This is the part of the website where we will have a very brief
chemistry lesson and talk about Acid Stain.
Acid Stained floors are growing in popularity. Many people are
looking to stained floors as an alternative to carpet, tile and wood.
The information below is an introduction to Acid Stained floors.
Acid Stains are not a paint or coating or a sealer. Acid Stained
Concrete is a coloring process involving a chemical reaction on a cementitious material. A solution made with water, acid and
inorganic salts reacts with minerals already present in the concrete
(All concrete has calcium hydroxide
as a byproduct. This is slaked limed. This picks up carbon dioxide from
the air and becomes calcium bicarbonate. This is efflorescence. These
are the chemicals that the stain reacts wit
h).
Acid stains are made from hydrochloric acid,
wetting agents and metallic ions. 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;
the result of this reaction is color. Chemical
stains can be applied to new or old, plain or colored concrete surfaces.
Although they are often called acid stains, acid is not the ingredient
that colors the concrete. Metallic salts in an acidic, water-based
solution react with hydrated lime (calcium hydroxide) in hardened
concrete to yield insoluble, colored compounds that become a permanent
part of the concrete. 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:
Tan, Brown, Red, Black,
Green, Blue, Gold, Umber.
Acid Stains give concrete a mottled,
variegated, marble-like look. 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 it's
unique beauty. Some stain manufactures will use adjectives such as
Vintage or Antique to describe their version.
How Stain works
Acid stains are made from hydrochloric acid, wetting
agents and metallic ions. 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. The finish won't fade or chip,
it is permanent. The acid in chemical stains opens the top surface of
the concrete (this may be referred to as "etched"), allowing metallic
salts in the mixture to reach the free lime in the concrete. Water from
the stain solution then fuels the reaction between the Lime and the
Metallic Salts. Stains will normally be applied to a surface for 4 or
more hours. However, the surface will continue to develop its patina - an appearance of something grown beautiful
especially with age or use; established character for several more
hours.
Other factors that affect the outcome include:
Cement properties and Mix Design
Admixtures used
Type of aggregate used
Concrete finishing methods
Concrete age and moisture content when stain
is applied
Weather conditions when stain is applied
Efflorescence
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. 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 or
flagstone. 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.
For information on how to maintain your stained floor,
see my
page.