What Is Blanc fixe?
Blanc fixe (French: "permanent white") is synthetic precipitated barium sulphate (BaSO₄), produced by chemical precipitation from barium chloride and sodium sulphate solutions. Unlike natural barite mined from ore, blanc fixe offers tightly controlled characteristics:
- Particle size D50: 1–3 µm
- Brightness: 95–98% (ISO 2470)
- Purity: ≥ 98% BaSO₄
- Density: 4.3–4.5 g/cm³
- Suspension pH: 6.5–8.0 (neutral)
Epoxy coating and floor manufacturers use only blanc fixe — natural barite's coarse particle distribution makes it unsuitable for thin-film systems.
Key Properties: Comparison Table
| Property | Blanc fixe | Natural barite | Chalk (CaCO₃) | Talc |
|---|---|---|---|---|
| Density, g/cm³ | 4.3–4.5 | 4.2–4.5 | 2.6–2.8 | 2.7–2.8 |
| D50, µm | 1–3 | 5–50 | 2–15 | 3–20 |
| Brightness, % | 95–98 | 85–92 | 90–96 | 80–90 |
| Acid resistance | High | High | Low | High |
| UV stability | High | High | Medium | Medium |
| Recommended for epoxy | ✔ Yes | Coarse systems only | ✖ No | Limited |
Why Add Blanc fixe to Epoxy?
1. Cost Reduction — 30–45%
KER 828 epoxy resin costs 8–12× more than blanc fixe. Adding 100–150 phr filler reduces the finished coating cost by 30–45% with minimal impact on mechanical performance.
2. Improved Thixotropy and Self-Leveling
Fine BaSO₄ (D50 1–3 µm) creates a structured network in the liquid matrix. This improves thixotropy: the compound resists sagging on vertical surfaces, but levels smoothly when applied with a squeegee or spike roller.
3. UV Stability
BaSO₄ is chemically inert to UV radiation. Unlike chalk and organic fillers, blanc fixe does not accelerate photodegradation of the epoxy matrix — coatings retain colour and gloss longer.
4. Better Hiding Power
High refractive index (n = 1.64) combined with fine particle size creates a light-scattering effect. Coatings with blanc fixe have better hiding power with less pigment paste.
Dosage for Different Epoxy Systems
| Application | Dosage, phr | Notes |
|---|---|---|
| Self-leveling floor 2–3 mm (KER 828) | 100–150 | Optimal range for flow and leveling |
| Self-leveling floor 3–5 mm (pour coat) | 150–200 | + quartz sand 300–500 µm |
| Thin-film topcoat | 30–60 | Above 60 phr → matte surface |
| Anti-corrosion primer | 20–40 | Combined with zinc dust |
| Wall protective coating | 50–80 | + TEGO AIREX 900: 0.3 phr |
Note: above 160 phr, viscosity spikes sharply and the mix loses its self-leveling ability. A reactive diluent (RDE, 5–10 phr) can compensate if higher filler loading is required.
Mixing Order
- Dry the filler: blanc fixe moisture ≤ 0.3%. If stored in an open container — dry at 80°C for 2 hours.
- Mix resin and hardener: combine KER 828 and KH-816 (100:27 by weight), stir 1 min at 500 rpm.
- Add blanc fixe: add gradually while mixing at 300–500 rpm.
- Disperse: mix 3–5 min until all agglomerates disappear.
- Add pigment: introduce pigment paste last, disperse 2 min.
Typical Self-Leveling Floor Formulation (per 1 kg mix)
| Component | Mass, g | % of mix |
|---|---|---|
| KER 828 (epoxy resin) | 290 | 29.0% |
| KH-816 (hardener) | 78 | 7.8% |
| Blanc fixe (BaSO₄) | 580 | 58.0% |
| TEGO AIREX 900 (defoamer) | 3 | 0.3% |
| Pigment paste | 49 | 4.9% |
Why Chalk (CaCO₃) Must Not Be Used
Chalk is not suitable for industrial epoxy coatings:
- Acid reaction: CaCO₃ + H₂SO₄ → CaSO₄ + CO₂↑ + H₂O. The released CO₂ causes blistering and delamination.
- Alkaline pH 8.5–9.5 accelerates epoxy chain hydrolysis.
- UV yellowing and colour instability.
BaSO₄ has none of these drawbacks: neutral pH, no acid reaction, stable colour.
