Staining concrete is a very popular way to transform the appearence of new or old concrete slabs.  People are drawn to stained concrete due to the unique color combinations and application techniques that are available.  The results are limited only by the imagination of the person doing the staining.  Due to the porous nature of concrete it is in many ways the perfect canvas for topically applied color stains.  Stained concrete provides the best of both worlds… beauty and functionality. Concrete staining gives a luxurious feel that is impossible to get with any other coloring technique.  With most products it leaves behind a permanent, flake proof color.  Stained concrete can be used in an ever-expanding array of exterior and interior applications, including walkways, patios, interior floors, kitchen countertops etc. It’s an easy and economical way to improve the look of bare concrete floors.  There are currently two main types of concrete stain… Acid stain and water-based stain.

    In recent years, acid-based chemical concrete stains have risen in popularity.  They enable contractors to achieve rich earth toned color schemes, giving a one of a kind look to your concrete applications.  Concrete acid stains are generally a mixture of water, hydrochloric acid, and acid-soluble metallic salts.  They work by penetrating and reacting chemically with lime in the concrete.  After etching, acid stain allows the metallic salts to penetrate easily into the slab.  Once the chemical reaction takes place the stain becomes a permanent part of the concrete.  The chemical makeup of each concrete slab is different.  This means that different concrete slabs will take the stain in varying degrees of intensity.  For this reason it is always important to stain a small sample area in an inconspicuous spot to insure customer acceptance before proceeding with the staining project.  One downfall of chemical acid-stains is the lack of color options.  You will mostly find them in a limited array of earth tones such as browns, soft blues/greens, and terrra cottas.  If earth tones are not what you’re looking for you can always opt for using water-based stains/dyes instead.

    The main difference between acid and water-based stains is that  acid stains react to the chemicals in the concrete, whereas water based stains are closer to a coating that bonds with the concrete.  Acid stains give a translucent look, while water-based stains can be used to achieve either a translucent or opaque effect.   Since concrete floors are very porous, tiny color pigments in water-based stains absorb into the pores, requiring no toxic chemicals to produce the colors that you need. They can be polymer, acrylic, or epoxy based.  There are many advantages for going with water-based concrete stain instead of acid stain.  They are often used as a non-hazardous alternative to acid stain, while still capable of achieving the same mottled look. With water based stains you can build up color over multiple coats until you’re able to match the original sample that was approved by the customer.  The increased predictability with water based stains over acid stains is truly an asset for DIYers and contractors alike.  Another advantage of water based concrete stains is the decreased wait time between additional coats and sealing.  After only a couple of hours of drying, the surface can be sealed with a sealer of your choice.  With chemical stains, after waiting several hours for the chemical reaction to fully take place, you are required to neutralize and clean the concrete surface before applying sealer.  This greatly increases the time it takes to fully complete a decorative concrete staining project.  These stains are ideal for outdoor application due to the fact that they are non toxic and will not kill your lawn.  Also, Water based stains put you in control of your color.  With water based stains you can layer multiple colors to create an infinite amount of customized looks unavailable with acid stains.   In combination with acid and water based stains, concrete dyes can be used to make vibrant colors and accents.

    Dyes are much newer to the decorative concrete scene than traditional stains. Their ease of use, wide color variety, and vibrancy has caused a recent surge in concrete dye popularity.  Dyes work hand in hand with stains to provide color variations and treat problem areas that didn’t stain well.  Much like water based stain, concrete dyes take advantage of the porous concrete structure by absorbing into the surface.  However, the size of the color particles in dyes is much smaller than that of stains, allowing for a greater degree of  penetration and saturation while leaving less residue on the surface.  This provides a much more intense and vibrant color than stain. The downside of this is that the very fast penetration of dyes leaves little room for error during application.  Also, concrete dyes are not UV stable which means in most cases they are for indoor projects only. 

