Concrete Staining Tutorial
This is a fairly extensive concrete staining tutorial which walks you through our staining process. We think an educated customer creates the best outcome for all our staining projects. This particular tutorial is directed at interior acid staining but almost all of the principals are the same for exterior work. Let’s dive in!
Please keep in mind that this is just a general informational tutorial and consequently does not cover every aspect of the concrete staining process or even describe all the details and processes needed to do it. We are just trying to give you an idea of the steps involved.
How to tell if your floor can be acid stained
The most important decision we make before starting an acid staining project is determining if a particular concrete floor is a good candidate. By this we mean will the final result be beautiful or a disaster?
We always know that decorative concrete is an imperfect process and there will always be some areas of the floor that are less than ideal, but that’s what gives it personality; even so, we don’t want the final result to look ugly.
The first thing I ask my clients is “what’s on the floor now?” The answer will tell me whether we can do a direct acid stain on the concrete or if we first need to apply a microfinish overlay (a thin, smooth coat of concrete that resurfaces the floor) to cover up the defects before the acid staining process. For exterior floors a resurfacing skim coat is the best solution. The biggest difference between the two processes is that the microfinish leaves a smooth finish that is best for interiors while the skim coat has a grittier texture that works best for exteriors.
Generally, these are the questions I ask:
• Is the project new construction or a remodel?
• What’s on the floor now? Is there tile, linoleum, wood, carpet or laminate?
• If there’s carpet on the floor, was the carpet underpad (the foam under carpet that gives it its bounce) glued to the concrete floor?
• If the project is an exterior project – is there oil, grease, paint, battery acid spills, or other contaminants on the concrete?
The ideal candidates for direct acid staining are usually new construction projects (where nothing has been put on the floor and it has been kept clean) and exterior projects that have been kept clean. These are the easiest staining projects to tackle as the floors are generally clean to start with.
Remodels are harder as any imperfections left behind from the previous floor covering (tile, linoleum, wood, carpet, laminate, etc.) will show up to some degree in the final stained floor.
Our biggest concerns are things that leave a permanent stain on the floor. In the case of remodels, if the carpet underpad was glued to the floor, that’s almost a guaranteed show stopper. Why? When the carpet installers lay down and glue the underpad they do it haphazardly in different parts of the floor, a little here, some more there, and it’s usually just thin wiggles that look like snakes.
Those thin, random lines of glue tend to wick into the concrete and they are a bugger to get out. They are the nemesis of any concrete staining project. You can hit them with degreaser, chemical strippers, sand them, sometimes even grind them and they may still show up in the final acid stained floor.
This is because the wicked glue often lies just below the surface (and sometimes much deeper depending on how porous the concrete is), and when the acid stain is sprayed, it just can’t react as well with that glue encrusted concrete as the bare stuff right next to it; so the glue lines end up being highlighted.
Sometimes it works out. Below is a floor after the carpet was pulled up; you can see the “wiggles” from the carpet glue and some spray painted instructions. In the next picture you can see they were successfully removed as they don’t show up in the final acid stained and sealed floor.
Before - Visible glue lines
After - Glues lines removed
The next pictures show what happens when it doesn’t all come up. Not the prettiest sight. That’s why cleaning this carpet glue can be quite a challenge for any staining project and why we often recommend the microfinish overlay instead of a direct acid stain when there is carpet glue involved.
Before - Visible glue lines
After - Glues lines still visible in finished floor
Concrete Staining Tip #1
So how do you find out if the underpad was glued? Simple, go to a corner of a room, lift up and peel back the carpet two or three feet away from the tack strips that hold it in place (those thin wood boards with nails sticking up). Then grab the underpad and try to pull it back, if it comes smoothly off the concrete – not glued; if it doesn’t move at all, or tries to tear while you’re pulling it – glued.
Don’t pull too much carpet back or you’ll have trouble returning it to its original position. Please keep in mind that not seeing glue in one spot doesn’t mean there isn’t any somewhere else. The best practice is to lift up the carpet in several areas to make sure.
