Rust marks on interlock come from three places: metal furniture and railing feet, iron in fertiliser spread across the surface, and well water used for irrigation. All three leave the same orange stain, and all three need an acid-based product formulated for rust rather than anything that works on dirt.
Rust is iron oxide that has bonded chemically with the surface of the paver, which is why mechanical cleaning and organic cleaners do nothing to it. The products that work are acidic, usually oxalic or a proprietary blend, and they dissolve the oxide so it can be rinsed away.
That works, and it is also why this is not a good candidate for a confident weekend attempt: too strong or left too long and the acid attacks the cement paste holding the paver together, leaving a permanently rough lighter patch exactly where the stain was. On coloured pavers it can also pull pigment.
We test somewhere hidden, apply at the lowest effective strength, and neutralise afterwards so nothing is left working. The other half of the job is finding the source, because a railing post or a fertiliser spreader will keep producing the stain otherwise.
A railing foot, a fertiliser spread or irrigation water. Without dealing with it the stain returns regardless of how well it comes off.
Test somewhere hidden
Acid on coloured pavers can pull pigment as well as rust, so a patch out of sight shows how your surface reacts before the visible area.
Apply at the lowest strength
Start weak and work up. Too strong attacks the cement paste and leaves a rough lighter patch exactly where the stain used to be.
Neutralise and rinse
The product is stopped rather than left, since an acid still active after the job is finished is how a treatment turns into damage.
Fertiliser Season
Most rust marks arrive in spring
Iron-rich lawn fertiliser spread with a broadcast spreader throws granules several feet, and the ones that land on paving dissolve in the next rain and stain it. It is the most common source we see and the easiest to prevent: sweep the hard surfaces before it rains rather than after.
Usually iron in lawn fertiliser that landed on the hard surface, or a metal railing foot or furniture leg. Well water used for irrigation is the third source.
No. It lightens the paver around the stain and leaves the rust, so you end up with an orange mark on a patch that is now a different colour to everything else.
At the right strength and neutralised afterwards, yes. Too strong or left too long it attacks the cement paste and on coloured pavers it can pull pigment.
You can buy the products, and the failure mode is a permanent rough light patch where the stain was. That is why we test out of sight first.
Deal with the source. Sweep hard surfaces after spreading fertiliser, put pads under metal furniture feet, and check railing posts for rust running down.
It can be, if the water carries iron, and the giveaway is a stain that follows the spray pattern rather than running from one point. The other common source is fertiliser with iron in it landing on the paving. Both come back every season until the source moves.
