Green algae, moss and lichen make stone look neglected, but the bigger problem is the moisture they trap against the surface. This guide explains how to remove biological growth from stone safely, without the damage harsh methods cause.
Key takeaways
- Algae, moss and lichen hold moisture against stone, which can accelerate frost and salt damage.
- Pressure washing removes growth but soaks the stone and can erode soft surfaces and mortar.
- Biocides kill growth but need careful handling and can leave residues.
- Laser cleaning removes biological growth dry, without soaking or abrading the stone.
Why biological growth is a problem
Biological growth is a problem because algae, moss and lichen hold moisture against the stone surface, and persistent damp accelerates frost damage, salt movement and surface breakdown. It is not only an appearance issue.
Damp, shaded and north-facing surfaces are the most affected. Over time, roots and rhizines can work into the surface and open it up to further weathering.
The trouble with pressure washing
Pressure washing removes growth quickly but soaks the stone, can erode soft surfaces and mortar, and often leaves spores behind so the growth soon returns. It treats the symptom and adds moisture, the very thing that feeds the problem.
On heritage and soft stone the erosion risk is serious, which is the same concern we raise in cleaning sandstone without damage.
Biocides and their limits
Biocides kill biological growth so it can be brushed off, but they need careful handling, take time to work, and can leave residues or affect surrounding planting. They are a chemical treatment with the usual handling and disposal considerations.
They can be useful as part of a managed approach, but on their own they do not give an immediate clean result and they introduce chemicals to the surface.
Need this done by professionals?
LaserStrip provides mobile laser cleaning across the UK. Heritage approved, chemical free, fully insured. Tell us about your project for a fast quote.
How laser cleaning removes growth
Laser cleaning removes algae, moss and lichen dry, by vaporising the growth with light, so the stone is not soaked or abraded and there is no chemical residue. It clears the surface while protecting it.
Because it does not add moisture, it avoids feeding the very problem that other methods worsen. See our heritage stone cleaning service, or send photos for advice.
