Material pairing and galvanic corrosion
The phenomenon
Section titled “The phenomenon”When two different metals touch in the presence of moisture, an electrochemical cell forms: the less noble metal dissolves, that is, corrodes faster. This is galvanic corrosion.
Three conditions are needed: dissimilar metals, direct contact, and an electrolyte — typically moisture. If any one is missing, the process does not start.
Why it matters for LGS
Section titled “Why it matters for LGS”Because many metals meet in the structure: galvanised profile, screw, rivet, bracket, sheet-metal component, pipework, sometimes copper.
In a dry internal structure the risk is small. Where moisture can reach — external junctions, the connection to the foundation, a ventilated facade, roof trim — it is a real question.
What to watch
Section titled “What to watch”The fastener
Section titled “The fastener”The screw must have corrosion protection matched to galvanised steel. An unprotected steel screw in galvanised sheet corrodes quickly in the presence of moisture, and the corrosion product damages the sheet as well.
Copper nearby
Section titled “Copper nearby”Copper and galvanised steel are a distinctly bad pairing with moisture. Runoff from copper roofing or a copper pipe onto a galvanised surface causes severe corrosion.
Aluminium contact
Section titled “Aluminium contact”Aluminium against galvanised steel in a damp environment is also risky; there a separating layer or a suitable fastener is needed.
Fresh concrete and mortar
Section titled “Fresh concrete and mortar”The strongly alkaline reaction attacks the zinc layer. At the connection to the foundation this is why the separating damp-proof layer matters — and it is needed for ground moisture anyway.
Chemically treated timber
Section titled “Chemically treated timber”Timber treated with certain preservatives can be corrosive to galvanised steel in damp contact.
How to avoid it
Section titled “How to avoid it”- Use matching or compatible material pairs.
- Separate them: insulating washer, coating or membrane where the pairing is unavoidable.
- Keep it dry: no moisture, no process.
- Design the drainage: do not let runoff from a foreign metal reach the structure.
The point
Section titled “The point”Corrosion does not always start from the steel but from what touches it. Material pairing is therefore a detailing decision, not a procurement one.