Graffiti on heritage masonry is one of the few jobs where the removal method matters more than the removal itself. Get it wrong and you trade a painted wall for a permanently damaged one, and the damage is usually more visible than the tag was.
Why the usual methods hurt old stone
Chemical strippers work by softening the paint so it can be washed off. On dense modern surfaces that is fine. On porous sandstone or soft lime mortar, the stripper and the dissolved paint travel into the stone rather than sitting on it. You remove the surface colour and drive the rest deeper, then the residue keeps working, and salts and staining come back out over the following months.
Abrasive blasting removes the paint by removing the surface. On heritage brick that means taking off the fire skin, the hard outer layer formed in the kiln, which is the part doing most of the weathering protection. Once it is gone the brick absorbs water and decays faster. The wall looks clean and is measurably worse off.
Both approaches are still used because they are quick and cheap. On a listed or significant building, both can also be the thing that turns a maintenance item into a conservation problem.
What a laser does differently
The paint absorbs the pulse energy and leaves. The masonry underneath, being a different colour and a different material, absorbs and conducts differently and takes far less. The process can be tuned so it removes the coating and stops close to the substrate, which is the whole reason conservation work uses it.
There is no water, no chemical, no abrasive and no spent media. On a public building that also means no wet slurry running down the footpath and no containment tent for a small tag.
It is slow compared to a pressure washer and it is not the cheap option. It is the option that leaves the fabric intact.
The ghosting problem
The thing to understand before anyone starts is that removal is not always the same as invisibility.
Where paint has soaked deep into porous stone, the laser takes what is at and near the surface. Pigment that has migrated millimetres into the stone is beyond the depth the process can reach without starting to remove stone. What you get is a very substantial improvement with a faint shadow remaining in some lights.
The same is true where a previous attempt has already been made. Chemical stripping before laser work usually pushes pigment deeper and makes a complete result less likely. If a tag has been attacked with a stripper first, say so, because it changes what we can promise.
Anyone promising a perfect result on deeply soaked porous stone without seeing it is guessing. The right approach is a test patch in a discreet area, so you see the actual outcome before committing to the whole elevation.
Different paints behave differently
Spray enamels and acrylics generally respond well. Some inks and dyes penetrate much further and are far harder. Metallic and silver paints reflect a good deal of the energy and are slower. Very thick, built up layers from repeated tagging take proportionally longer.
Substrate matters as much. Dense granite and hard fired brick tolerate the process well. Soft sandstone, lime render and heavily weathered stone need gentler parameters and more care, which means more time.
What a job actually involves
A test patch first, in a location the client agrees on, to establish parameters and set expectations. Then a controlled work zone, because this is a Class 4 laser process and that applies just as much on a footpath as it does in a workshop. Screening, correct eyewear, exclusion of the public, and fume extraction at the head.
On a public facade that usually means working out of hours or with traffic management, and that is often the larger part of the cost on a small area.
When we would tell you to use something else
Modern painted render or a coated surface that is due for repainting anyway. There is no point paying for careful conservation removal on something that is about to be covered.
Very large areas of light staining on hard fired modern brick, where gentler methods will do without harm.
Any situation where the wall is failing for other reasons and the graffiti is the least of the problem.
Our laser cleaning page covers the wider range of surfaces we work on, and the same principles apply to soot, lime scale and biological growth on heritage stone.
Talk it through
We do this work for industrial asset owners and their facility managers, infrastructure owners, principal contractors, asset managers and heritage architects, to the engineer's or heritage architect's specification. We do not take on homeowner, house, cottage, fireplace, strata, balcony, apartment or single dwelling work, or small domestic jobs.
Our laser cleaning, rust and paint removal page covers where we work and what we run. Ring 02 7912 3054 and we will tell you which tool suits your job. We run both, so we have no reason to push you at the wrong one.
Perfect Remediation acknowledges the Aboriginal and Torres Strait Islander people as Traditional Custodians of the country on which we live and work. We pay our respects to the Traditional Custodians and Elders past, present and future, and honour their connection to the land and ongoing contribution to society.