Rust Marks on Paving
Rust may become a problem with paved areas for a number of different reasons. Concrete
slabs, constructed using sand and aggregates that contain even minor traces of iron ore in the
base material can cause serious outbreaks of rust staining, especially those that are produced
under less-than-ideal conditions. These marks manifest themselves as brown stains, ranging
from light brown to almost black, where the iron ore is at surface level within the slab. In
these cases, it is best to lift and replace the offending unit, as the problem is deep seated.
Rust stains caused by metal furniture or other ferrous metal (especially problematic – gas
cylinders used for barbecues) can leave unsightly markings, which will expand if left too
long unattended. Common household cleaners should be avoided, as they may worsen the
problem. Vinegar and other mild acid should also be avoided for the same reason.
Other causes of rust staining are fertilisers containing iron sulphates – especially those used
as moss killers – which may drift onto paved areas during lawn operations. These should be
swept off as soon as possible, although if the paving is damp, the damage will have been done.
There are suitable proprietary brands of non-acidic rust cleaners available from builder’s
merchants, and it may be beneficial to have some to hand in the garden shed (or
landscaper’s van).
Rust can also be caused by the use of acids, used to clean down cement stains from landscaping
operations, as the acid will draw any ironstone content within the slab – primarily sandstones
– upwards through the slab to manifest as brown patchy stains on the surface of the slab.
Although these may fade after months of rainfall and wear, it is best to avoid any type of acid
when cleaning natural stone. (See Acid Use on Paving.)
