[Colin Stokes]

Sorry to ask but we concentrate on internal communal parts cleaning and external hard landscaping and have been asked to clean exterior galvanised steel air vents housed in concrete.

Any ideas - way out of my league but i presume if i use anything acidic then it will stain.

Client has no problem with cleaning it then sealing/hammerite (whatever) but i have no idea in how to clean it.

Any advice would be grateful or anyone in SW London that feels it would be worth a one off job to be a subbie.  Square feet wise its only about 60 feet in total.   

[BDCS]

Whats on them ?

[Colin Stokes]

I'm no expert but it looks like white deposits from water as it makes its way through.  I quite often seem similar deposits in stalactite form in car parks etc 

[BDCS]

Try something like selscale but I'm not sure about galvanised you would need to try a small area, I'd contact the manufacturers and ask them.

[Colin Stokes]

Wouldn't acid based cleaner stain the steel black?

[BDCS]

I'd try a small area and limit the dwell time to a minimum - If that dos'nt work then I'd contact your usual supplier and ask their advice - it is an unusual one and theres not a rush of answers.