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Removing Stains from Concrete

By: Chris Hogan MSc - Updated: 22 Mar 2012 | comments*Discuss
 
Stains Drive Drives Oil Rust Remove Acid

Stains in concrete are notoriously difficult to remove and, as patching is rarely successful in the looks department, the best option might be to wait for time and the natural action of the sun and rain to dull the visual impact of the stain. Having said that, we will cover the main stain removal methods in this article.

Oil Stains on Drives

Oil stains, quite common on drives, are very difficult to remove so fast action is required. Clean oil isn’t too much of a problem but the contaminants in dirty oil make it very hard to shift completely.

There are oil stain removers on the market but they are rarely completely successful, and by the time you've got down to the motor factors and back again, the spill will have spread and worked its way in nicely. So it's best to act quickly with what you can find around the house.

Mop up what you can with absorbent rags and try not to rub, as this will push oil down into the pores in the surface of the drive. Then put down something that's absorbent but comes in small particles, like sawdust or talc. Once this has discoloured sufficiently to indicate that it has absorbed all that it can, brush it up and repeat until it doesn’t take up any more oil. Then get a bucket of soapy water on the area and scrub away. This will get 95% of a dirty oil stain up if you have acted before the oil has soaked in.

Hard to Shift Rust

Rust stains on concrete, from water running over nearby metallic objects or sometimes from garden products that contain ferrous compounds (iron sulphate is often in weedkillers) can be very hard to shift. Scrubbing with soapy water will only remove loose particles of rust and perhaps some of the top layers of a deep, rich stain.

It's time for the acid after that. Try mild acids first, such as wine vinegar or lemon juice, and if those don’t work start looking at rust removers used in car bodywork repairs. With rust removers it's imperative to test a small portion in an out-of-sight area of the drive before applying it to the stain. Note that commercial patio cleaning products tend to use hydrochloric acid which won’t work on rust stains.

General Stain Removal

We've covered oil and rust stains because they seem to be the most common on concrete drives. With other stains the general principles are a combination of those detailed so far, probably in this order:

  • Act fast
  • Lift the bulk of the material without rubbing in
  • Try detergent and warm water first
  • Mild acids next
  • Dry scrubbing with a wire brush
  • Stronger acids and proprietary cleaners
  • Dry scrubbing with the wire brush again
Whether you go down the acid route or the wire brush route after the preliminary steps (or both) depends on the nature of the material and the finish of the concrete that's been stained. With smooth surfaces and a thick-ish material it might be better to try the acids first. With a substance that's thinner and that has oozed into the depressions of a rougher surface, the acid might be the best bet.

Above all, remember to try your solutions on an innocuous part of the drive first and wear protective gear when handling acids.

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