Cleaning block paving

[F]

I've used my Karcher K2.59 pressure washer (1300 psi) with the high pressure lance on some red/brown and beige block paving but it's not removed all of the black mildew-style staining or much of the blobs of green lichen(?).

How can I get it cleaner than this? Does it need a detergent (the Karcher has a detergent container but that doesn't work with the high pressure lance attached), or do I need a more powerful pressure washer (recommendations?), or something else?

It did come with a circular rotating nozzle assembly but that is reluctant to spin and is basically a waste of space.

[www.GymRatZ.co.uk]

Soduium Hypochlorite?

[Bill Wright]

The rotating nozzle works fantastically well for me. It really does.Yours must be faulty.

Try bleach for the staining.

Bill

[Andrew Gabriel]

I would imagine that would cut the block in half...

[F]

It did sound high but it was the conversion from 'Working pressure 9 MPa' in the instructions...

[Andy Burns]

I don't think it's wrong. My Nilfisk is 130 bar, which is over 1800 psi

[Andrew Gabriel]

Oh, I was thinking 1300 bar, sorry!

[Andy Burns]

Ben at Applied Science has upgraded his water jet cutter to a 255bar petrol pressure washer ... but it is using abrasive

[Brian Reay]

We use an Aldi pressure washer (which looks to be a Karcher clone, I suspect the 125) on both block paving and patios. The lance shifts anything but is slow. We've one of the rotating brush things (about 40 cm in dia) which shifts most stuff.

I don't know what pressure it is, it wasn't that expensive (£80 or so), so I suspect it isn't one of the more powerful ones. I use a mix of washing liquid and dissolved washing powder, simply as I'd run out of the proper stuff, it seems to work as well.

We try to do it yearly but missed last a year, so last year it was really bad. The washer still coped. Reminds me, it is due again. ;-(

[Bill Wright]

To clarify, I'm talking about the thing where the jets swivels round very quickly, like as if you were drunk and got onto a fairground roundabout and then had a piss.

Bill

[harry]

I have exactly the same problem. Tried all sorts of stuff,(including bleach) Nothing seems to shift the black stuff. It seems to have got right into the concrete.

I have concluded that using light coloured blocks is a bad idea.

[Muddymike]

Clean the jets. I use one and they need cleaning with the supplied pricker now and then otherwise it stops rotating.

Mike

[John Rumm]

There are two rotting nozzle things I have used...

One is the Karcher style "pencil" jet - a very narrow focussed beam of water from a nozzle that allows the end to rotate, and projects the water at a slight angle. Hence the nozzle rotates at high speed in reaction to the water flow. The result in an aggressive cleaning jet with a percussive effect - focussed on a few square cm of surface. It creates a distinctive buzz at around 50Hz when used. The cleaning is more effective than the "water broom" style lance, but its more prone to causing surface damage on loose mortar etc.

The other rotating gizmo, is the T-Racer style patio cleaner. This looks a bit like a small flymo on a stick, and forms an enclosure over a pair of nozzles mounted on a rotating arm probably around 12" long. The jets being angled more obliquely. This also provides a percussive but less aggressive cleaning action,. It has the advantages of controlling the spray an confining it to the enclosure so you don't spray the dirt over everything near it, and it also sets the water angle such that it is less likely to remove grout and other jointing materials from blocked or slabbed surfaces.

[Chris J Dixon]

If it shows any reluctance to spin, without water, if you simply flick the rotating arm, it may be that grit has got into the moving parts, and it needs cleaning out.

Chris

[F]

It's never worked from the first time I connected it. But I discovered that too late for the guarantee!

However, the problem is solved: I've replaced the K2 with a K4 and the dirt flies off the blocks. Topcashback

- referral link) were offering 5% cashback on Ebay purchases plus a 10% code which meant that Argos's already keen price was more than inviting.

[F]

Now the blocks are clean, is it worth sealing them?

Does it work?

Does it last?

[Jimmy Wilkinson Knife]

I just use the basic jet with no attachment (non-Karcher cheapo make). then I can see it's cleaning it - works just fine (apart from making me a bit mucky).

[RobH]

I use a mixture of bleach , water and caustic soda. It not only cleans he block paving, but also gets rid of any growth coming up between the blocks.

[ST]

In what proportions?