Iron breakout is a common cause of orange staining on patios and paths, and the resulting marks can be difficult to remove. They’re frequently mistaken for stains caused by rusting or flaking metal objects, such as BBQs, metal umbrella stands and garden furniture. As a result, the affected area is often treated with a standard brick and patio paving cleaner, typically containing acid.
But this is where problems arise. These cleaners won’t remove naturally-occurring rust stains and can actually accelerate orange discolouration in some natural stones. The cause – and therefore the appropriate treatment – is very different.
What causes naturally-occurring rust stains?
Rust or orange-coloured discolouration can appear naturally within iron-rich natural stone pavers – and it’s especially common in sandstone. These stones naturally contain iron which can oxidise or rust when it comes into contact with water and oxygen.
Staining often appears after laying and is easy to identify. Rather than forming a defined mark, the colour gradually develops across the surface, creating a widespread orange or brown bloom.
What causes rust spots and rust stains?
In contrast, surface rust stains from objects often mirror the exact shape and position of the rusting metal that was sitting on the surface. Some weed killers and lawn fertilisers can also create rust stains; this is caused by iron compounds, like ferric sulphate, and these stains typically appear as small spots of rust.
Once you’ve established which type of rust stain you’re dealing with, removal can be swift and effective, provided that you use the correct product.
A case in point
We were recently contacted by a customer regarding widespread orange staining on natural grey sandstone. The pavers had a relatively smooth non-slip finish. A hydrochloric-acid based wash had been used to remove dirt and light staining. It was applied following the manufacturer’s instructions. A few days later, widespread orange/brown staining appeared across multiple slabs.
Our Rust Stain Remover was recommended by a local paving supplier. This remover is non-caustic and non-acidic and is particularly suited to natural stone. It is highly effective at removing surface rust stains, but it is not formulated to treat naturally-occurring iron oxidation within the stone.
Initially, the treated area looked much better but, after approximately one week, the orange staining gradually reappeared. The treatment was then repeated two weeks later. Once again, the pavers appeared significantly improved immediately after treatment. However, within a few weeks, some of the orange staining had returned.
Why the wrong treatment won’t work
Rust stain removers – even non-acidic solutions like our own LTP Rust Stain Remover – won’t remove naturally-occurring rust stains. In some cases, treating iron-rich stone with the wrong product can trigger or worsen discolouration by affecting iron compounds naturally present within the stone. This can result in ‘iron break-out’ – a reaction involving the iron within the stone that causes it to oxidise and produce the characteristic orange discolouration.
To treat this type of staining, you need to use LTP Ferrex Iron Stain Remover – a treatment specifically formulated for naturally-occurring iron staining.
How to apply LTP Ferrex Iron Stain Remover
Dampen the surface of the stone with a little water. Dilute the cleaner 1:1 with water and spray onto the surface. Leave to work for up to five hours. The orange staining should gradually fade and disappear. Once it has disappeared, seal the stone with LTP External Stone Sealer to help prevent the orange staining from returning.
So, what’s the difference between the treatments?
The chemistry used in our non-acidic Rust Stain Remover helps remove orange staining caused by rusting metal objects on the surface of the stone.
The chemistry used in Ferrex Iron Stain Remover treats the oxidation of naturally occurring iron within the stone, removing the resulting orange discolouration rather than removing the iron itself.
So, for rust on the stone, use LTP Rust Stain Remover and for iron in the stone, use LTP Ferrex Iron Stain Remover.
By Mark Atkins, LTP Director
