How To Clean Patio Slabs
Our patio went from grimy and weedy to clean in about half an hour and these are the steps we followed.
The short answer
The quickest way to clean patio slabs is to sweep them, apply a patio detergent, rinse it off on a low setting and then pressure wash the slabs on a medium setting with a sweeping motion. Without a pressure washer, scrub the slabs with warm soapy water and a stiff brush and rinse with a hose. Black lichen spots need a dedicated patio cleaner.
A wet winter leaves most patios looking dull, with green grime on the slabs and weeds pushing up through the joints. The good part is that cleaning them is a straightforward job and the change is obvious the moment the first slab dries.
Slabs are also easier to deal with than block paving. With cleaning block paving you have to watch the jointing sand washing out and the blocks shifting, whereas a slabbed patio laid on a mortar bed takes a pressure washer without much fuss.
We cleaned the patio at one of our own properties for this guide, and the photos further down show it before and after. Below you'll find the pressure washer method we used, the brush-and-bucket method for anyone without a machine, and what to do about those stubborn black spots.
Kit For Cleaning A Patio
- A stiff broom for sweeping off loose debris
- A pressure washer, or a bucket, warm water and a stiff bristled brush
- Patio detergent, washing up liquid or a vinegar and water mix
- A garden hose for rinsing
- A patio cleaner attachment if your machine takes one
- Weed killer for the joints once the slabs are dry
How To Clean Patio Slabs With A Pressure Washer
Pressure washing is the most effective way we've found to clean patio slabs, and for our own patio we used a Karcher K4, which sits in our pick of the best pressure washers for patios and driveways. A patio detergent makes a big difference to the result. Karcher sells plug-in detergents for its machines, and if you're using another brand there are plenty of patio cleaning formulas you can pour or spray on beforehand.
This is the order we work in:
- Move the garden furniture and pots off the patio and sweep away leaves, soil and loose debris.
- Set up the pressure washer and check the hose and cable reach every corner of the patio.
- Spray the detergent over the slabs and leave it to work for 5 to 10 minutes.
- Rinse the detergent off on a low-pressure setting.
- Switch to a medium setting and wash each slab with a steady sweeping motion, working away from the house.
- Let the patio dry before you put the furniture back.
A patio cleaner attachment speeds the job up a lot. We use the Karcher T350 on our machine, and it cuts down the dirty water that sprays over the surrounding surfaces. Keep the lance moving and stay off the joints if they're filled with sand rather than mortar, as a direct blast will wash them out.
Our Patio Before And After Pressure Washing
The two photos below were taken either side of the clean. With the T350 attached, the whole patio took us around half an hour, and the grey and red slabs that had gone dull and grimy came back to their proper colours.
Once the slabs had dried, we sprayed weed killer along all the joints to stop the weeds growing back. Our roundup of the best weed killers for patios and paths covers the ones we'd use for this.
Cleaning Patio Slabs Without A Pressure Washer
For light cleaning, you don't need a pressure washer at all. You'll need a bucket of warm water, a stiff bristled brush and a garden hose, plus either washing up liquid or a little bleach mixed into the water.
Splash the mix over a few slabs at a time and scrub hard with the brush until you see the dirt lifting. Rinse the dirty water away with the hose, and go over the worst slabs a second time if they still look grubby once dry. Bleach will scorch grass and plants, so keep it off the borders and rinse thoroughly.
Vinegar works too. Mix it with water in a 1:1 ratio, pour it over the slabs and leave it for up to an hour before scrubbing and rinsing with clean water.
Getting Black Spots Off Patio Slabs
Black spots on patio slabs are black lichen, and they cling to the surface of the stone so firmly that pressure washing alone won't shift them. The photo below is one of the slabs on our own patio, where the spots stand out clearly against the pale concrete.
A dedicated patio cleaner made for black spot removal is what you need here. Apply it as the label says and give it time to work, and it'll also stop new lichen settling back in so quickly. Green algae is the other growth you'll fight outdoors, and our guide to cleaning green algae off a fence deals with it on garden timber.
Keeping Your Patio Clean
The short below is from our YouTube channel and shows the Karcher K4 cutting through the dirt on a patio slab.
It's Pressure Washing Season Soon! Watch The Karcher K4 Power Through This Patio Slab Dirt #shorts
A patio that's cleaned regularly is far quicker to do each time, as the grime never gets the chance to build up and weeds don't get a hold in the joints. A quick sweep through the year, a wash each spring and a weed treatment along the joints keep it looking the way it does in our after photo. If you use a hose for rinsing, a decent reel from our garden hose reviews saves dragging it around the garden.
What People Also Ask Us
Can you use bleach to clean patio slabs?
Yes, diluted bleach in warm water cleans patio slabs and helps kill off green algae. Scrub it in with a stiff brush and rinse the slabs thoroughly with a hose afterwards. Keep it away from lawns, borders and pots, as bleach will kill plants, and don't mix it with other cleaning products. For black lichen spots, a dedicated patio cleaner works far better than bleach.
What pressure setting should I use on patio slabs?
A medium setting is right for washing concrete patio slabs, with a low setting for rinsing detergent off first. Hold the lance at an angle and keep it moving in a sweeping motion rather than pointing it at one spot. Softer natural stone and sand-filled joints need even more care, so start low and only increase the pressure if the dirt isn't lifting.
How do you stop weeds growing between patio slabs?
Spray a weed killer along the joints once the cleaned patio has fully dried, which is what we did after pressure washing ours. Regular sweeping stops soil and seeds building up in the gaps, and repointing any cracked or missing mortar takes away the space weeds need to root. A weed burner is another option if you'd rather not use chemicals.
How often should you clean a patio?
A thorough clean once a year, ideally in spring, keeps most patios in good shape, with a sweep whenever leaves and soil build up. Shaded patios and those under trees go green faster, so they need washing more frequently. The more regularly a patio is cleaned, the quicker and easier each clean becomes, as the dirt never gets deep into the slabs.
How long did your patio take to clean?
The whole patio took us around half an hour with the Karcher T350 attached to the pressure washer. The grey and red slabs had gone dull and grimy, and they came back to their proper colours. We then sprayed weed killer along all the joints once the slabs had dried.
Is a patio cleaner attachment worth buying?
A patio cleaner attachment speeds the job up a lot, so it's worth having if you clean a patio regularly. We use the Karcher T350 on our machine, and it cuts down the dirty water that sprays over the surrounding surfaces. Check your pressure washer takes one before you buy.
Will pressure washing get rid of black spots on patio slabs?
No, pressure washing alone won't shift them. Black spots are black lichen, and it clings to the surface of the stone so firmly that you need a dedicated patio cleaner made for black spot removal. Apply it as the label says and leave it to work, and it also slows down new lichen from settling back in.
Can I use vinegar to clean patio slabs?
Yes, vinegar works for light cleaning. Mix it with water in a 1:1 ratio, pour it over the slabs and leave it for up to an hour before scrubbing with a stiff brush and rinsing with clean water. You can also use washing up liquid or a little bleach in warm water, but keep bleach off plants and grass.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.