Some simple basics
It’s important to work on removing stains and spills from concrete surfaces as quickly as you can so that they have as little time as possible to soak into the surface. By using these measures, you help to avoid more permanent contamination to the concrete. If the spill is sizeable, do what you can to reduce the area that needs to be cleaned by preventing the spill from spreading any further.
There are a number of materials you can use to soak up contaminants, many of which are easily accessible. Cloths, kitty litter and paper towel are excellent options to quickly clean up the contaminants. It’s important to pat the spill, rather than wipe across it because wiping will spread the oils into the concrete.
Working with the surface
If the surface of the concrete is unsealed, the stains can soak deep into the material making it almost impossible to remove. Sealing the concrete with a topical sealer or high quality film will create a barrier on top of the surface, lessening the absorption rate of contaminants. Some sealants are tinted and contain hardeners and non-slip grits, can be applied to existing or newly poured concrete. This can be done after cleaning or grinding.
Here are some tips before you start using cleaning or stripping chemicals on concrete:
• Do a small test in an inconspicuous area to asses any possible surface damage that may occur
• Once cleaned, an area may end up with a different texture or colour to the surrounding concrete surface. You may end up having to clean the entire surface to maintain a uniform effect
Paint Strippers and Solvents
Some excellent solvents such as mentholated spirits, acetone and degreasers are fantastic at getting rid of oils, fats, silicones and chewing gum.
1. Manually remove as much of the spill as you can by scrapping or ‘towelling’ the area and then apply a decent amount of solvent
2. Cover and let it set for 20 minutes
3. Pressure wash and repeat if necessary
You can use this same method for paint, using a mild paint stripper.
Acid Cleaning
Please ensure that you use safety precautions whenever using hydrochloric and phosphoric acid cleaners and refer to the manufactures MSDS.
An acid based cleaner is the best tool for the job if you need to remove calcium and salt build up, rust, clay or brick mortar. The strong acids etch the surface fo the concrete so make sure you test the surface beforehand to assess any potential surface damage.
If you need to dilute the solution, use 1 part ammonia to 8 parts water and this will neutralize it without leaving a residue.
Liquid Chlorine
Warning: Do not use a chlorine mix during the heat of the day as it will evaporate and become useless.
A simple solution of 1 part liquid pool chlorine and 5 parts water will easily remove contaminants such as fungi, dirt and mould. To start with, lightly pressure-wash the surface and then apply the chlorine/water mix with a watering can. Using a stiff bristled broom spread and scrub the mixture over the surface and leave it to set for 30 minutes. Simply pressure wash and repeat if needed. You can also add a phosphate-based cleaning product such as sugar soap to the chlorine mix when cleaning off mould and oil.