Geomet, Dacromet, and Ruspert are widely used corrosion-protective coatings for fasteners, but they differ significantly in coating structure, environmental compliance, hydrogen embrittlement risk, friction control, and suitable applications.
In general: Geomet is a modern, chromium-free zinc-flake coating system. Dacromet is a traditional zinc-flake coating system that normally contains hexavalent chromium. Ruspert is typically a multilayer system consisting of zinc plating, a conversion layer, and a baked ceramic topcoat.
For modern high-strength bolts, controlled tightening, and strict environmental compliance, Geomet is generally the strongest option. For construction screws and self-drilling screws, especially where colour and installation abrasion resistance matter, Ruspert is often attractive. Traditional Dacromet is mainly a legacy specification.
1. Corrosion Performance
Geomet
Geomet normally gives the most predictable high-performance result when the coating grade, coating mass, topcoat, and application process are properly specified. Typical systems include 720 hours neutral salt spray for standard systems, 1,000 hours for more demanding systems, and 1,500-2,000 hours with higher-performance basecoats and compatible topcoats.
It provides both barrier protection from overlapping zinc and aluminium flakes and sacrificial cathodic protection from zinc.
Dacromet
Dacromet can also provide excellent corrosion resistance with a thin coating. Historically, the chromium chemistry provided strong passivation and self-healing behaviour. Typical commercial requirements were often 500 hours without red rust, 1,000 hours for enhanced systems.
Ruspert
Ruspert generally provides very good corrosion resistance, particularly for construction screws. Common commercial classifications are R500 (500 hours), R1000 (1,000 hours), and R1500 (1,500 hours).
2. Environmental and Regulatory Requirements
Modern Geomet is generally the safest choice where the customer requires RoHS compliance, REACH compliance, and hexavalent-chromium-free coating. Traditional Dacromet normally contains hexavalent chromium and is generally unsuitable where RoHS compliance is mandatory. Ruspert compliance is more product- and applicator-specific.
3. Hydrogen Embrittlement
Geomet and Dacromet are non-electrolytically applied zinc-flake systems. When pretreatment uses alkaline cleaning and mechanical blasting rather than acid pickling, hydrogen is not intentionally introduced during coating. They are therefore well suited to property class 10.9 and 12.9 bolts.
The conventional Ruspert system begins with a metallic zinc electroplated layer. Electroplating and acid cleaning may introduce hydrogen. For high-strength carbon-steel components, the supplier should confirm whether acid pickling is used and whether post-plating hydrogen-relief baking is performed.
4. Friction and Tightening Performance
For structural, automotive, and engineered bolted joints, corrosion resistance alone is insufficient. Geomet has a broad range of engineered lubricated topcoats to control the coefficient of friction, torque-tension relationship, and resistance to stick-slip.
Bottom-Line Assessment
- Best overall engineered coating: Geomet
- Best for high-strength fasteners: Geomet (non-electrolytic, controlled friction)
- Best for self-drilling and construction screws: Often Ruspert
- Least suitable for new environmentally compliant specification: Traditional Dacromet