    When staining concrete, surface preparation is a key step. This is vital to insure that you get the most effective and blemish free stain possible.  First, put some water on the surface of the concrete in various location to see if it is absorbed.  If the water beads up then curing agents or sealers may be blocking absorption. These agents along with any grease, oil, paint drops, taping compounds, caulk and other possible contaminates must be removed before staining.  Clean the concrete by applying solvents and stripping agents, sanding, grinding, and scraping surface contaminates. If you choose a stripping agent that will mix with water you will have a much easier time picking up removed contaminants.  If grinding the concrete, try to avoid leaving marks as they will reflect through the colored finish.  You can achieve this by using the proper grinding head/pad and lightly touching it to the concrete while moving it in small circles until blemishes are removed.  If need be, patch the concrete using an acrylic modified, low shrinkage material that will accept stain.  Unfortunately, these patches WILL show in the finished product, and the owner should be made aware of this. The final step is to wash the concrete with water and detergent.  It’s easiest to pick up the leftover residue with a wet vacuum.  If applying water based stain or dye you may want to acid etch the concrete to improve adherence and absorption.  DO NOT acid etch the concrete when using a chemical acid based stain.  This will decrease the lime in the concrete and cause the chemical reaction to be minimal.

    There are many ways to apply stain and they often differ from manufacturer to manufacturer. For example, on new concrete applications some manufacturers say that a new slab must cure for 28 days after being poured.  Others say 14 days.  It would be difficult to go into detail about all of the application techniques suggested by all the manufacturers, so instead I will be giving you some general guidelines. One thing to consider with decorative concrete is that the sooner you apply stain after the concrete is placed the more intense the color will be.  This is true with overlays as well as new concrete slabs.  I would suggest that you ALWAYS DO A TEST SPOT in an inconspicuous place before proceeding.  Concrete stains can be very unpredictable and what you see on the color chart is not always exact. Before you get started make sure to mask off surrounding areas to avoid accidental staining. If you accidentally spray your wall you are going to have a very hard time removing the stain.  Sprayers are often used for application of concrete stains.  If you are using a chemical acid stain then you need to be sure that the sprayer is rated for acid and has no metal parts.  Acid will destroy metal parts and possibly ruin the color of your stain in the process.  Remember, additional water can be used to create different concentrations of stain. Many installers will work with a diluted stain and apply multiple coats to slowly build to the desired color.  This way you don’t get stuck with a darker color than originally planned for. When applying with a sprayer I suggest that you spray in a circular pattern going left to right and then right to left.  It’s a good idea to scrub the stain in just behind the spray using a medium-bristle brush in a circular motion. One more spray pass behind the brushing will remove the majority of unwanted brush strokes.  Doing it this way will help the stain to penetrate the concrete while leaving behind the minimal amount of brush and spray marks. 

    When using a decorative concrete chemical acid stain you will be required to perform some cleanup before applying sealer.  After the chemical reaction has taken place, these types of stains will leave a layer of residue on the surface of the concrete.  This residue must be neutralized and cleaned off.  Typically a scrubbing machine and water mixed with detergent is used.  Add baking soda to the mix to effectively neutralize the remaining acid.  Scrub with a buffing machine and pick up the residue with a wet vacuum.  Appropriate cleaning is a must if you want your sealer to properly adhere to the surface.

    Once you’ve put down your stain and you’ve done the proper cleanup it’s time to seal your concrete.  Sealers provide long term protection as well as color enhancement. For exterior applications you will most likely want to use an acrylic sealer to allow moisture in the slab to escape.  When used outdoors a solvent based acrylic sealer will generally perform better than water based.  You can use a silicone based sealer if you are trying to avoid a wet or shiny look.  For interior applications the primary types of sealers are acrylics, urethanes, and epoxies. Acrylics are UV stable, inexpensive, and easy to apply, but they are soft and require the most maintenance.  These provide a glossy look that really enhances the appearance of colored finishes.  As previously stated, there are both solvent-based and water-based acrylic sealers.  When applying indoors some contractors prefer to put down one coat of solvent based acrylic sealer followed by a topcoat application of water based acrylic.  This makes maintenance as easy as applying another coat of water-based acrylic sealer or wax once every 2-3 years.  Epoxy based sealers are much harder than acrylics.  Water based epoxies bond well to concrete and provide a clear finish.  Unlike acrylics, epoxies are non-porous and will not allow moisture to escape.  These factors make epoxy sealers the best choice for concrete countertops and food preparation areas.  They are not UV resistant so they cannot be used outside.  Also, reapplying epoxy sealers requires much more elaborate preparation than acrylics.  Urethane sealers provide the most scratch resistant surface of the three.  Unfortunately they are also the most costly.  Urethane sealers have trouble bonding to concrete and must be applied over water-based epoxy applications.  They are not UV-stable, and reapplication is expensive.