We rarely do a direct acid stain on concrete floors that have had the carpet underpad glued down for the simple reason that we can’t guarantee the lines won’t show up. I don’t like seeing a beautiful acid stained floor that has lines running haphazardly through it then trying to tell the customer how “it doesn’t look so bad”. Not the best outcome after so much work is done.
Another thing about carpet – it’s usually held in place by a tack strip that runs around the perimeter of the room. Basically these are wood strips with nails sticking out of one side that the carpet is stretched on to while the other side has large concrete nails.
Those strips are hammered into the floor and when it’s time to remove them, they take a little chunk of concrete with them about the size of a dime every four to six inches around the perimeter of the room.
Those holes can be patched with a little concrete resurfacer, however the concrete stain will react differently with these patches compared to the rest of the floor and so they stand out (a little less if our client chooses a dark color for the floor but still visible).
In the following pictures you can see the average size of the hole left behind after pulling up the tack strips (dime sized) and how the floor looks after staining without first patching it. The concrete stain pools in these spots and darkens them.
Carpet tack strip
Hole left behind after removing strip
Holes not patched and stained
In the next pictures you can see after we patch and then stain. We need to be careful and gently remove the strips, just tearing them out will create larger holes that will really stand out.
Patched tack strip holes
Patched tack strip holes after staining
Remodels that have tile, linoleum, wood, and laminate can also be tricky for any concrete staining project. All of these tend to leave a trace behind after removing them, some more than others.
Linoleum always leaves some glue behind but this isn’t too bad, we often get most of the glue off and since it was applied in a uniform coat what’s left behind is usually in small, scattered patches that work very well with an acid stain motif.
By the way, we don’t expect to get all the glue off the floor because no concrete is perfectly flat. We use buffers and razor knives to pull up the bulk of the material but because the concrete floor has high and low spots, pits, and other variations, we can never get it all up.
Tile, wood, and laminate are in a category by themselves. They can be quite difficult to remove and tend to leave behind a keepsake that we call a “ghost image”.
This image is burned into the floor through a process called vapor deposition that will be still be visible after we’ve completed the staining project. Vapor deposition is a technical term, but the explanation is simple; let’s take a look at ceramic tile.
Tile is almost impermeable, i.e., it doesn’t allow moisture to pass through; on the other hand, concrete is porous. Your concrete floor is constantly “breathing”, i.e., water vapor is passing from the ground surrounding your foundation into the floor and eventually into your home.
This moisture is always coming in but never enough (unless you have a broken water pipe) to actually be visible or pool on the floor. It’s just a vapor. As this moisture enters the home and smacks into an impermeable object in its way (ceramic tile), it looks for the path of least resistance, which are the grout lines.
At the same time, this moisture is pulling small amounts of minerals out of the concrete with it that, as the water evaporates into your home, get left behind on the floor. After a few years these minerals create a “ghost image” of the tiles that show you exactly where the grout lines were.
This also happens with VCT (vinyl composite tile-those small, glue down linoleum squares), wood, and laminate planks.
Since concrete staining is translucent if you see any pattern in the floor before staining, it will still show up afterwards. The acid stain reacts with the minerals in the concrete, highlighting these “ghost images”. Here are some before and after pictures showing tile ghost images. You can clearly see where the tiles used to be and how they look after it was acid stained. If we suspect that there will be ghost images, going with a darker stain is usually the best way to help blend them in.
This is what the floor looks like after staining. In this case, I think they came out looking nice but I realize it’s not for everybody, it all depends on your expectations. You can also see where there had been carpet tack strips. Regardless, if you are undertaking a direct concrete staining project and had tile, you can almost guarantee it will show up in the final floor finish. This is why we recommend the microfinish overlay for most interior remodeling projects or a skim coat for exterior projects.
Here is a video from our youtube channel that really highlights what it means to stain a floor that is in a “less than ideal” condition.
Exterior concrete staining projects like driveways, sidewalks, and patios are always easier than interior ones; ultimately the decision to do a direct stain depends on what condition the floor is in. If the concrete has battery acid, oil, or other contaminants spilled on it, then keep in mind that these will show up in the final finish.
