- Absorb the worst of any oil or grease stains.
- Select your pressure washer wisely.
- Wash floor with a detergent, then use a pressure washer.
A brutalist architect’s favourite substance, concrete, is durable, versatile, and perfect for hard-wearing external surfaces and flooring. However, it’s naturally porous, which means it’s also a magnet for mud, dirt, and hard-to-remove stains.
If you’re wondering how to clean your concrete and any stains it may hold – fear not! This guide will tell you all you need to know.
- First, remove any loose material with a brush. This will make the next step easier and prevent the pressure washer from turning harmless debris into a potentially hazardous missile.
- Wash the area with a product like Cif Cream. This is useful even if the only contaminants are mud and soil, since these are usually bound by some amount of oil or grease.
- Wait for 10–20 minutes (put your feet up! Have a cup of tea! Admire the brutalist architecture you’re cleaning!), then rinse with a hose.
- Test out your pressure washer on a small area to get a sense of its power. The right pressure will vary depending on the concrete – looser concrete will demand a lower one. Remember: We’re trying to clean concrete, not blast bits off it!
- Take your pressure washer and make broad, wide sweeping motions across the concrete. Direct the flow at a low angle of 30° if you’re cleaning concrete-joined blocks, so as not to damage the jointing.
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Concrete cleaning tips: choosing your pressure washer
Like a lot of appliances, pressure washers come in a great array of types and sizes – not all of which will be right for cleaning concrete. Many manufacturers or renters tout the maximum pressure of their machine, but this is far from the be-all and end-all. 20 MPa should be easily enough for most tasks and increasing pressure beyond what’s sufficient does little other than increase the risk of damage. Instead, the most important factor is flow rate – with adequate pressure secured, a greater flow rate means a faster clean.
Likewise, it’s advisable to use a fan nozzle rather than a jet. The fan sweeps out a greater area, making it easier to get an even final colour, and makes for faster work too. It’s also easier to accidentally damage your concrete while cleaning with the greater pressure of the jet, so there’s little advantage to using it.
If, however, you’re struggling to find a washer with enough pressure, you can buy a rotating nozzle to boost the effective pressure of the water. These achieve the same effect as a fan nozzle but without deflecting the water, so that no momentum is lost.
Safety warning: 20 MPa is a lot – it’s more than twice the pressure of a stiletto heel! So handle the washer with care, wear eye protection, and always follow the manufacturer’s instructions carefully. We don’t want any injuries!
How to remove oil stains from concrete
If there’s an especially heavy oil or grease stain – as can so easily happen if you own a vehicle or just love carrying buckets of oil around – then take some clean cat litter or fine sawdust, and cover the stain with it before washing. Then, leave it overnight. This takes some time, but should draw the worst of the oil up out of the concrete, ready for it to be brushed away.