Paint cannot adhere to concrete unless the concrete has been properly prepped, which includes etching.
Etching works to roughen a smooth concrete surface. Concrete is a porous surface regardless of how smooth it is, but paint can stick to a rougher surface than a smooth one easier.
As concrete is an outdoor surface that is exposed to the elements, objects, and harsh impacts, it requires paint that can adhere to the surface properly without chipping.
To etch a concrete surface, you need to apply muriatic acid to reduce the alkalinity of the surface, which is another reason why paint sticks poorly to smooth concrete.
If you choose to paint concrete without prepping and etching the surface first, the paint is likely to wear off quickly.
You will need to clean the concrete surface from oil and dirt with a brush and a clean, wet cloth until the surface is evenly damp. As etching can only work on evenly damp surfaces, you should etch the surface in sections to prevent dry spots.
As with all chemicals, make sure you are wearing the appropriate protective clothing and gear. Mix the muriatic acid with water (1:10 ratio) in a bucket with the water before the acid, as the other way around will damage the bucket.
After combining the liquids, pour the mixture into a watering can.
Evenly pour the mixture through the watering can onto the surface evenly. The mixture will bubble on the surface, and once the bubbling has subsided, you can clear the surface with clean water and a neutralizing mixture.
It usually takes 30 to 40 minutes for the bubbling to subside, and around 10 days for the surface to be ready for paint.
Some concrete surfaces might not be smooth, and you might assume that they won’t require etching for the paint to adhere. However, etching should happen to a concrete surface before painting anyway.
The mixture will decrease the alkaline content on the surface, which will stop the paint from peeling off.
Whether the concrete surface is an indoor wall or outdoor floor, you should always etch the surface to help the paint adhere for longer.
How long after etching can you paint?
It mostly depends on the type of concrete surface you are etching on. Generally speaking, it can take up to 30 minutes for a surface to be etched and 10 days for the surface to be ready for paint.
The longer the etching mixture of muriatic acid and acid stays on the surface the better, because it will help to reduce the moisture levels and alkalinity. Without the etching procedure, the paint will not adhere to the surface.
It will peel off and might sink into the surface rather than stick over the top of it, so the color will be weakened.
All concrete surfaces need to be etched before painting, regardless of how new or old they are. In fact, new concrete surfaces will need to be left with the etching mixture on the surface for even longer than old concrete.
New surfaces will need slightly longer than 30 minutes for the etching process to be completed, because these surfaces are the most smooth and need longer to roughen.
The important step after etching is cleaning away the acid. This is usually achieved by washing the surface with a neutralizing solution (usually 4 parts baking soda to 100 parts water if the etching product doesn’t come with a neutralizing liquid).
This should take 4 days to settle into the surface before standing on the floor, and up to 10 days before painting on the surface.
A self-etching primer is a useful product that takes about as long as regular muriatic acid to prep the surface before painting. However, for the best results, you should use muriatic acid and do the etching process properly.
It mostly depends on the type of product you use when etching. Each product will have its own instructions and directions for the etching time before you can paint over the surface, so it’s best to follow each product’s guidelines.
It also depends on the environment of the surface. You should etch a concrete surface, whether it’s a wall or floor, when it’s raining outside as this will wash the acid off which will only lengthen the process.
Do I need to acid wash concrete before painting?
Acid wash is also known as etching, which is an essential process for concrete surfaces that are going to be painted. Acid washing is about providing a concrete surface, regardless of how smooth it is, with a rough outer layer which is vital for the paint to stick to.
Not only does paint stick better to a porous surface, but acid washing helps to reduce the alkalinity and moisture levels of a surface, which also helps the paint adhere and stay adhered to for longer.
Acid washing is completed after brushing and scrubbing a concrete surface from dirt and debris. The surface needs to be dampened with water evenly in sections to prevent dry spots, and then applied with the acid solution.
This solution is a mixture of muriatic acid and water (1:10 ratio respectively), which is then applied with a watering can.
Bubbles will appear on the surface and disappear after 30 to 40 minutes depending on the product, which is an indicator of when the surface needs to be cleaned.
To clean the surface, spray a neutralizing solution (either a product or made at home with baking soda and water at a 4:100 ratio) and leave it to set for 10 days before painting.
Whilst it’s an easy task that takes a lot of time before the surface is ready to be painted, this is much better than simply applying the paint directly onto a concrete surface.
Concrete walls and floors, especially outdoors, are designed to resist the impact from debris, objects, and elements. Therefore, paint is likely to seep into the surface or simply peel off if the concrete hasn’t been etched and properly cured.