How to restore colour to black stone

A newly installed black limestone 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?  We recommend treatment with LTP Blackstone Sealer & Restorer.

Why does black stone fade?

A dark stone’s appearance can be greatly affected by sunlight 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’s 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, we recommend annual treatment, 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:

Before application, make sure that the slabs are as clean and dry as possible.  If necessary, clean with a dilute solution of LTP Grimex (diluted 1:10), rinse well and leave overnight to dry.  If you’re treating an older patio that’s stained with blackspot, algae and mildew, etc. carry out this initial wash with LTP Blackspot & Algae Remover instead. Apply to the surface undiluted and leave for up five hours. Rinse and leave to dry overnight.

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. Test on an inconspicuous area before general application and do not walk on treated surfaces until the solution has completely dried. 

Shake the bottle well before use. 

Honed and smooth surfaces: apply a small amount to the surface and spread out evenly using a soft cloth or sealant applicator. NB. To ensure even application it may be necessary to work off any excess sealer using a soft cloth; leave the surface to dry out for at least four hours before carrying this out. Apply any further coats at two hourly intervals until the desired depth of colour has been achieved. No more than three coats should be applied in total. Work off any excess sealer using a soft cloth and leave to dry naturally.

For rough cut or textured surfaces: apply a small amount to the surface and spread out evenly using a foam roller or paint brush. Allow to absorb and dry. Apply further coats at two hourly intervals until the desired depth of colour has been achieved. No more than three coats should be applied in total. Leave to dry naturally. 

Always allow newly treated surfaces to cure for 24 hours and then rinse with dilute LTP Power Stripper; this will help cut back any excess sealer. Before using the patio, gently rub the surface in a few areas with white cloth or paper towel to make sure that it is colourfast. 

Always experiment on a trial area first to establish optimum results. 

For advice on patio protection and maintenance – and to stock up on LTP treatments – pop in and see us or contact our showroom team on 01823 667242.

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