Not all GFRC is Created Equall

Three Ways To Be Cheated When Your Vendor Supplies GFRC - Not All GFRC Is Created Equal....

It is a "Buyer Beware World" out there in the land of "Price and Delivery Marketing." There are some guidelines to help keep you out of trouble when the note on the drawing simply says "GFRC."

1. Short Fibers

This is the most likely way you may be cheated on non-structural architectural products - the vendor uses short strand fibers (1/4 or 1/2 inches in length).

This is done because it can be added to conventional precast concrete just before the mix is poured into the mold. This actually requires some critical attention to detail or the glass will be there, but not in a form that adds much to the matrix strength.

Specifically, if the fibers are not handled properly, the strands will come apart and be hundreds of hair-like glass filaments which have no strength. What happens when a rope is unraveled? Do the individual cords collectively have the strength of the woven hawser? No, they have no strength unless they are maintained in the collective bundle where they reinforce one another under load. The whole (fiber strand) is much stronger than the sum of the strength of the parts (filaments).

The fundamental problem revolves around how to get a uniform distribution of glass fibers without causing the fiber strand to break into filaments during the mechanical mixing.

This requires special mixing equipment. Ask your intended vendor if they ever have a problem with filamentation. If they tell you the TV reception has been great since the cable was put in... or they haven't ever had fungus under their toenails... If they tell you stuff like that, hang up and call 1-800-356-2462.

The technique and method are totally different to manipulate the 1 1/2 inch long fiber which is used by STONEWEAR - obviously it requires more skill and equipment or everyone would do it because the material cost is the same by weight.

2. Fiber Content by Weight

Since the glass costs the same regardless of the length, it is very tempting to reduce the amount of glass in the mix because it is by far the most expensive component. Glass constitutes around 60% of the material cost in GFRC.

The graph summarizes the hazards of relying on a simple generic specification like "GFRC." Chart

Both products indicated on the graph are GFRC. The variables are:

1. Length of fiber strand

2. Amount of glass as a percent of total mix by weight.

What can be deduced from this quantified information?

1. The long strand 1-1/2 inch version of GFRC is THREE TIMES STRONGER than the short 1/2 inch fiber.

2. The strength of GFRC varies dramatically with the actual glass content. Reduce the glass content from 4% to 2% (thus reducing the material expense by 30%) and lose half the strength in a long strand fiber product.

3. Type of Glass

All glass fiber provides dramatic strength increase to the cement mortar matrix for the first year or so. Only the special, expensive, AR Glass (Alkaline Resistant) provides the longevity in strength and usefulness required in bona fide GFRC products.

How can I tell what I got?

From a practical standpoint, you can’t unless you have a very well equipped forensic material science laboratory at your disposal. You have to rely on the integrity of your vendor.

How can I be sure of what I am going to get?

You can’t! Obviously, that is what specifications are supposed to do, but in practice a little information will go a long way toward protecting you from purchasing product with loosely defined material requirements. Use the information provided on this page to ask informed questions in your price and delivery search. Remember, not all GFRC is created equally.

Clearly, it is a case of buyer beware - choose an experienced material supplier who can answer your questions about fiber length, glass content, and glass type.

Stonewear is the pioneer and market leader in this material technology. Since 1976, we have focused over twenty years of continuous product and technique development on using long strand fibers to fabricate unique three-dimensional shapes.

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