Painted surfaces can still be acid stained, but the paint will have to be removed (usually by sanding or chemically stripping it off) and small patches of it may remain. When I see an exterior concrete floor that has been painted, or stained from battery acid or oil, the first thought that pops into my head is a skim coat overlay (a thin, grainy coating of concrete that resurfaces the floor).
This is almost the same thing as the microfinish overlay, but for exterior floors. By skim coating the floor we start with a fresh surface and don’t have to make compromises.
One last point is that until we actually pull everything off the concrete, whether interior or exterior we don’t know what shape it’s in. Some things are more of a concern (patches) than others (cracks).
Patches are relatively uncommon, most contractors build good foundations and know how to finish them off so this does not normally come up but when they do it can be a big deal.
We find patches when mistakes were made during the original concrete pour; someone forgot to run an electrical line to the island cabinet in the kitchen or they didn’t level the living room area as well as they should have. The forgotten electrical line requires cutting a trough in the concrete, putting down the new line then filling it with new concrete while the leveling problem requires floating a thin coat of concrete (almost the same thing we do with the microfinish overlay) to even things out.
Of course, since both have a different type of concrete than that of the original pour, concrete staining it will create an obvious difference in the final floor finish.
Here are a slew of pictures showing acid stained floors that have been patched or repaired. This first group of three pictures are from plumbing repairs where they came in, tore out the concrete to fix some pipes, then repoured the area. We sprayed the acid stain over the entire area, but it created a completely different color over the patches.
Here we have a series of projects showing what happens to the color when different things are done to the floor.
In the first we have a brown acid stained floor where we ground the area around the electrical outlet in the floor, After staining it had a different color.
Next you can see where even if you pour all of the concrete at the same time, different finishes will affect the color. One part of this floor was finished with a hard trowel (smooth finish) while the other was broom finished (textured finish). The stain reacts differently and consequently creates color shifts.
Lastly, we had to place a microfinish overlay patch to repair some wavy concrete inside of a veterinary office and then applied a concrete stain. We got close to the same color in this one but not exactly seamless as you can see. With any concrete staining project you have to accept that these patches, repairs, or touchups will look different, the only way to make it all look the same is to apply a microfinish overlay to the entire floor.
All these issues are similarly true for exterior concrete. Say you had some lovely flower pots sitting on your back patio for some years. You diligently water your plants and one day decide you want to acid stain your patio. When we move those pots, clean the floor and stain, lo and behold, there is a ring burned into the floor where the excess water drained out from the flower pot. It won’t go away unless we first apply a skim coat overlay to bury it under a new coating of concrete.
Another thing we often see are cracks which are very common and in spite of what you may think, one of the last things I worry about. Cracks in concrete are very normal, there’s a saying we often use “there’s two types of concrete: cracked and going to crack.” We like to think it adds personality to a floor. Don’t sweat it; all reputable builders adequately reinforce their concrete floors so the cracks that occasionally show up don’t normally turn into major issues.
Cracks in stained concrete floors are very common as you can see in the pictures below. With any concrete staining project don’t worry when you come across cracks, they give the floor “panache”.
How we prepare the area for acid staining
Before we start any staining project, proper safety equipment is required! Safety glasses are an absolute must; there are a lot of liquids and other materials that can get into the eyes.
Disposable latex or vinyl gloves are a good idea, proper footwear, an activated charcoal respirator (not a dust mask), and a fire extinguisher are always necessary. We work with acid stains, bases, flammable liquids, razor knives, etc.; we just use common sense for a lot of these things.
If you’re ok with seeing some imperfections in the concrete floor (assuming it’s a remodel) and want to do a direct acid stain then we need to get the area properly cleaned and ready for staining.
Above all when we clean the floor we avoid using muriatic acid or some type of concrete cleaner/etcher! This is the last way you want wash a floor that is to be acid stained. The acid cleaner/etcher will clean the concrete all right, but at the expense of making it almost impossible to stain and/or creating very inconsistent results. This is because the cleaning/etching fluid reacts out the same chemicals in the concrete that the acid stain needs to color it.
The best way to clean the floor is with a concrete degreaser that does not leave a residue behind. I often use TSP (Tri Sodium Phosphate), which is a common mild concrete cleaner. That isn’t the name of the product, just its active ingredient; there are many different brands available.
