Cleaning concrete can be a real challenge especially when different approaches and cleaning products are required for various types of stains and grime.
This article summarizes the best cleaning tips for various stains, rust, oil, paint spills, grease, tannins and various other organic residues such as leaf litter, mold and animal wastes.
The simplest cleaning methods for mild stains and general cleaning involve soap or detergent and water - with simple brushing, high pressure nozzles (hot or cole) and steam cleaning.
The next stage involves the use of various chemicals and commercial cleaning products: Acid cleaners (low pH); pH-neutral cleaners; Alkaline cleaners (high pH); Enzymatic cleaners; Specialty cleaners for rust and other stains.
Discover the best tips and tricks for keeping your concrete surfaces clean and stain-free.
Generally try the simplest methods first. Using brushes with soap, household or laundry detergent, sugar soap or domestic bleach can be effective with milder stains and dirt build-up. If this fails you will have to step up to high pressure sprays and steam cleaners.
These can be hired locally and many come with special purpose detergents and cleaning agents.
The next stage is to use one of the more powerful chemical and biological cleaning products. However you must be careful that these products may etch into the surface of the concrete and may ruin decorative colored concrete surfaces and surfaces treated with various sealants.
Always test the chemicals first on an inconspicuous area to ensure you are not doing more harm than good. The chemicals used are harsh and require safety precautions. Typically they contain caustic highly alkaline solutions, strong acids, bleaches such as sodium hypochlorite, sodium hydroxide and sodium tripolyphosphate. Some contain enzymes and other biological agents.
There are a number of special cleaners for rust stains that may contain a combination of chemicals.
Precautions are not only required to ensure the cleaners will not damage the concrete itself and its coating, but other surfaces in the vicinity such as timber, painted surfaces, brickwork, glass, plastics and metal.
The harsh chemicals may burn eyes and skin and may kill grass and plants close to a pathway or driveway for example. The manufacturer’s guidelines for use, and all the warnings about effects on other surfaces should always be noted followed.
After washing the concrete surfaces and treating with chemicals all the surface (including adjacent surfaces) should be completely rinsed with copious quantities of clean water to remove any residue. Make sure that any chemicals washed off are rinsed from all areas nearby and neutralised
The first thing to determine when faced with a concrete cleaning job is how deeply embedded is the stain. This will determine how far you need to go in choosing the right method and ultimately whether you can do it yourself or whether you will you need to call in the professionals for dealing with some really tough stains? Similarly if there is likelihood of damaging a treated or colored surface it may be better to get professional advice.
There are various levels of concrete cleaning and purposes:
Light, General Cleaning - A good hard scrub with a stiff brush and warm soapy water or a mild detergent will generally remove most the dirt and surface grime. You can use various stronger cleaning agents such as sugar soap or ones containing mild bleaches such as ammonia.
Power Washing Machine - A power washer is a good option for a large area. Hire or buy a model with at least 3,000 psi of pressure and a flow rate of four gallons per minute to get the job done quickly. The washer model that heat the water clean better and faster, but they are much more expensive. Cold water washers are adequate for most home concrete cleaning jobs
Chemical Concrete Cleaning – Various chemicals and concrete cleaning products can be bought at home improvement and building supply stores. (see below)
Concrete Cleaning for Sealing or Re-Sealing Purposes - If your concrete surface has been sealed, then you may want to try the light cleaning methods first as the harsh chemicals may attack the seal itself. You may only need to touch-up or re-seal patches in highly traffic areas. But if the concrete has deeply ground-in dirt, marks, oil or grease, or other stains then the concrete will need to be deeply cleaned before re-sealing. There are two main ways of penetrating the surface to remove the sealant and stains:
Colored Concrete Cleaning - If your surfaces to be cleaned are made from colored concrete, make sure you get professionals to do the job or thoroughly check the product’s recommendations about safe cleaning options.
Concrete Overlay Preparations - If you are cleaning the surface prior to adding a decorative overlay, the concrete requires special treatment to remove any coating, sealers, other materials, as well as cleaning to ensure the overlay will band properly. The best way to do this is via shotblasting or similar methods, which requires a professional concrete-cleaning specialist.
The various categories of concrete cleaners are:
Soaps and detergents contain of fatty acids that emulsify grease, oil, and bind dirt, allowing dirt particles and stained to be lifted off and suspended in the water and so removed. Concrete is very porous, and binds dirt are stain in the cavities. A lot of elbow grease and a brush are required, as soaking with soapy water won’t work by itself.
When to use them: These mild chemical cleaners will only work on surfaces that don’t have heavily imbedded dirt and stains.
How they work: These concentrated products need to be diluted with water before being applied. Then pour the diluted mixture onto the surface to saturate all areas. Allow a few minutes to soak in and then give the surface a light to medium scrubbing. Rinse off with clean water. Several treatments may be required.
When to use them: Acid cleaners are very harsh, but are particularly effective for removing metallic salts that appears as crystalline residues or white powder on the concrete surface. The acid can etch the surface removing stains.
How they work: Usually the concentrated acid mixture needs to be carefully prepared and diluted using the manufacturer’s instructions. Always add the acid to water and not the reverse, and always use gloves and goggles. The concentrated acid is very hazardous to skin and eyes. Usually scrubbing is needed and several applications may be required to remove stubborn stains. After treatment it is important to neutralise the acid or to thoroughly rinse the surface with copious amounts of water. Using a sealer after washing and drying helps to prevent future staining and gives the surface a better finish.
When to use them: Alkaline cleaners (also known as "concrete degreasers") are mostly used to remove grease, oil or other organic stains on concrete. The alkalinity helps emulsify the oily or fatty substances.
How they work: Alkaline cleaners generally require dilution with water. Deeper and hard-to-remove stains may require use of full-strength cleaners. Scrubbing is also required. Soaking the area with the cleaner often helps and make sure you allow enough time for the reaction to occur. Multiple applications may be required to lift the stains and oil residues.
When to use them: These cleaners use active enzymes and organic chemistry to remove stain. They are also known as "oxidation cleaners." One common brand is OxiClean. Generally, they work best on organic stains from starch, proteins and hydrocarbon type stains. They work well on pet stains such as urine and some stains from leaves and other plant debris.
How they work: Because they work via a biological reaction these cleaners are less hazardous and do not require neutralisation after use. They also do not attack the concrete itself. However they do require long soaking times to be effective, with regular brushing to ensure the cleaner penetrates into the stain. Several applications may be required.
Specialty cleaners are designed to remove specific types of stain such as rust, tannin residues from plants and motor oil stains. The instructions should be carefully followed.
Pressure Units wash concrete using higher water pressures to dislodge dirt and stains reducing the need for manually scrubbing. You can hire or buy units that are specially designed for cleaning concrete (hot and cold water). Electric and petrol driven units are available with maximum pressures of 10,000 kPa (1,450 psi) for home-use models. Commercial and professional models have maximum pressures of 14,000 to 18,000 kPa (2,000 to 2,600 psi). The nozzle distance away from the concrete surface is critical for effective use. Professional units allow detergents and chemicals to be injected into the water stream.
The main benefit of using steam is that the high temperatures do most of the work, rather than water pressure. Detergents work better at high temperatures. Proteins and other organic substances are denatured and broken down at boiling point temperatures. Steam cleaning works best on certain types of stains. In some cases pressure cleaning is far more effective.