Moss, lichen and algae settle on stone slates more easily than on almost any other covering, because the stone is rough and absorbs water. Taking them off is where stone roofs get damaged. A slate that looks sound can be cracked underneath, a peg (the wooden pin that hangs a stone slate from its batten) can be loose in its hole, and a well-meant jet of water can drive into the laps, the overlaps between courses, and loosen what it was meant to clean.
This guide covers cleaning for stone and natural slate: what hand methods involve, how we move across a roof without breaking it, what to keep away from the surface and what changes for a protected house. For the damage moss itself can do to a covering, read can moss lift roof tiles. For the overview of the service, go to roof cleaning and moss removal.
What a mossy stone roof is carrying
Start with the weight. Cotswold District Council's 2000 technical guidance gives about 1,000 kg for every 10 m² of stone slate roof, and the timbers beneath were sized for that and little more. A roof soaked with moss, which holds water like a sponge, carries still more, and a person walking on it adds a point load at exactly the wrong place.
Then there is the way the slates are held. Traditionally each stone slate hangs over a batten, a timber strip nailed across the rafters, by a peg of cleft oak, or sometimes two, pushed through a drilled hole close to its head. Nothing clamps the slate down. Gravity, the pegs and the courses stacked above hold it down. That is a gentle system when it is left alone, and a fragile one when someone scrubs at it.
Why the roof is more delicate than it looks
The same guidance records that stripping a stone roof commonly shows about 50% of the slates perished. Perished means the stone has delaminated, split into layers or crumbled along its beds. Many of those slates are still sitting in place on the roof looking whole, held by their neighbours. Moss often masks them. So the first rule of cleaning a stone roof is to assume that some of what you are standing next to is weaker than it appears.
Hand scraping stone slates with the lie of the roof
Hand scraping is the standard method on stone, and it is the one we start with. On the slope we use a flat scraper and a stiff-bristled brush, lifting the moss from the faces of the slates and out of the joints between them.
Direction of work
The courses overlap like fish scales, each tail lapping the head of the course below. We scrape downwards, in the direction the water runs, so that the blade never catches under the lower edge of a slate and lifts it. Working upwards is how a slate gets pushed off its peg.
Tools that suit the stone
A blade with a rounded, blunt edge removes growth without scoring the face. A sharp, hard blade used on soft limestone leaves scratches that hold water and give moss a better grip next time. A stiff brush follows the scraper to take off what is left, and we stop short of anything that would strip the weathered surface, because that surface is the roof's own protection.
Catching what comes off
Moss is raked down onto boards or sheeting and bagged, and not pushed into the gutter. Stone roofs often drain to cast-iron or half-round gutters that have no spare capacity, and a lump of wet moss in a downpipe is a nuisance that could have been avoided.
Frequency beats force
Cotswold District Council's guidance ties a yearly scrape to a stone roof lasting up to twice as long. We would promise that for no roof, but the point stands: light, regular attention is kinder than a rare heavy clean on thick growth. MyBuilder's 2026 guide puts hand scraping at about £5 to £10 per m², against £15 to £20 for soft wash, so it is also the cheaper method per square metre, though it takes longer.
Pegs, peg holes and the slate that breaks underfoot
Most damage on a stone roof comes from how people move, and not from the cleaning tool. A slate is strong in compression but weak across its width, and it breaks when a load falls between two battens.
Spreading the weight
We do not walk on the face of stone slates if there is another way. A roof ladder that hangs from the ridge, the top line where the slopes meet, takes the load and puts it onto the battens through the ladder's own rails. Where a roof is high or steep, scaffold, a tower or a platform at the eaves is safer for the person and gentler on the roof. Scaffold is its own item in the quote, which shows you its share of the cost.
Testing before trusting
Before weight goes onto a slope, we look at how the slates are sitting. Slipped slates show as a tail line that dips, a visible gap or a darker stain beneath the lap. A hairline crack across a slate can look like a change in colour. If a slate rings dull when tapped lightly with a knuckle, it is likely to be split. Where we find one, we note it, and we do not scrape over it.
Loose pegs
An oak peg that has rotted or split lets its slate slide down the batten by a centimetre or two, and the slate then sits lower in the course than its neighbours. We photograph these. Refitting a peg is a repair, not a cleaning job, and we agree it with you so that you can decide. Our page on the Cotswold stone roofing service covers re-pegging and re-laying.
A broken slate found during a clean is better known about than not. We list every slipped, split or loose slate we see in the written report and in the photographs, so nothing is a surprise later.
