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.
GFRC (Glass Fiber Reinforced Concrete) Mix: (by Expressions LTD)
- 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).
- 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).
- 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: 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.