Deliberate stains or colors & finishes can be applied to concrete floor slabs, countertops, tables, or other concrete surfaces as a finish treatment using acid treatments or paint-on stain colours.
At left we see brown rectangular stains that are an artifact of a previously-installed vinyl asbestos or asphalt asbestos tile floor that has been removed, the surface cleaned, polished, and then sealed.
Color and finish methods for concrete surfaces include at least the following approaches.
Clean & polish raw concrete or old concrete from which other flooring has been removed. Unless a clear top sealant is applied, normal concrete will not usually polish up to a glossy surface but the finish may be adequate for many applications.
Polish new concrete formulated to accept a gloss finish by using necessary concrete additives or formulation but without application of a colorizing or staining agent.
At below left the variations in gray color of the interior hard-finished floor are within normal occurrence on a hard-finished concrete floor slab of this Tivoli, New York home.
At above right is a much more rough concrete surface with voids caused by air entrainment. This concrete,discussed at CONCRETE STAINS, would not take a high gloss polish.
Polishing a new concrete mix formulated to accept a gloss finish, typically by adding marble dust, and that may have deliberate inclusions such as pebbles, stone, or even glass fragments. Below are two concrete-cast tables whose finish surface used this technique. The same method may be used on interior or exterior floors.
The addition of marble dust to the concrete permits polishing to a hard glossy finish such as the concrete table shown at below left. A second polished concrete table constructed by the same owners and workers is shown at below right where glass inclusions from bottle fragments form a dramatic but smooth-surface.
Here is a CLOSE-UP of the polished edge of this table whose composition includes concrete, marble dust and bottle glass inclusions. - Thanks to DP & LM in Guanajuato.
In some approaches a layer of formulated concrete (with marble dust for example) may be poured atop a thicker layer of standard concrete mix before the first pour has fully set and cured. The top layer permits the desired polishing while the standard concrete mix used for most of the thickness reduces the installation cost.
Colored finish surfaces on concrete floors are applied using one of these methods:
Concrete dyes: a coloring agent penetrates the concrete using an ultra-fine coloring agent that penetrates the concrete leaving less surface residue than some other methods. Dyes are permanent (and so will be almost impossible to remove) and are sold in water soluble as well as solvent-based formulas.
Shown above and below are sections of colored concrete flooring in the Hacienda Las Trancas, Dolores Hidalgo, Guanajuato, Mexico. This floor was constructed in 1932 and remains in superb condition (like the author) for its age.
Concrete stains: usually an concrete coloring process that uses an acid-based coloring agent that works by chemical reaction with the CaOH (Calcium hydroxide) in the concrete. Using an acid stain to add color to concrete can give any of several color ranges such as the examples shown here.
Concrete paints: paints (including epoxy paints) formulated to bond well with concrete surfaces, imparting a hard traffic-resistant surface.
Surface polishing: concrete may also be left in its natural color and color variations, polished to a hard finish, possibly coated with a clear sealant with no coloring agents applied.
Concrete sealers: indoor concrete floors as well as outdoor concrete floors that have been stained or colored are usually protected using one of several sealants.
Indoor concrete surface sealants include
Epoxy sealants or coatings
Urethane sealants or coatings
Exterior concrete surface sealants include
Acrylic sealants (recommended as they don't trap moisture below the coating), requires re-coating periodically, as often as every two years
Watch out: be sure to consult your concrete coloring agent, stain, or dye manufacturer to assure that the sealant you select is recommended as compatible with the concrete coloring agent you used. Also be sure the surface has adequately cured, dried, and has been cleaned before applying any stain or sealant product.
Watch out: several sources we reviewed including attributed to SolCrete (below) warn that rubber-backed carpet padding or throw rugs may trap moisture, leaving a white stain on the sealed floor.
Failures & Disappointments in Concrete Stain Finishes
Below the concrete floor was "stained" using an acid treatment. The light patches in the left of the photo indicate foot-traffic wear through the acid-treated concrete surface . (Rigby 2006).
Wear on a stained concrete floor will be increased by any of the following
Foot traffic, especially if there is grit tracked onto or present on the stained concrete floor surface
Wear caused by hard wheels on office chairs, library carts, trolleys, or other rolling equipment
Moisture penetrating the concrete floor from below
Moisture left atop the sealed floor
Spills of solvents or acids that damage the protective coating
Poor original concrete mix or placement or excessive water in the pour that yields a soft, spalling surface
Irregularities in the concrete surface. For example if a walked-on concrete floor surface was not smooth, if raised surface areas were left as ridges or elevated particles, the added abrasion on those surfaces is likely to wear off or through the acid washed or painted-on concrete surface leaving surrounding areas intact.
Poor surface cleaning and preparation before the concrete was treated.
White Bloom On or Under Finished Concrete Surfaces
White blooming under a clear or coloured finish on a concrete surface may be caused by application of the clear coat over moisture or by the movement of moisture through the concrete from an outside water source such as groundwater under a floor slab or from plumbing leaks.
See these diagnostic articles on mineral efflorescence that can ultimately show up on finished concrete surfaces as white discoloration below a clear or translucent coating or that may appear as a crystalline or powdery deposit on the concrete surface.
Behr Concrete Stains, Website: http://www.behr.com, Tel: USA: 800-854-0133 Ext 2; Tel Canada: 1-800-661-1591
Behr's concrete stains & dyes include solid color concrete stains, semi-transparent concrete stains, and a decorative concrete dye as well as floor sealer products.
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