As shown in the study The Concrete Countertop Institute published in April 2015, dry polymers perform as well as liquid polymers in terms of flexural strength in GFRC. However, the behavior of the mix can differ in important ways that can make working with the mix challenging if you are not familiar with it.
For example, when I first used the Buddy Rhodes GFRC Blended Mix, (which is an all-in-one mix containing sand, cement, dry polymer, pozzolan, and other ingredients) quite honestly, I didn’t like it because it seemed too thick and difficult to work with. The consistency is very different from a Forton liquid polymer mix, and I had trouble adjusting. What I’ve found is that a couple of things are critical to success with this particular mix:
- Pre-dosing a superplasticizer
- Waiting for false set to occur
You may find that mixes using other dry (or liquid) polymers exhibit different behavior. By being aware of the 2 factors above, you can adjust your procedures to work best with your mix.
Recommended Mixing Procedure for Buddy Rhodes GFRC Blended Mix (or Admix)
The order the ingredients are mixed in can have a profound effect on the ease and speed of blending, and quality of the mix. Follow the mixing order outlined below to ensure the mix is blended as thoroughly, quickly and completely as possible. Altering the mix order, or skipping steps may result in a sub-optimal mix that is difficult to blend, may be too stiff (or too runny), and may have poorly mixed ingredients that show up after demolding.
By carefully reading and following the instructions regarding pre-dosing superplasticizer and managing false set, you will be much more successful with this mix.
Note that these instructions also apply if you are using the Buddy Rhodes GFRC Admix and adding your own sand and cement.
- Mix liquid ingredients together (water, ice, liquid superplasticizer)
- Blend all of dry ingredients together (Blended GFRC Mix, pigments, dry superplasticizer)
- Do not blend fibers with the dry ingredients
Either a liquid (e.g Buddy Rhodes WR 420) or a dry (e.g. Buddy Rhodes WR 310) superplasticizer may be added to the pre-mixed ingredients. Choose one or the other based on experience and personal preference.
Superplasticizer Dosing Rates
The following recommended dosing rates are for making a sprayable GFRC mist coat. Use half the recommended dose if a stiffer, hand-packable mix is desired. Adjust dose according to desired consistency.
WR 420 is a powerful liquid superplasticizer optimized and ideal for use in Buddy Rhodes Products. It adds significant workability and fluidity, acts quickly and doesn’t make the mix thick or sticky.
- Recommended dosing rate: 1 mL per 1 lb of GFRC Blended Mix.
WR 310 is a potent dry powder superplasticizer that adds significant amounts of workability and fluidity, but it can make a mix sticky. WR 310 should be first blended into the dry ingredients to ensure good dispersion and to prevent clumping.
- Recommended dosing rate: 0.5 grams per 1 lb of GFRC Blended Mix, or 0.11% dose.
Be sure to have a viscosity modifying admixture, such as Fritz-Pak’s Super Slump Buster, on hand to adjust consistency if your mix becomes too runny. This is especially important with WR 310 because it is so powerful.
See this page for more information on superplasticizers and viscosity modifiers.
- In the empty mixing bucket, add:
- All liquid ingredients
- Half of the pre-blended dry ingredients
- Mix until no dry ingredients remain.
- If PVA or acrylic fibers are to be added to your mist or face coat, add them to the mix now and blend until fully dispersed.
- Add half of remaining dry ingredients and mix until no dry ingredients remain.
- Add remaining dry ingredients and mix until no dry ingredients remain.
- Scrape the sides and bottom of the mixing bucket.
- Mix until all dry ingredients are fully incorporated.
8. Let the mix rest for 10 minutes to allow false set to occur.
9. Re-mix to break false set stiffness before adjusting consistency.
10. Add WR 420 liquid superplasticizer to adjust mix consistency if necessary. Add it 5 mL at a time and mix well before checking.
Add AR Glass Fibers (Only for backer coats)
11. Add AR glass fibers after the mix has been fully blended and adjusted for consistency. Gently mix to just incorporate the fibers into the mix.