TSP will not react with the floor in any way that will hurt the acid staining process and will help pull dirt and other contaminants out of the concrete.
We mix it at the recommended dosage with hot water, pour it on the floor and let it soak for a while. A lot of the stuff we find on the floors is water soluble like drywall texture, drywall mud, and other contaminants. A little hot water with TSP will loosen it up and make it easier to remove. For interiors, which normally have a smooth floor, we use a 17″ buffing machine with a black pad.
I really can’t see how to clean a large area without one; maybe a stiff bristle broom, a razor knife, and a strong back. It takes some practice to use a buffer but it really helps. The black pad is perfect for the job, just abrasive enough to get the crud out but not so much so that it scratches the concrete. We rarely use TSP for exteriors, (unless there’s oil) usually power washing is the tool of choice. We never use a buffer on exterior concrete because it’s generally so rough that it will tear the black pad to bits in minutes.
Concrete Staining Tip #2
Just a quick note on power washing. They’ve gotten so cheap anybody can buy them but you need to be careful using them. It’s easy to damage the concrete floor if you use a tip that concentrates the water flow into a very narrow stream (you can carve your name in concrete with some of these) or if you use the right tip but put it too close to the surface. The higher powered models will strip the “cream coat” right off the concrete, exposing the sand, stone, and cement mixture that makes up the floor. You can still acid stain the floor without any problems, but that “cream coat” is what gives the floor personality as it has variations in color, density, and texture. Stripping it away creates a very consistent looking floor that will take acid stain but looks a lot more boring.
Often, especially around the bottom of the walls in a room, we find paint or drywall texture overspray. There is no easy way of removing this if the buffer doesn’t pull it up. We have to get on your hands and knees and take a razor scraper to it. It’s a lot of work but we can’t get lazy here; anything left behind will show up later.
Of course, we rarely find concrete floors that just need a light cleaning in a remodel. Normally they’re coated with paint, pipe dope, glue, varnish, and just plain gunk! It’s been our experience that nobody gives a hoot about the floor when they’re building the home; everybody figures you’re just going to cover it with tile, linoleum, wood, or carpet so why bother? It’s understandable, but it doesn’t make our work easier. So how do we do it?
The most common flooring we find is carpet which is the easiest to remove for the average concrete staining project. We just use a razor knife and cut the carpet into strips, roll them up and then tape them so they’re easy to handle when we dump them; same with the underpad.
Now if the underpad was glued to the floor (no guarantees that the glue lines won’t show up!) then the best approach is to use a chemical stripper to remove the glue. We also use sanders and grinders to attack these but with the understanding (very clearly passed on to our customers) that it’s the choice of last resort, we cannot guarantee that the glue lines will not still be visible after we are done and that if we sand or grind the floor, those areas will look very different from the rest of the concrete.
We have to be careful as an industrial hand held grinder or sander can do a lot of damage to the floor and the user in a very short period of time if you don’t handle it correctly.
The easiest way (and least damaging to the concrete floor) to try to remove these lines so they don’t show up is using a chemical stripper. Many brands are available, we just follow the directions and keep in mind that they are very toxic (meaning they require using a respirator while applying-not a dust mask!), extremely corrosive (yes, they will also strip skin-personal experience), and not very environmentally friendly (though soy based strippers are available).
Concrete Staining Tip #3
When we use chemical strippers, we follow the instructions to the letter. Generally you brush it on in one direction (not back and forth) and allow it to sit for a while before scraping it off. We don’t ever let the stripper dry, it needs to remain moist for it to strip the glue, if it dries completely we would have to reapply it. We avoid windy days if the project is outside and make sure all fans are off inside.
We pretty much always use mechanical agitation (a buffer with a black pad or equivalent) in combination with a light coat of water to scrape the glue off. The water helps emulsify the glue and other grime in the concrete floor, allowing the buffer to get it out more effectively.
We always use a shop vac to pull this residue out of the floor immediately after buffing it. It’s the best way to get this crud off quickly before it dries because mopping it won’t get it all out.
