A NEWLY installed black stone patio is an impressive sight – but its wow-factor often doesn’t last long, says Mark Atkins, technical director at LTP.
Black or dark grey stone very quickly fades and you’re left with a wishy-washy grey aesthetic. So, how can you restore the colour and protect slabs from future discolouration, or ensure a newly installed patio retains its good looks?
Why does black stone fade?
A dark stone’s appearance can be greatly affected by UV light and normal rainfall because it causes a chemical reaction. Limestone and many other dark stones are calcium-based, alkaline in nature and sensitive to acid. They contain a soluble mineral called pyrite; when this is combined with water and oxygen, it forms sulphuric acid, which dissolves the calcium and changes the colour of the stone.
Meanwhile, as rain falls, it absorbs carbon dioxide from the air, which dissolves to form carbonic acid. This makes it slightly acidic – around 5.6 on the pH scale, rather than a neutral value of pH 7.
Rainwater, humidity, and UV-rays all contribute to discoloration, as does erosion caused by the wind and general wear and tear. Acidic maintenance chemicals can also cause additional damage, as can jet washing.
How to protect new slabs or restore an existing patio
Good quality water-resistant sealers go a long way in reducing discoloration – and many can enhance colour too – but rainfall also damages the protection that they create. Topical sealers can be worn away and rainwater that seeps into the stone’s porosity will eventually compromise the effectiveness of an impregnator.
Says Mark: ‘Quality formulations that seal and restore, such as ECOPROTEC Blackstone Sealer & Restorer, provide a long-term solution by protecting the surface and creating a permanent colour enhancement. A water-based, impregnating sealer, Blackstone contains a permanent colour intensifying pigment. It can be used on limestone, marble, slate, and concrete pavers. To maintain a very dark, pristine finish, annual treatment is recommended, although a treated stone will maintain a far darker aesthetic than an untreated stone for about between four-to-five years. Choosing a water-based treatment such as Blackstone, provides safety and environmental benefits. It can also be applied in damp conditions, so application is much easier and can be carried out at any time of the year, provided no rain is forecast for 24 hours, either side of application.’
Why good preparation is key
If you’re looking to restore a faded limestone, it’s really important to ensure tiles are properly cleaned and prepared before any restoration is carried out. When a restorative treatment is applied to black stone, it mixes with any loose particles of limestone. These particles are caused by etching which occurs when the stone comes into contact with the acidic rain.
The etching creates a sediment which is carried into newly exposed capillaries and the sealer, in turn, draws the sediment out of open pores. When this residue mixes with the sealer, it creates a smeared and patchy appearance.
Says Mark: ‘A thorough clean with ECOPROTEC Stone & Tile Intensive Cleaner will remove the sediment and condition the stone, before application of Blackstone. If you rub your hand across the surface before cleaning, you’ll see a dusty residue; that’s the limestone sediment. Cleaning the surface opens the pores and prepares the stone for application of the sealer.’
Less is more
Don’t be tempted to over-apply your restorative treatment in order to achieve a darker finish or speed the process up. It’s far better to apply several thin layers than one thick layer. If you apply too much product in one go it won’t be absorbed properly and the finish will be patchy.
Continues Mark: ‘Residue treatment should be removed with ECOPROTEC Stone & Tile Intensive Cleaner, using a 1:10 dilution. This is an important part of the process because the treatment only works in the pores of the stone, where the formulation cross links to make the sealer colourfast.
This final clean won’t return the stone to its original colour, it’ll just remove excess treatment that hasn’t been absorbed and is effectively just sitting on the surface.’
For more advice on stone and tile protection, maintenance, and refurbishment, use the below contact details.
01823 666213
technical@ecoprotec.co.uk
www.ecoprotec.co.uk
