Common products you shouldn’t use to clean patios – ‘damage and ruin’ slabs

Express.co.uk spoke to Jonathan Kirby, Roxil’s decking and paving expert about the do’s and don’ts of removing black spots.

Jonathan said: “Whether your outside area is made up of natural stones, patio slabs or decking, it will inevitably show some form of biological growth over the winter and spring months, such as algae, mould and lichen.

“But these are nothing compared to when black spots appear. Not only do they make your outside area look a little tired and grubby, they are very difficult to properly remove, especially from patios, that haven’t been treated beforehand as they take root in the pores of the flagstones.”

What not to do

Put down the pressure washer

Jonathan explained: “While it’s tempting to blast away dirt, this won’t be able to completely remove black spot lichen from patios or decking. And frequent use can also cause long-term problems; blowing out pointing and dispersing jointing sand for patios, as well as damaging the fibres of the wooden boards and causing splintering in decking. This makes the rate of moisture ingress worse, which increases the likelihood of mould and algae.

“For wood, it also risks causing warping and rot – and this a death sentence for your decking if left untreated.”

Avoid bleach

He added: “Similar to pressure washing, using bleach or bleach-based cleaning products will damage the surface of your decking or patio.

“The bleach changes the cellular structure of the wood, which weakens the decking and changes its colour. It can also break down some finishes and coatings, which then leave the decking susceptible to water and other chemical damage.

“For patios, it can discolour or ruin the finish of your stones or pavers. And of course, if you have flower beds, a lawn, or plants, run-off could also be harmful to your garden – even when diluted.”

Wrong chemicals, wrong place

He continued: “Applying the wrong chemicals can harm your patio and (arguably more importantly) the environment that surrounds it.

“For instance, a salt solution might get some staining off as it’ll act as an abrasive, but it can damage your lawn. Also, washing up liquid might lift some very light staining, but it’s not going to kill algae or lichen and could kill plants in surrounding areas.”

Home remedies

Jonathan said: “Non-home remedy treatments (i.e store-bought products) come with instructions and an indication of hazards. But not only that, products for killing biological growth on patios must be cleared for use by the HSE.

“Home remedies touted on TikTok might look effective in the video, but it’s always safest – both for you, your garden and your patio – to know how to use the products you’re using correctly to avoid any unwanted consequences. “

How to remove black spots

Take time to prepare

He explained: “Before applying any cleaning products, the first step is to give your patio or decking a brush as this will help remove any loose debris before you start applying your cleaning products.

“Make sure to wear gloves to protect the skin on your hands and follow any instructions relating to the safe handling of the product to avoid risking any irritation as you apply the product.”

Check the weather forecast

The expert advised: “If you’re planning to use a product that needs to be left on for several hours (which is common for the best results), make sure to check the weather so it will have time to work its magic before rain washes it away.”

Don’t rush the job

Jonathan added: “Your patio or decking won’t be cleaned in 30 minutes, so make sure you give yourself enough time to do the job properly. Check the instructions of your chosen product to determine how long it needs to be applied.

“For the Roxil Wood & Patio Cleaner, for instance, we recommend leaving it up to 24 hours for the best results. Once the product has been applied according to the instructions, we’d recommend using a wet stiff brush to loosen any stubborn patches of mould, algae and dirt, before washing away the debris.”

Do use white wine vinegar

He added: “If you need a quick fix now, a simple 1:1 white vinegar and water solution works as a patio cleaner in a pinch. Mix as much as you need in a large bucket and pour the solution over the patio.

“Leave for around an hour to let the vinegar work, then scrub away the grime with a bristle brush and warm soapy water. Rinse thoroughly for a quick fix to clean your patio.”

Waterproof for less maintenance next year

He said: “Make your life easier next year and beyond by waterproofing your patio or decking. Algae and black spots all need moisture to grow, and it’s a simple step to maintain your patio in the long run.

“Check your patio or decking is entirely dry, then apply small amounts of a protective sealer directly onto the surface, such as the Roxil Wood and Patio Protection Creams.”