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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.
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.
- Allow face coat to sit long enough to stiffen, but remain moist (Time varies, usually 30-45 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.
- 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.
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FAQ for Concrete Mixing 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.
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