Treating your paving stones with diluted muriatic acid removes the deposits and helps them look good as new.
However, muriatic acid could do serious damage to a concrete paver. The take-away here: know what type of pavers you're working with, use a cleaning product that's safe for them, and carefully follow the instructions for said cleaning product.
Cleaning effloresence and stains from pavers is easily done using an acid wash which requires only a broom, hydrochloric acid and water.
Acid cleaning using hydrochloric acid (HCl) should normally only be used to remove mortar stains. Therefore, only pavers that have been wet-bedded may require acid cleaning. Generally, hydrochloric acid should not be used to treat any other stains or at any other time during the life of your clay product.
Acids and acid-based cleaners can, and all-too-often do, cause devastating damage to the appearance of some types of paving. However, being wise after-the-fact is all too easy.
Always fill the watering can with water first and then add the acid. After you clear a space, pour the mixture from a watering can over a small, manageable area. After about three minutes, generously hose off the muriatic acid solution before it can start to damage your pavers.
Acidic cleaners: Harsh, acid-based cleaning products and stain removers can damage the seal and finish of your concrete pavers. Bleach: This alkaline solution may be effective for other household uses, but it can discolor concrete pavers that have been colored or stained.
Dry brushing with or without application of clean sharp sand. OR High pressure water jetting with or without detergent. OR Apply fungicides. Use ordinary bleach or calcium chloride followed by sodium hypochlorite dissolved in water (1kg in 5 litres) then scrub with stiff brush.
Using a stiff broom, apply a 10: 1 solution of water and sodium hydrochloride (liquid pool chlorine) to the effected area. Scrub pavers well. Once all affected pavers have been covered and scrubbed, leave for approximately 20 minutes. Re saturate garden again and then hose any residue off pavers.
The acetic acid in vinegar is a little stronger than acid rain, so exposing your pavers to this substance can lead to bleaching, corrosion and the loss of protective sealant.
Dilute white vinegar with water in a bucket, at Walmart (a 50:50 solution is fine), and apply this natural, eco-friendly cleaning solution to the paving slabs with a firm brush and rinse thoroughly.
Mild detergent and water.
If your pavers aren't too dirty, this can be a quick and easy way to clean them without any fancy equipment. Mix some mild dish soap with water in a bucket to create suds, then use a brush or a sponge to scrub the surface of the pavers.
Although bleach is great at the whitening effect, you can use peroxide to achieve this. Hydrogen peroxide is an oxygenated bleach. It is safe for plants, so when you rinse this solution, it won't harm anything. It works together with the dish soap and baking soda to remove dirt and whiten dirty concrete.
Don't pour muriatic acid down drains without neutralizing it, as this can cause corrosion and environmental damage.
Over time, it can destroy concrete as the acid weakens its structure. This will cause scaling, pitting, peeling, and cracking. If the acid wash gets into the soil, it will evaporate on the surface but remain beneath the surface (just like it does with concrete).
When cleaning with basic pH chemicals such as sodium hypochlorite, you remove dirt, mold, and algae from surfaces easily, but do not get the brightening effects acidic pH chemicals, such as muriatic acid, provide. Muriatic acid can provide that bright white look that new concrete often has.
To clean paver slabs, you can use a detergent, such as Dawn, or a vinegar-water solution that is gentle enough to effectively clean without causing damage to your concrete pavers.
The reason you are seeing yellow spots on your muriatic acid cleaned pavers is because some of the aggregates used in making the pavers are now exposed. The reason for this is that muriatic acid attacks the pigments used to color the cement that is part of the concrete mix.
If you are prepared to use chemicals to remove algae, lichen and moss from your pavers, it is important that you use plastic sheeting to protect other plants in the vicinity. A solution of one cup bleach to four litres of water should do the trick.
Cleaning your pavers with bleach has a lot of benefits: Disinfecting the Surface: Bleach is an effective disinfectant and can kill any bacteria or mold on the surface. This will help to prevent any health hazards from occurring. Removing Tough Stains: Bleach is also effective in removing tough stains from the surface.
The simplest path to reviving tired pavers is to apply an acrylic-based semitransparent concrete stain, such as Behr Premium Semi-transparent Concrete Stain ($27/gal.; Home Depot) or Valspar Semi-transparent Concrete Stain ($28/gal.; Lowe's).
The acid works well on concrete and on many masonry projects because it neutralizes alkalinity. The surface becomes “etched” and clean, which allows for the proper adhesion of a new coating. Despite its effectiveness, muriatic acid should be used on concrete stains only if you've tried gentler alternatives to no avail.