Case Study:How Our Stone Cleaning Services Removed the Toughest Carbon and Lead Staining

As part of an ongoing restoration project, two facades of a Central London waterfront property situated next to Tower Bridge required advanced stone cleaning services. The ten storeys of this prestigious residential building had intense carbon and lead staining that required several specialist cleaning products and advanced methods.

Discover how the Spectrum stone cleaning team returned this affluent building to its original aesthetic condition in just seven days via a hybrid access method that included a DOFF pole steam cleaning system and expert abseiling.

The Logistics  

Spectrum was contacted by an existing client and property management company, First Port, with a confident referral due to previous stone cleaning services completed at the Royal Earlswood estate.

Knowing our experience and reputation with stone cleaning, the property manager trusted us to fulfil this prestigious, high-pressure project. We are also completing numerous other works for this property, including full restorative works on the metal and timber balconies, repainting of other metal features like window frames and railings, and gutter and window cleaning for the entire property.

As with all our services, the first step is to conduct an accurate pre-site assessment of the property to devise the most convenient, fast, and cost-effective plan for the services required. We identified the following features and challenges:

• The two facades of the property required hybrid access, using rope access and our pole system.
• The stone staining needed DOFF steam cleaning and specialist chemical treatment.  
• The stone edging that required cleaning was around the perimeters of all four elevations, mid-way up the property, at the top and across the balconies.

We also mapped out the access methods for ground-level stone cleaning and rope access and where the resulting exclusion zones were to protect the public.

The Project

The team arrived at Providence Square and established a safe system of work for rope access and the ground-level pole application. Confirming these locations appropriately enabled us to see where rope access was necessary.

Cleaning the stone at the rear of the building required rope access as it is waterfront to the river Thames. When working on the lower aspects of the facade, our team abseiled in correlation with the tides to ensure their safety. Having abseiling capabilities enabled our stone cleaning specialists to cover every inch of the substrate with accurate proximity without the need for expensive MEWPS or boats.

The staining on the property was a challenging mixture of carbon, biological and metallic. Lead flashing installed on the top of the stones had caused severe staining to the stone below, which proved difficult to remove and required trailing several specialist products.

Lead corrosion like this is caused by years of acid rain. We formulated a plan to counter this stubborn staining with DOFF steam cleaning services before using chemicals across the more deeply stained areas.

At Spectrum, we always consider our cleaning services' environmental impacts to remain as environmentally friendly as possible. While the DOFF cleaning at high temperatures and low pressure worked across the organic staining, the carbon and lead stains required further targeted treatment using chemicals.

The chemical paste we used contains ammonium in varying concentrates. After leaving it for 96 hours before removing and applying another steam clean, this process helps lift out the stone staining. Sometimes the staining requires we repeat this process two to three times before being satisfied with the result.

The Site

Providence Square is a prestigious residential property situated close to Tower Bridge in Central London. The property is distinguished by two large facades facing the waterfront and overlooking a Japanese-style water garden. The residential building is ten storeys high and has many luxury apartments.

The rear of the building is above the Thames and required rope access to clean the stone in time with the tides, avoiding high tides.

Challenges  

Two main challenges confronted us on this project. Firstly, the extent of the staining on the stone substrate. Particularly the carbon and lead staining.

And secondly, rope access at the rear of the building, with cleaning conducted in time with the low tides.

We easily removed the organic staining from the building with high-temperature and low-pressure steaming capabilities via our DOFF system. However, the non-organic staining required a specialist chemical treatment.

While the chemical paste and steam cleaning took a couple of attempts in some places, we swiftly cleaned the carbon and lead flashing stains to a fantastic standard for our client.  

Ground-level access for the front of the property meant we could clean this area using our DOFF pole system. But the rear of the building posed a different and more challenging situation.

Not only was rope access required to clean above the river, but the team had to time their stone cleaning with the low tides. By stone cleaning during high tides, we ran the risk of potentially needing a rescue boat as a safety precaution in case there was an issue.

Thanks to thorough planning during our pre-site assessment, we timed the abseiling team to precision, setting up a “rig for rescue” process during the low tides in case any technician became in danger of the high tides. This way, we could provide assistance to any team member in the event of stress, all from the rope system.

The Result 

Seven days of stone cleaning via rope access and a DOFF steam pole system have produced clean stone and refreshed brickwork. So satisfied with our work, our client has also asked us to complete further balcony decoration, restoration and timber repairs.

Here is a quick overview of our stone cleaning process that transformed Providence Square back to its original condition:

• The pre-site visit determined our stone cleaning strategy for the project. We confirmed the locations appropriate for ground-level cleaning and rope access.
• We established exclusion zones to protect the public.
• Our pole DOFF system began at the top left of each façade, working down each building from left to right.
• We repeated the DOFF cleaning system where necessary with steam cleaning, low pressure and high heat.
• Finally, we applied targeted treatments to the stubborn staining areas, such as lead corrosion and carbon staining.

Due to our rope access capabilities, we avoided the need for scaffolding of machine hire and made a significant financial saving to our client. Both parties were delighted with the result, with additional maintenance services scheduled for the future. 

So, if you require stone cleaning services for your London property, contact Spectrum today and receive a free quote.