Which Polymer to Use in GFRC Concrete Countertops

I’ve written about the basics of what polymer does in a previous article. I would now like to explain why I recommend a particular polymer, Forton VF-774 originally developed by Ball Consulting and now licensed by Smooth-On.

Most of the following is taken from the original Ball Consulting paper about Forton. I’ve edited it and added a few points that will help you understand how Forton compares to other polymers sold to the concrete countertop industry, as well as removed information that is not relevant to the concrete countertop industry.

Description of Forton

Forton VF-774 has been the GFRC polymer of choice for commercial GFRC producers for many decades, and has a 30 year track record of proven success. It meets PCI specifications for curing admixtures in GFRC.

The two primary and very extensively tested and documented reasons to use Forton VF-774 in the batch are:

  • The elimination of the 7-day wet cure required to achieve the maximum strengths of the GFRC matrix at 28 days.
  • To significantly improve the long-term physical properties of the GFRC composite, especially the aged flexural strain to failure.

In addition to these very important points, there are other points that contribute to a high quality and high performance GFRC product. These reasons are:

  • UV stability of the Forton polymer so that architectural finishes maintain their “as produced” colors.
  • Improved workability of the mix at low water/cement ratios. This further enhances the strength of the cured concrete.
  • Easy spraying of vertical surfaces without having the face mix sag.
  • Complete dispersion of iron oxide pigments for batch-to-batch color consistency of face mixes.
  • Tighter, denser-cured product, which reduces absolute moisture absorption and vapor permeability and significantly reduces the rate of absorption as a function of time.
  • Elimination of crazing and spider cracking in the face mix due to the soft polymer particles in between the cement particle and the sand grain.

When evaluating polymers for GFRC, you should know the following details of the product:

  • Polymer chemistry: Not all white, milky liquids are equal in performance. Many are not UV stabile, nor are they alkali stabile in the high pH cement matrix. Some will re-emulsify after curing if they get wet. Few have the proven track record of Forton.
  • Particle size: This controls the effect of pigmentation and color uniformity batch to batch. If this varies, the same amount of pigment will show a different color in the panel.
  • Molecular weight: Influences the durability of the polymer in the matrix.
  • Polymer solids: You are paying for the amount of polymer solids in the liquid. The higher the polymer solids the better value for your dollar.
  • Defoamer: Contrary to normal precast, you do not want additional air entrained in the GFRC composite. VF-774 contains additional defoamer to maintain a high quality slurry through the rigors of high-shear mixing and spraying.

Description of Forton VF-774

  • Water based, all acrylic co-polymer emulsion formulated to comply with PCI MNL 130, Quality Control Manual, Appendix G for curing admixtures used in GFRC.
  • VF-774 also has long term natural ageing data to verify that its use in GFRC composites improves aged flexural properties.
  • VF-774 can be used in precast concrete to reduce absorption, maintain color uniformity, and reduce or eliminate crazing and efflorescence.
  • It is also used in concrete repair products and bonding agents due to its superior adhesive properties.

Forton VF-774 contains 51% solids by weight.

Storage

  • Forton VF-774 should be stored in a closed container, in a dry environment at storage temperatures between 41°F (5°C) to 86°F (30°C).
  • Storage should be enclosed, out of direct sun light and away from direct sources of heat.

Shelf Life

  • With proper storage conditions the normal shelf life will typically be 9 months.

How to use Forton VF-774 in GFRC

Forton is a liquid polymer that has 51% solids content. That means 10 kgs of liquid polymer contains 5.1 kgs of polymer solids and 4.9 kgs of water. The water in the polymer counts as part of your mix water. Dose the polymer solids portion just as you would dose other admixtures. The CCI GFRC Mix Calculator uses Forton VF-774 as the default polymer and does all of the calculations necessary to achieve the correct polymer solids loading and to achieve a low w/c ratio.

Extensive international studies of GFRC show that a minimum polymer-solids loading of 6% of cementitious weight is required to achieve a 7-day, air-cured strength that is equivalent to a 7-day wet-cured strength. Lower polymer solids loads (1.5%-4%) do not provide these benefits, and air curing GFRC with inadequate polymer loading will result in under-cured GFRC that is weaker, more porous and brittle. Higher doses of Forton further reduce permeability and increase the concrete’s flexibility. Large, thin panels used in wet environments (like shower wall panels) greatly benefit from dosing at 10% or higher. CCI recommends at least 6%. The mix calculators use 6%.

If you do not have the mix calculators, click here for an article that explains how to calculate polymer loads (and also fiber loads) for GFRC.

Forton does NOT contain superplasticizer, which is a significant advantage. This permits higher polymer solids dosing without affecting GFRC’s ability to be sprayed or placed on vertical surfaces. Competing blends that have superplasticizer in them force you to under-dose the polymer in order to make the mix cling to vertical surfaces.

Conclusion

Forton VF-774 is a time-tested, economical and essential ingredient for high-quality GFRC. When used correctly using the instructions above, Forton produces GFRC with high tensile strengths and excellent surface quality without a 7-day wet cure. Purchase Forton and other GFRC ingredients in the CCI online store.

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