Guide · 6 min read
Choosing fastener coatings for African conditions
Matching zinc, hot-dip galvanised, Dacromet and stainless finishes to coastal salt, high UV, mining dust and process chemicals — and what each choice costs you later.
Corrosion is local, not national
A fastener specification that works in Nairobi fails in Mombasa. Distance from the coast, prevailing wind, industrial atmosphere and rainfall pattern set the corrosion category, and that category — not the country — should choose the coating. Within a single project, a coastal elevation and a sheltered internal frame can legitimately carry different finishes.
The practical hierarchy
In rising order of protection and cost: self colour, electroplated zinc, zinc flake or Dacromet, hot-dip galvanised, stainless 304, stainless 316. Hot-dip galvanising is the workhorse for exposed structural fasteners in Africa because 45 to 85 microns of zinc buys decades rather than years, and because it survives handling on site.
Coastal work
Within five kilometres of the coast, plated zinc is a false economy — visible head corrosion appears within a season or two and the client sees it before the engineer does. Specify hot-dip galvanised as a minimum on structural work, Class 4 on roofing, and stainless 316 where the fastener is both exposed and difficult to replace.
High UV and thermal cycling
UV does not attack steel, but it destroys the elastomer in roofing washers and the polymer in nylon fixings. In high-altitude and high-insolation African conditions, bonded EPDM sealing washers are the only sensible choice on roofing screws, and nylon plugs should be UV-stabilised if they will sit exposed before being covered.
Mining, process and chemical exposure
Sulphurous, acidic and chloride-rich atmospheres eat zinc faster than clean coastal air. On plant subject to washdown or process spillage, move to stainless 316 or a duplex grade, and separate dissimilar metals with insulating washers so galvanic corrosion does not do the job that chemistry started.
Two mistakes that repeat
First: mismatching the washer or nut finish to the bolt, so the cheapest component becomes sacrificial and stains the connection. Second: ordering hot-dip galvanised threaded rod with standard nuts — the coating thickens the thread and the nuts will not run. Galvanised assemblies need oversize-tapped nuts, supplied matched.