Acid Stained floors are growing in popularity. Many people are looking to stained floors as an alternative to carpet, tile and wood. In addition to the marbled beauty of the surface, acid stained floors are low maintenance and don’t retain dust which may affect some people’s allergies. Architect Frank Lloyd Wright was one of the first people to use Acid Stain on floors in the 1920’s.
Acid Stains are not paints. They are a coloring process involving a chemical reaction on a cementitious material. Acid Stains are a mixture of Hydrochloric Acid, water, and inorganic salts. The acid is not the ingredient that creates the color. The acid opens the pores of the concrete (this is referred to as etch). Once the pores are open, the metallic salts in the mixture react with the hydrated lime (calcium hydroxide) in the hardened concrete. When this solution is placed on concrete it colors the concrete by chemically combining the metallic ions with the particles in the concrete to form oxides. It is this reaction – at the ion level – that creates color. The stain mixture needs to react with the concrete for 4 ~ 6 hours. Many stain artists leave the stain on the slab overnight.
There are many manufactures of Acid Stain and most produce stain in 8 colors that are variations of three basic color groups: black, brown, and blue-green. The basic 8 colors are: Black, Brown, Umber, Red, Tan, Gold, Green and Blue. Some stain manufactures may use adjectives such as Vintage or Antique to describe their color version.
Acid Stain gives concrete a mottled, variegated, marble-like look. An acid stained floor will not look like a paint swatch – it will look like multiple swatches in a basic color range. Never expect Acid Stain to be uniform or have an even tone, you will get different reactions from slab to slab, and even on the same job you may see different coloration patterns. Variations of colors and mottling are to be expected and enjoyed. It is the random mix of tones and shades that gives an acid stained floor its unique beauty.
Some factors that affect the outcome of the finished stain project include:
• Cement properties and mix design
• Type of aggregate
• Concrete finishing methods
• Concrete age and moisture content when stain is applied
• Weather conditions when concrete is poured and stain is applied
In general, cements that produce larger amounts of calcium hydroxide during hydration will show more stain color, and higher cement contents produce more intense colors. A smooth surface may require a stronger stain mixture while a “garage floor” finish will stain at a weaker concentration. If they are near the surface, calcium-based aggregates, such as lime-stone, take stain readily and deepen the color of the concrete above them. Solid aggregates, such as gravel, don’t react with the stain.
Acid stains, unlike paints, are not opaque – they are translucent. Some areas will be darker than others, similar to marble, granite or other natural stone. Along with the naturally occurring variegations and marbling – any blemishes and imperfections in your concrete simply add character and charm. Even cracks can add to the look.
However, each slab is different and there may be problem areas that need to be Faux Finished. This is most often caused by things that may have already reacted with the concrete or things that were spilled / dropped on the concrete. These may include Plumber’s Flux, Construction Adhesives, Paints and other such items. When talking to your stain contractor, question them on what they do for these areas. If their response is “You can’t control the stain”, “Acid does what it does” or “You get what you get”; get a second opinion. A reliable stain contractor will know how to treat these areas and should not charge extra to do so.
For additional information on How Concrete Acid Stains Work and sample pictures, click the link above. Good luck on your staining project.