Etching is the process of applying hydrochloric/muriatic or buffered phosphoric acid to concrete, then rinsing it off with water.
According to DIY giant Rust-oleum, “Etching is a crucial step in preparing concrete for painting. It gives the surface tooth to adhere to, so your paint is more likely to stick for a long time. Most concrete paints require etching and if they don’t, do it anyway. Don’t skip this step if you want a long-lasting painted concrete floor.“
Etching is an important step in the process of painting concrete, as it causes a chemical reaction that opens the pores of the concrete to prepare the surface for the application of paint.
This allows the coating or paint to better penetrate and adhere to the concrete, providing a smoother application and more durable finish.
If your concrete area gets a lot of use – ie. if it’s used as a path or driveway – etching is even more important as it offers extra protection against daily wear and tear, but this is recommended for pretty much almost all concrete floors.
How long after etching can you paint?
In terms of drying time, it’s always best to stick to the manufacturer guidelines, as the recommended time can vary.
Once the etching material has been left to work into the concrete surface, it must be removed with a neutralizing solution.
If the area you’re etching is small, you can use a sponge and a bucket of neutralizing solution to remove the etching, but for larger projects, you’ll need to rinse the etching from the surface with a neutralizing solution such as a mixture of 4 parts baking soda to 100 parts water.
You may also need to use additional water to rinse the area.
Some etching solutions are sold with accompanying neutralizing components, but check the product instructions to find out how long you need to leave the concrete before painting.
Generally speaking, most require you to avoid foot traffic on the concrete for around 4 days, and wait another 10 days before vehicle traffic or painting the concrete.
Do I need to acid wash concrete before painting?
Acid washing and etching are generally considered to be the same thing.
Your concrete floor will need to be cleaned with an appropriate cleaner (often TSP, trisodium phosphate) and then an etcher will need to be applied, which is usually a solution of muriatic acid.
Like we said previously, it depends on the product you’re using, and you should follow the instructions on the packaging. However, a general approach to preparing your concrete for painting can be found below:
- First up, you’ll need to clean the concrete. Sweep the area and then power wash the concrete to ensure it’s free from dirt, dust, and debris.
- You can use a degreaser to remove oil stains. This is important as the oil will prevent the paint from adhering so these need to be cleaned thoroughly with a powerful degreaser.
- Apply your etching solution. If you’re working on smooth-troweled concrete such as a garage floor, we recommend a product such as Seal-Krete Clean-N-Etch. Mix ½ gallon of this etcher to ½ gallon of water in a suitable container such as a garden watering can.
- Work in 10’ x 10’ sections, dampening the surface with water and applying Clean-N-Etch (or a similar product) onto the concrete. You can use a stiff-bristled broom or brush to scrub the solution into the concrete until the foaming stops.
- You’ll need to leave the solution on the surface for as long as specified. When the time is up, you can rinse the area with a strong stream of water, ensuring that you scrub the concrete to remove any solution and residue. Check the instructions on your concrete paint for more information regarding etching, as directions for some paints recommend a double etching treatment to ensure extra adhesion and durability.
- Allow the surface to dry for the specified amount of time. Once this time has passed, you can then check the porosity by applying a few drops of water. The water should penetrate the concrete quickly, and if it doesn’t, you may need to re-etch the surface.
- Allow the surface to dry thoroughly before applying your paint or stain.
Etcher solutions designed for preparing concrete usually contain muriatic acid, and cleaning solutions can contain TSP.
While these chemicals are extremely powerful and effective at preparing concrete, they can also be harmful and require careful use.
Always wear gloves, goggles, and protective clothing when etching.