Outdoor cleaning: moss, algae and dirty driveways
How to get moss off tarmac without wrecking the surface, a driveway brought back with a pressure wash and resand, and algae off a wall, done safely.
And for the lawn beside it
Power Packs: the 2.5kg bags cover 70 to 100m². The 8kg bags cover 228 to 320m².
Not sure of your size? Measure your lawnHow to get algae off a wall safely
Step by step, everything you need to clear algae off a wall or a fence, and how to do it safely. Jason gives me a hand on this one.
- The safety kit you need
- Why I don't use a knapsack for walls
- The three types of algae
- Why the wall looks worse first
- Working from the bottom up
- Brushed against unbrushed
What happens in this one
You need nitrile gloves, a spray suit with a face shield, a battery sprayer and a brush. Jason shows why a normal knapsack's no good for this. You have to stand right up close to the wall, and his face shield ends up soaked. With the battery sprayer you can stand back.
There are three types of algae. Green is the easiest to shift, red is harder, and black is the hardest. As soon as you start spraying, the wall looks worse, because the algae starts to run.
An algaecide isn't like a weed killer. It's a drench product, so you need a lot of water and product on the wall. Always start at the bottom and work up. The wet wall below helps the spray stick, so you get less runoff and use less product.
We sprayed the whole wall but only brushed one side, then came back to see if the brush was worth it.
The secret to a moss-free tarmac driveway
This one's not lawn care. It covers what keeps moss off a tarmac drive, with two bonus tips for cleaning other surfaces without a power washer.
- The maintenance that makes the biggest difference
- Why power washing tarmac backfires
- What soft washing is
- Why bleach and tarmac don't mix
- Why moss needs drenching
- Working from the bottom up
What happens in this one
Basic maintenance has the biggest effect on how much moss you get. Cut back trees to let the light in, and keep the leaves off through autumn and winter, when the sun's low and the moss moves in.
Tarmac is full of tiny dips, and that's where the moss grabs on. Power wash it and you wear the surface away a bit more each time, which makes more of those dips. Over time the moss gets worse and so does the driveway.
The better way is to soft wash it with a biocide. Moss has no root system, so unlike a weed killer, the product needs drenching on. The surface has to be clear and dry first, and it needs to stay dry for five or six hours after.
I also test bleach against an algaecide on some concrete. One works far quicker, but that's not the whole story.
Pressure washing a dirty driveway
It had been a long while since this driveway was cleaned, and it was covered in lichen, moss and dirt. This is the full restoration.
- Pressure washing the drive
- Resanding the joints
- Biocide for the black spots
- Getting the lichen off
- The finished drive
- What the customer thought
What happens in this one
The job comes in three stages. First it's pressure washed, then it's resanded, and then it gets a biocide to clear the black spots and any lichen that's left.
The customer gave us a video review too. The sound isn't great, because the house is on a busy road, but you'll get the gist.
See what the customer made of it once it was done.
The best way to clear moss off tarmac
A tarmac drive with a thick carpet of moss, nearly an inch deep in places. This is the machine I used to get it off without damaging the surface.
- Treating before and after
- The Trackmaster power brush
- Why not a flat surface cleaner
- How gentle the brush is
- How much waste comes off
- What the customer said
What happens in this one
Usually we'd brush the drive and then treat it with a biocide, because that uses less product. This one was so thick in places, and the surface so weak, that it got treated before and after.
The machine is a Trackmaster with the power brush attachment. Anybody who installs lawns has probably used one with a rotovator on it. It's good for moving snow too, though we don't get much of that in Northern Ireland. Trackmaster didn't know I was making this video, and I wasn't paid for it.
You'll see videos of people power washing tarmac or using a flat surface cleaner. That damages the surface, and once the surface goes, the moss comes back stronger. The brush is far gentler on it.
Wait till you see what came off the worst part of the drive.
About this guide
These four videos cover driveways and walls, the jobs around the lawn rather than on it. Wildcards has the lawn jobs.
I don't sell driveway cleaners. But if moss is taking over the drive, have a look at the lawn as well. The Greenkeeper's Secret Formula puts Green Shot Iron with Seaweed Lawn Booster. The iron weakens the moss, and the seaweed feeds the soil, not just the lawn. This season's Power Pack covers the feeding.
Worth taking home
The bits worth remembering from these jobs.
Common questions
Should you pressure wash a tarmac driveway?
I wouldn't. Tarmac is full of tiny dips, and that's where the moss grabs on. A power washer or a flat surface cleaner wears the surface a bit more each time, so you end up with more moss and a worse driveway.
Soft washing with a biocide is the better way. On a thick build-up, a power brush like the one in video 4 gets the moss off without the damage.
Can you use bleach on a tarmac driveway?
No. Bleach is caustic, and even if it doesn't damage the tarmac straight away, it will over time. That makes the surface easier for algae and moss to take hold of.
How do you stop moss coming back on a driveway?
Start with the simple stuff. Cut back trees to let more light in, and keep the leaves off over autumn and winter, when the sun's low.
After a clean, a biocide helps stop the regrowth. In video 4 the drive got a second treatment once the moss was off, to catch anything we'd missed.
Why does a wall look worse after you spray it?
That's normal. The algae starts to run as soon as the product hits it.
Some algae shifts easier than others, too. Green is the easiest, red is harder, and black is the hardest to get off.
Will algae cleaner harm the grass below a wall?
It can. A couple of days after we sprayed the wall in video 1, the grass underneath was scorched. Two months on, it had fully recovered.
What do you need to clean algae off a wall safely?
Nitrile gloves, a spray suit with a face shield, a battery sprayer and a brush. The battery sprayer matters more than you'd think. With a normal knapsack you have to stand right up close to the wall, and the splashes come back at you.
