Black Stone Issues – Series One: How to restore colour to black stone

A newly installed black stone patio is an impressive sight – but its wow-factor often doesn’t last long.  Black or very 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 that a newly installed patio retains its good looks?  LTP provides the solution, with its Blackstone Sealer & Restorer.

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 discolouration, 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 – and restore an existing patio

Good quality water-resistant sealers go a long way in reducing discolouration – 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.

LTP Blackstone Sealer & Restorer provides a long-term solution, by protecting the surface and creating a permanent colour enhancement.  The treatment is a water-based, impregnating sealer which 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 around 4-5 year. 

Choosing a water-based treatment, like Blackstone Sealer & Restorer, 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 that no rain is forecast for 24 hours, either side of application. 

How to apply LTP Blackstone Sealer & Restorer

Stage I – Preparation:

Ensure that the surface to be treated is completely clean, dry and free from dirt, grime, cement, and grout. If necessary, wash the surface first with a dilute solution of LTP Grimex 1:5 and scrub with a white nylon pad. Rinse well to remove residues and leave to dry.

For older surfaces, remove blackspot, algae, mildew and stains from detritus with LTP Blackspot & Algae Remover. Apply undiluted and leave for up five hours. Rinse and leave to dry.

Stage 2 – Treatment:

Wear gloves and ensure that any surfaces not to be treated are covered and protected. 

IMPORTANT: Blackstone is a permanent staining solution that will darken the surface of the stone and the grout joints; it will be very difficult to remove once applied. Blackstone is an impregnating sealer that needs to fully absorb into the stone. It is not film forming, so any excess left on the surface should be removed. Always test on a small area before general application, to help establish best method and optimum number of coats required. Do not walk on treated surfaces until the solution has completely dried. NB. Do not use when surfaces are very cold or very hot. Ideally between 5 – 25°C.

Shake the bottle well before use. 

Work in small, manageable areas, i.e, as far as you can reach without stepping into the solution. Apply a small amount to the surface and spread out evenly using a sealant applicator, foam roller or paint brush.

Allow the solution to penetrate the stone. If a second coat is required, apply immediately after the first has absorbed. Do not allow the first coat to fully dry before application.

NB. Do not walk on the surface for at least four hours after the final application. Once dry, and to help ensure an even application, it may be necessary to work off any visible excess using a dry towel.

Allow newly treated surfaces 24 hours to cure. If necessary, wash surfaces with a 1:10 dilute solution of LTP Powerstripper. This will help to remove any excess that is difficult to rub off. Before allowing traffic, gently rub the surface in a few areas with white cloth or paper towel to make sure that it is colourfast.


The Blackstone product page includes additional information, including a video aid and coverage calculator.

For more information and expert advice on surface protection and maintenance, please contact LTP on tel. 01823 666213 or email info@ltp-online.co.uk

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