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What causes black spot and how to remove it .

Mark Atkins of LTP explains how to address this insidious microspore’s effects on tiling installations

Regular patio maintenance brings lots of benefits. It retains a tile’s aesthetic, along with its performance, and reduces the need for intensive cleaning and re-sealing down the line.

Most organic stains are relatively easy to remove, especially if the surface has been sealed, but there are some that can prove more difficult, like black spot.

Despite its name, black spot can be black or white and it originates from plants and trees. This dust-like lichen microspore is carried by the wind and rain and it colonises on stonework, taking about 2-3 years to get really established below the surface. Black spot thrives in damp, shady places, sending its tendrils or “hyphae” down into the stone’s pores, searching for nutrients. It’s a particular menace in porous stone, as the open texture enables microspores to spread more easily, but even less porous materials like porcelain aren’t immune. Here, the lichen can still create a slippery residue on the tile surface.

Why water doesn’t work
A pressure washer and a dose of household cleaner is a common go-to treatment. However, this doesn’t work because hyphae become anchored into place below the surface. In fact, the extra dose of water only makes conditions even better for the rampant lichen. Also, pressure washing can damage the surface of the stone, loosen the grout and, if any protective sealer is applied, it will damage that too.

A specialist, two-pronged attack is necessary in order to remove black spot stains and the microspores below the surface. Any treatment needs to have a bleaching action, to restore the colour of the tile or paver. It also needs to target the hyphae below the surface. Care needs to be taken though. If a treatment is acidic, it can damage acid sensitive material and erode the grout joint.

Removing stains and preventing regrowth
LTP’s Black Spot & Algae Remover targets organic residue, and is designed to restore appearance to natural stone, concrete, brick and porcelain. Developed to deep clean paths, patios and driveways, the treatment targets black spot, lichen, moss, algae and other stains caused by damp and slippery leaf matter.

Three case study examples, shared by Alastair Niddrie from stone maintenance specialist – Silex UK – illustrate treatment with this product at sites throughout the UK: The first, a York Stone and brick installation in Chiswick, had a build-up of green algae and black spot over 30 years. As well as white and black staining, the lichen was creating a slip hazard. At the second site in Dorset, a large limestone patio was stained with black spot, algae and dirt. The client was considering replacing the patio as repeated jet washing hadn’t resolved the issues and had damaged some areas of paving. The third site – a courtyard in London – was also deeply stained with black spot and algae.

Niddrie says: “These types of stains are notoriously difficult to remove and a blast with a jet wash just makes matters worse. We’ve found a solution with LTP Black Spot & Algae Remover. It’s formulated to cling to the surface and once absorbed, it breaks down the hyphae within the stone porosity, as well as the slippery residue on the tile surface. A bleaching action also removes the staining, to restore surfaces to their former glory. We’re delighted with the results and now routinely use the treatment on all patio refurbishments”.

Before application, surfaces should be swept clean. The product is then applied using a watering can or light pressure garden spray, where it fizzes during treatment. It should be left to act for 2-4 hours and surfaces are then hosed with clean water. The solution can be used on dry and slightly damp surfaces and should be applied during a morning or afternoon of fair weather.
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