In this regular column, Consultant Barry Hunt answers reader enquiries. If you have a question, email it to: nss@qmj.co.uk marked for Barry’s attention.
Q: Is there something I can treat stone patios with to stop leaf litter from staining them?
Stone is typically chosen for its aesthetic qualities while nature will do her utmost to upset these aesthetics. Leaf litter is one of the many issues in this ongoing battle.
Trees and stone patios do not really mix. Trees might release resins and fruits, gorging birds deposit some interesting compounds and colonising insects release all manner of chemicals. Light coloured stone can become blackened in a very short space of time under this onslaught.
Over time, the condition stabilises and the stone takes on an albeit discoloured patina, which I think is rather pleasing.
The stability is achieved in a number of ways. Pedestrian trafficking removes a lot of the surface dirt while the weather mellows things and bacteria and other microscopic organisms feast on the nutrients that are inevitably present.
There is no treatment I’m aware of that can specifically tackle patio staining, so the temptation might be to apply a sealer to try to stop the leaf litter and other tree products penetrating the stone, leaving it easier to clean. But that can lead to other problems, notably surface delamination. The sealing of external stones is a discussion for another day but generally such a course of action cannot be recommended lightly.
If you want to minimise the discoloration of your patio, the best course of action is preventative maintenance. You should trim and prune trees, though this may not have a significant effect. During autumn, leaf litter should be removed at least weekly and the patio hosed down to remove the tea-like film that develops. Bird droppings and other residues should similarly be frequently washed off. Jet washing may be appropriate to remove some of the stickier materials, but use a stiff plastic bristle brush if you have joints filled with loose aggregate.
Hopefully there are sufficient falls to help shed water, which will prevent some of the build-up, and drains should be kept clear. If mortared joints have failed, make sure they are repaired as water will run down them and saturate the bedding, leaving the stone damp for prolonged periods. The water that collects may also be loaded with organic matter that can return to the surface by capillary action as the stone dries.
There is often alarm when something new is stained, especially as such changes are at their most dramatic initially. Patience, a modicum of care, and a little understanding are all that are required for most patios to reach their potential.
Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646
Email: info@ibis4u.co.uk