Natural slate: a harder face with its own weak points
Natural slate is denser and smoother than limestone, and it stands up better to scraping. It is not without risk, and the risks are different.
Nails, not pegs
Slate is normally fixed with nails, sometimes with hooks or clips, through holes near the head or the side of each piece. Over many years a nail can corrode or work loose, and the slate then hangs by a thread of fixing. A hard push upwards with a scraper can free it. We keep to the downward stroke on slate as on stone.
Delamination
Slate splits into thin leaves along its natural layers. Once the outer leaf has started to lift, it breaks off in flakes under a tool, and the face below is rougher and holds moisture. Brushing lightly is safer than scraping hard on a slate that is already flaking.
Scoring and polish
A hard blade scratches the face, and the scratch shows for years. Careful handwork does not mark the slate. This matters on a roof that is seen from the lane.
Cost context
MyBuilder's 2026 guide puts the cost of a slate roof clean at about £500 to £1,000, and a tile roof at £400 to £750. Those are national figures for comparison. A steep or shaded slate roof sits towards the upper end because of the time and the access, and once we have surveyed, a written quote in writing shows the method chosen for each slope.
What to keep away from stone: jets, harsh chemicals and fast fixes
Some of the methods used on modern tiles do not suit stone, and it is worth knowing which, because a contractor may offer them without saying so.
High-pressure water
MyBuilder's cost guide cautions about jets on delicate tiles, and a stone roof is more delicate than most. A jet can strip the weathered face off limestone, drive water up under the laps and wash out the bedding along a gable edge. It can also push an already loose slate off its peg. We do not pressure wash stone slates, and the reasons are the weight of the water and the way stone drinks it up.
Strong cleaners
Limestone reacts to acids, and strong or unsuitable products can etch the surface. Where a treatment is considered, it is a low-pressure biocide chosen to suit the stone, tested on a small patch first and applied from a safe position. The product label is followed for dilution and for what it is safe near. On many stone roofs the better choice is to scrape and leave the surface alone.
Sealing the surface
A coating or sealer sold as a way to keep growth off can hold moisture inside a porous stone. We would not apply one to stone slates, and our guide on roof coatings after cleaning explains why.
Frost in the stone
Stone that is wet when frost arrives can flake at the surface. That is one more reason to clean in a dry spell and not to leave stone soaked by a heavy-handed method.
Conservation sensitivity: patina, lichen and listed houses
Much of the Cotswold stone in this area belongs to protected buildings or sits within a conservation area. Stroud District has 41 conservation areas, and the Cotswolds National Landscape covers just over half of it. Both shape how a clean is done, even where no formal consent applies.
Listed buildings
The council's own listed building guidance treats every grade alike: the entire building is protected, inside and out. Cleaning by hand to remove moss is ordinary maintenance, but anything that alters the appearance of the roof is a different matter: stripping off weathered stone, applying a coating, replacing slates with a different stone. On a listed house, speak to the conservation team before work that goes beyond hand cleaning.
Conservation areas and Article 4 Directions
Five Stroud conservation areas carry Article 4 Directions. The council's page is silent on roofs, so ask its planning team first.
Patina and lichen
The grey, yellow and orange crusts that settle on old stone are part of how a roof looks, and conservation officers often prefer them to be left unless they are doing harm. We would not strip a roof back to bare stone on a protected house, and we talk through the choice with you using photographs. Our guide to lichen on roof tiles sets out when lichen is left in place and when it is removed.
Replacement slates
If cleaning shows that slates must be replaced, replacement stone, under the English Heritage policy in that 2000 guidance, should agree with the original in type of rock, colour, grain, size and thickness. Like stays with like.
What a stone roof clean looks like on the day
Before anyone goes up, we survey the roof from the ground and, where access allows, from the eaves. We look at the covering, the pitch, the amount of growth, the state of the gutters and where trees drop debris. The survey gives you pictures of your own slopes, followed by a written quote covering access, each slope's method, gutters and waste.
The sequence
Access goes in first, whether that is a roof ladder, a tower or scaffold. Boards or sheeting go down below the eaves to catch debris. We scrape and brush, working down each slope. Moss is bagged and taken away. Gutters and downpipes are emptied and flushed through. Any slipped, split or cracked slates are photographed, and you are told what needs a separate repair visit.
What you receive afterwards
Before-and-after photographs, a note on the shaded slopes that are likely to grow back first and, if the roof calls for it, advice on when to look again. Nothing is left on site, and the 10-year workmanship guarantee comes in writing.
A call to 01453 933613, or a few photographs sent on WhatsApp or the contact form, is enough to start. The pictures often show whether hand scraping will do.