GFRC Fiber Ghosting Explained: How to Embrace the Material and Cast Cleaner Concrete Countertops
"Do not apologize for fiber reinforced concrete. Fiber ghosting is not always a flaw. Sometimes it is the honest signature of GFRC, like grain in wood or chocolate chips in a cookie." -Brandon Gore
Chocolate chip cookies have chocolate chips. Nobody is shocked when they show up on the surface.
GFRC works the same way.
In this episode, we talk about the material reality of fiber reinforced concrete and why some fiber ghosting is a natural part of SCC GFRC. A slight shadow or hint of fiber can be the honest signature of the material, not a defect.
But there is a difference between natural ghosting and fibers truly showing on the surface.
We break down what causes problem fibers to appear, including poor fiber selection, weak mix design, low flow, and improper casting techniques. We also cover practical ways to reduce ghosting while keeping the strength that makes GFRC such a powerful system.
You will learn:
- Why some fiber ghosting should be expected in GFRC countertops and sinks
- The difference between ghosting and exposed fibers
- How fiber type changes surface quality
- Why plasticizer load and flowability matter
- How mold material affects finish quality
- Better placement and consolidation techniques for cleaner casts
- How to balance beauty and strength in decorative concrete
If you want smoother results, fewer defects, and a healthier understanding of the material, this episode will help you work with concrete instead of fighting it.
Kodiak Pro Maker Mix and RADmix were built for makers who want strength, flow, and professional finishes without the guesswork.
#GFRC #ConcreteCountertops #DIYConcrete #DecorativeConcrete #ConcreteSinks #MakerMix #Craftsmanship #ConcretePodcast #SmallBusiness #Makers
TRANSCRIPT SUMMARY:
0:15 - Spring Break, Family, and Making Memories
Brandon and Jon open the episode with a casual catch-up about spring break, family trips, fishing, campfires, and the little moments kids remember most. The conversation sets the tone for the episode: the small details matter, whether you are raising kids or casting concrete.
Highlight: Sometimes the simplest moments become the ones that matter most.
2:45 - Concrete Hero's Quest Workshop in Napa, CA
Brandon announces that more people have registered for Concrete Hero's Quest, happening June 8-10 in Napa, California at SC Fabrication.
This advanced decorative concrete workshop is designed for serious makers, GFRC professionals, and artisans who want to push their skills further. It is not a beginner class, but beginners with strong passion can still gain tremendous value through hands-on learning and community.
Highlight: Concrete Hero's Quest is built for makers who want to move beyond basics and work shoulder to shoulder with other serious concrete artisans.
5:34 - Ramm-Crete Workshop and Future Class Schedule
Brandon explains that Ramm-Crete will not be covered at the Napa workshop because the schedule is already packed. A dedicated Ramm-Crete class may happen later.
He also shares that he sold his current shop, leased it back through the end of the year, and is working on building a new studio. Future Concrete Design School classes will depend on the timeline of that new shop.
Highlight: More workshops are coming, but the schedule depends on the new shop build and transition.
6:54 - ICT Sealer Application and Better Instructions
Jon talks about helping workshop attendees better understand ICT Sealer application, including how to avoid over-sealing or under-sealing.
Brandon adds that Kodiak Pro is working on simplified instructions and PDFs for Fusion, Protect, and Maker Mix. The goal is to make the process easier for makers at every skill level.
Highlight: Better instructions help makers get better results with fewer mistakes.
10:47 - SCC GFRC and Fiber Ghosting
The main technical topic begins with a common issue: fibers showing or ghosting in SCC GFRC.
Brandon and Jon explain that occasional fiber shadowing is part of fiber reinforced concrete. Like chocolate chips in a cookie or grain in wood, it is part of the material, not automatically a defect.
The key distinction is this:
Fiber ghosting is a subtle shadow under the surface.
Exposed white fibers on the surface usually point to poor fiber selection, wrong mix design, or improper casting technique.
Highlight: Do not apologize for fiber reinforced concrete. Some ghosting is the honest signature of GFRC.
14:13 - Embracing Fiber Reinforced Concrete
Brandon explains that he has used SCC GFRC almost exclusively since around 2012 and has never had a client complain about subtle fiber ghosting.
To the client, it reads as concrete. To the maker, it may feel like a flaw only because the maker knows what they are looking at.
Highlight: Many fiber ghosting concerns start in the maker's mind, not the client's eye.
16:22 - Fiber Selection: Ghosting vs Exposed Fibers
Brandon explains that certain flat, feather-like glass fibers can get stuck on the surface and create visible white fibers. That is different from natural ghosting.
Jon adds that the fiber type matters. Thicker, whiter fibers can appear more obvious, while thinner, more translucent fibers may blend better into the surface.
Highlight: If you are seeing actual white fibers on the surface, start by checking your AR glass fiber selection.
20:19 - Plasticizer Load, Water, and Flowability
Brandon and Jon discuss how TBP plasticizer load affects fiber ghosting in SCC GFRC.
Brandon notes that when he uses too much plasticizer, he tends to see more fiber shadows. By backing TBP down to the minimum amount needed for good flow, he sees less ghosting.
They recommend starting around:
6 lbs of water per 50 lb bag
70 grams of TBP
50-55 degrees F mix temperature
Then make one adjustment at a time.
Highlight: Do not change water, plasticizer, and temperature all at once. Dial in one variable at a time.
25:27 - Acid Etching and Surface Exposure
Brandon explains that deep acid etching can expose more sand and more fibers. His preferred approach is a light acid etch to remove the soft cream layer, not a heavy etch that cuts deep into the mix.
