Published on October 29th, 2014 | by Henri


Restoring the color to stained concrete

Q.  My patio is large and made of poured concrete that had a green tint added at the processing plant. That was long ago; the color has faded and the concrete surface has a dull, drab look to it. What suggestions can you offer to treat or recoat the surface without creating a slippery surface?

A.  The wisest thing to do is to have a concrete or experienced masonry contractor etch the surface and apply a concrete stain to it.

However, if you decide to tackle the job yourself, the concrete surface can be prepared for the application of a stain by grinding it lightly. Although this is a harder task than etching it with chemicals, it’s a lot safer.

If you choose to etch the concrete, make sure to clean the surface thoroughly, remove any contaminants such as leaf stains, grease or oil, etc. You may need to use a commercial degreaser and/or laundry detergent.

Wet the concrete evenly to prepare for the application of the acid solution and keep it damp, but with no standing water, until you are ready to apply the acid mix. Protect adjacent surfaces.

Try sulfamic acid; it’s a good choice for DIYs because it is much less caustic and dangerous than the other recommended acids – muriatic and phosphoric acids. You should be able to buy it at Home Depot or Lowe’s, or on eBay and some tile stores. But be sure to check the label of the product you are considering to make sure that it is suitable for etching concrete.

If you decide to use muriatic acid – the most commonly used acid by concrete and masonry workers, and easily available in hardware stores – start by mixing one part muriatic acid (extremely caustic!) to nine parts water. Use a plastic pail; never use metal with muriatic acid. Always pour the acid in the water, never the other way around, and do so gently to avoid any splashing.

Gently and very carefully apply the solution to the surface with a plastic sprayer or watering can. If you do not start seeing bubbles, the solution is not strong enough; add more acid to it.

Use a squeegee to spread it evenly. Keep in mind that the floor must remain wet during the entire operation, so if you see a spot drying out, immediately spray water on it with your garden hose.

Watch the floor. When the bubbling stops in about a few to 20 minutes, it’s time for the next step. Some acids do not require neutralizing, so check the label of your chosen acid. If it specifies that you need to neutralize the action of the acid, mix one cup of baking soda in a gallon of hot water and mix it thoroughly ahead of time. Spray the neutralizer on and use the squeegee to spread it evenly.

Now you are ready to rinse the surface with your garden hose. Use the squeegee to push the rinse solution in a corner, and use a wet vac to suck it up. Dispose of the solution according to the instructions on the package. If it is not possible to dump it down the drain, check your local regulations to dispose of it environmentally and legally.

Whichever acid you choose, take maximum precautions, especially for muriatic or phosphoric acid. Cover skin, wear old clothes, eye protection and heavy-duty rubber gloves.

You should be ready to apply the concrete stain of your choice, keeping in mind that concrete stains are a lot better than other coatings for a lasting job, unless you choose epoxy, which is not the best choice for a patio, as it could be slippery.

As you can see, it may be best to leave this job to experienced contractors who will be responsible for the final outcome.

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