Safely and effectively removing unwanted soiling, staining and coatings from historic buildings

By Jamie Fairchild, Building Conservation Masterclass Tutor

Graffiti removal is an important aspect of Masonry Cleaning especially when it relates to a delicate historic surface such as this example; plasterwork within a C12th monastic ruin, part of the Scheduled Ancient Monument. Add some bats in the vaults beneath and a running flood in the adjacent river – how should we tackle this and safeguard the fabric and ecology?

First carry out a site survey and meet the resident ecologist. Undertake some small spot tests and keep a photographic and written record. Propose a methodology for approval by the conservation body. Return ASAP to carry out the work. The ground beneath the masonry is unpaved – there is a high risk of the waste leaching into the soil or washing out to the river. To control this, we elect to use a Vacuum Recovery System. The hot rinse water sprays the surface within a hand held enclosure, connected to a vacuum. The waste water, paint and spent reagent is recovered and pumped to a tank in the vehicle.

We have a four step process to follow. Sometimes it’s successful after step 2, other times after step 3 or 4.

1. Pre-wash with superheated water – removes some graffiti and pre-warms the surface in low ambient temperatures.

2. Apply proprietary Graffiti Remover Gel. Dwell time up to 1.5 hours with occasional paint brush agitation. This mobilises the binder and the majority of pigment. Rinse with superheated water.

3. Ghost Remover (hypochlorite). Apply to the wetted surface, dwell time 10 mins. Gently agitate with paint brush. Rinse with superheated water.

4. After-wash (acetic acid – ‘white vinegar’). Application/removal as ‘3’.

We prioritise the most benign chemical reagents, at the weakest concentration and the shortest dwell. The acetic proved more effective than hypochlorite in this example, so we were able avoid the least desirable reagent. The obvious, most unsightly graffiti is removed, but once the bats are out of hibernation, we can come back and deal with the graffiti in the vaults.

CPD - Brick and Flint Masonry

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