His general method:
- Clean with Simple Green
- Rinse the surface
- Use 6 parts water to 1 part muriatic acid
- Apply with a pump sprayer
- Keep the surface wet
- Etch for about 30 seconds
- Rinse and scrub with a clean Scotch-Brite pad
Repeat only if needed
Highlight: It is better to do multiple light acid etches than one aggressive etch you cannot undo.
29:18 - Do You Need to Neutralize Acid Etch?
Brandon and Jon explain that neutralizing is usually not necessary. The alkaline concrete surface neutralizes the acid as it reacts, and thorough rinsing removes residue.
Highlight: Rinse thoroughly, but do not overcomplicate the process with unnecessary neutralizing steps.
30:19 - How to Minimize Fiber Ghosting
Jon summarizes the process:
Cast samples
Monitor water and TBP
Start with 6 lbs of water and 70 grams of TBP
Target 50-55 degrees F mix temperature
Choose the right fiber
Choose your acid etch level
Use shorter, smaller Tex fibers when possible
Highlight: Cleaner SCC GFRC results come from controlling the full system, not chasing one magic fix.
33:18 - Deep Etch vs Smooth Finish
Brandon shares an example from past workshops where very deep acid etching produced a rougher, more exposed surface.
He contrasts that with his preferred look: clean, smooth concrete with very minimal air, a light acid etch, and no slurry.
Highlight: The right finish depends on your brand, your client, and the look you are selling.
38:33 - Mold Material and Fiber Ghosting
Brandon explains that mold material affects fiber ghosting.
Harder mold surfaces like melamine, fiberglass, hard plastic, and Lexan transfer vibration better. This helps air release and can help fibers lift away from the face.
All-rubber molds can deaden vibration, allowing fibers to settle closer to the surface and create more ghosting.
Highlight: If you are getting heavy fiber ghosting, ask yourself what mold material you are casting into.
39:26 - Why Not to Use High-Frequency Vibration with GFRC
Brandon cautions against using traditional concrete vibrators with SCC GFRC. High-frequency vibration can cause fibers to drop out of suspension, which can increase ghosting.
Instead, he recommends light movement:
Sloshing the mix
Tapping the form
Using a rubber mallet
Gently moving the casting table
Highlight: With SCC GFRC, you want controlled movement, not aggressive vibration.
42:27 - Blending Glass Fiber and PVA Fiber
Jon explains that blending glass fiber with PVA fiber can reduce visible glass fiber ghosting. PVA can help create a scaffolding effect that keeps glass fibers from settling as aggressively.
Brandon adds that blending fibers also reduces the total number of glass fibers in the mix, which can help visually.
Highlight: Glass fiber and PVA do not have to be either/or. Blending can be a useful strategy.
45:03 - Make Samples and Set Expectations
Brandon emphasizes the importance of samples. If the sample shows subtle fiber shadowing and the client approves it, then the final sink, countertop, or furniture piece will not surprise them.
He compares it to wood grain in wood or patina on copper.
Highlight: Samples protect the maker and help the client understand the material before the project starts.
47:25 - Confidence, Craft, and the Maker's Mindset
Jon and Brandon talk about the mental side of being a maker. If you use high-end materials, proper techniques, and proven systems, do not talk your own work down.
Confidence matters.
Clients respond to how you present the material. If you apologize for it, they may see a problem. If you embrace it, they often see beauty.
Highlight: Present GFRC with confidence. You chose the material for its strength, performance, and beauty.
52:00 - Ice Loading and Mix Temperature
Brandon shifts into mix temperature and why it matters as the weather warms up.
He recommends monitoring SCC GFRC mix temperature with an IR thermometer and targeting 55 degrees F during slake.
As temperatures rise, makers may need more ice and slight TBP adjustments to maintain the same flow.
Highlight: Many "bad batches" are not bad materials. They are temperature problems.
54:15 - Consistency Across Seasons
Jon explains that the mix will perform consistently season after season if you monitor temperature and make adjustments.
Summer may require more ice and slight plasticizer changes. Winter may require reducing ice and backing down TBP.
Highlight: The best makers do not guess. They measure, adjust, and repeat.
56:13 - Crystalline Silica and Safer Concrete Materials
Brandon discusses growing concern over crystalline silica exposure in manufactured stone and concrete products.
He explains that Kodiak Pro removed crystalline silica dust from its mix design to help create a safer product for makers, shops, and customers.
Jon also raises concerns about powder polymers and respiratory exposure.
Highlight: When you know better, you do better. Safer materials protect your craft, your shop, and your future.
1:04:51 - Mixer Selection for SCC GFRC
Brandon compares barrel mixers and vertical shaft mixers.
For SCC GFRC with a fluid, milkshake-like consistency, he prefers a large barrel mixer because it can handle bigger batches, uses standard power, and cleans faster.
For thick, hand-placed mixes, a vertical shaft mixer like the IMER 360 or 120 may make more sense.
Highlight: Choose your mixer based on the type of concrete you make, not just what someone else uses.
1:10:25 - Sharing Shop Space and Building Community
Brandon talks about working alongside Case in his shop and the benefits of having another maker nearby.
Even though they run separate businesses, sharing space creates efficiency, support, and a stronger creative environment.
Highlight: Like-minded makers are better together. Shared space can create shared momentum.
1:12:34 - Closing
Brandon and Jon wrap up the episode with a reminder that great concrete comes from understanding the material, controlling the variables, and embracing the process.
Final Highlight: GFRC rewards the maker who works with the material instead of fighting it.