCING:
      • Extra Reinforcing: Fiberglass Scrim Fabric can be placed between GFRC Backer layers.
      • Fiberglass Scrim will help increase overall strength and flexibility. Ideal for reinforcing around integral concrete sinks.
      • Try to keep Scrim 1/2" away from the Face Coat, to avoid ghosting (faint lines showing an image of something buried in the concrete).
      • A second layer of Scrim can be laid down over the final coat of GFRC, and lightly rolled down into the cement surface.
    • COVERAGE, WEIGHT, and COSTS:
      • Face Coat Batch: Covers approx. 80 sq. ft. at 1/8" thickness.
      • Backer Layer Batch: Covers approx. 30 sq. ft. at 3/8" thickness.
      • Finished GFRC Piece Weight: At 3/4" thickness: 8 lbs per sq. ft. At 1" thickness: 10.5 lbs per sq. ft.
      • Material Cost Approximates: At 3/4" thickness: @$1.99 per sq. ft. At 1" thickness: @$2.65 per sq. ft.
    FAQ for Concrete Mix Problems: If you have a question or answer you'd like to see listed here, please contact us.

    • Problem: Lots of pinholes in concrete or GFRC facecoat using Polyplex in the mix design.
    • Solution: Typically this is the result of mold release, and if spraying GFRC Facecoat; gun pressure settings, spray technique and slump. If Polyplex has been stored in direct sunlight or at high temperatures with the lid off, the de-foamer can evaporate out of the Polyplex, which will result in the air content of the concrete/GFRC mix to rise dramatically. Nine out of ten times, mix temperature ends up getting too hot (above 74 F) causing a rapid loss in slump and pinholes in the concrete surface. Keeping mixes below 74 F, using COLD water and/or ice in the mix to control temperature will help solve this issue. Also, keep the lid on the Polyplex container during mixing, and out of direct sun or hot areas.

    • Problem: When filling pinhole and voids in the concrete using a slurry, the slurry seems to just come off when dry.
    • Solution: Cement Slurry should be mixed so that it is thick like peanut butter, and whenever possible a small amount of plasticizer (such as Riteks SP7000), and Polyplex (about 1 part Polyplex to 5 parts water) should be added to water, and then that water used to mix the slurry until the peanut butter texture. The concrete should be damp prior to applying slurry to it, so it doesn't absorb the moisture from the slurry instantly. Usually too much water will result in slurry that is weak, and will come off when dry.

    • Problem: Lots of pinholes in concrete using a wet-cast recipe.
    • Solution: Completely removing all air pockets and pinholes in a cast concrete piece is near impossible for most applications. To minimize the air pockets, ensure the concrete mixes for 4-5 minutes, or longer, once the correct amount of water is achieved to make the concrete mix like an oatmeal consistency. If the concrete doesn't mix for a while after seeing that consistency, the sand/gravel in the mix may not get fully hydrated by the water, and can trap air. Hydrating the aggregates will help remove air during mixing. And of course, proper vibration of the forms will release and drive air up to the top of the form.

    • Problem: Pinholes in concrete countertops that show up weeks or months after the concrete piece is sealed and installed.
    • Solution: Often times pinholes and voids in the concrete will be just under the surface of a pre-cast concrete piece. They may have a paper-thin coating of cement over them, and normal use of the concrete surface will eventually break that thin cement layer and expose the void underneath. Polishing the concrete surface with diamond pads will expose any lurking voids, but even in cases where polishing the concrete is not desired, a simple quick sanding with 200 grit sandpaper on a palm sander will usually open all hidden voids and pinholes so they can be filled with a cement slurry. Most topical concrete countertop hybrid sealers also bond best to a surface that is honed to a 200 grit, so they can get a good grip to the concrete.