Using a chemical stripper will cause the floor to stain differently where you applied it. (Tip provided directly from the “School of Hard Knocks”). By using a chemical stripper and scraping or buffing the glue off the concrete you are simultaneously spreading a thin layer of this contaminant all over. It’s thin enough that acid stain will penetrate and stain the floor but the acid stain color changes a little bit in this area.
Using a shop vac helps by pulling as much of this crud out of the floor but does not eliminate the possibility! At the end of the day, we sometimes find that instead of a sharply defined line running through the floor, we have a wide, hazy cloud where the original one was. Yep, there is no perfect solution to removing carpet glue lines and absolutely no guarantees, but at least this makes them less obvious.
If we are removing linoleum glue then we do the entire area, if we applied the stripper to parts of the floor and not the entire area there will be very visible color differences.
Did we mention we hate carpet glue lines? They are almost impossible to get out in any concrete staining project.
That’s why we pretty much always go with a microfinish overlay in these cases. It’s hard to spend two days cleaning a concrete floor, another two or three staining, sealing, and waxing to then see lines or “clouds” all over the place.
And of course the lines always appear on the last day after we have sealed the floor which enhances the acid stain color. Oh yeah, and getting paid after these appear can be hard, even when we forewarn the customer that they can show up.
Usually if we have to do a direct acid stain on this type of floors we will do some combination of chemical stripper and sanding to “blend in” these lines, always with the understanding that there will be visible differences in the concrete floor’s appearance.
Don’t get me wrong, it can be done, it’s just that you don’t know what you’ll get until after the acid stain hits the floor and you’ve sealed it. Since we’ve mentioned the microfinish overlay process a couple of times, here’s a video showing how it’s applied.
A quick footnote here, we aren’t big fans of chemical strippers. It’s stinky, corrosive, expensive stuff – so we do try to avoid them as much as possible. When we use them it’s usually to remove small problem areas such as spray paint or permanent marker ink that has soaked into the concrete.
If the paint or marker ink doesn’t come out with the stripper then we try soaking a small rag with lacquer thinner and placing it over the affected area for 10 minutes or so to help pull it up. Sometimes we have to repeat it a few times.
In lieu of strippers (the chemical kind) we often use special scraper blades that we can mount on our buffers. These have carbide blades that scrape the surface of the concrete and can often remove just as much glue as the strippers but without the mess. You can see it in action in the video above
Concrete Staining Tip #4
To remove linoleum we always cut the floor first using razor knives into long strips about six or eight inches wide (angling the knife so as to not cut directly into the concrete) then come back with floor scrapers, push the tip underneath one of the strips and then follow it, peeling it up as we go. If you don’t cut it then it’s trying to lift an entire glued down sheet of linoleum and either you’ll tear it as you’re lifting it or you just won’t have the strength to do it. It’s just easier to remove it one section at a time.
If the concrete staining project involves glued down wood or laminate, we try cutting the floor into strips using a circular saw. We make darn sure to adjust the cutting depth of the blade before we start to just a little less than the thickness of the boards and use a carbide tipped saw blade knowing that once in a while it’s going to knick the concrete underneath.
Once we’ve cut the wood laminate into strips we break out our chipper hammers (electric demolition hammers that have a chisel on one end) and gently ease them under the wood and start peeling up the material. That way it peels it up much easier and faster than a floor scraper. Let me tell you, there is quite a difference between using the machine and doing it by hand.
Now for the humdinger of them all – ceramic tile. This is the hardest floor to remove for the average concrete staining project.
No real easy way to do this, we pretty much always use chipper hammers. It’s hard, dusty, dirty work. Every time that hammers hits the tile or the thinset underneath it there is a small puff of dust created that will settle everywhere.
We need to be careful with the hammers; it’s very easy to dig and chip up the concrete and the damage will be very visible in the final finished floor. Sometimes the tiles will come up whole, other times they will just shatter; we try to get them up whole as there are a lot less pieces to handle.
We always use gloves and safety goggles when we do this work because the pieces of tile can fly through the air and they are very, very sharp (I can also personally attest to this). We also install carpet blowers (large industrial fans) at any available opening to the outside to help blow some of this dust out.
Concrete Staining Tip #5
Did we mention this is dusty work? In addition to the blowers we will sometimes duct tape a vacuum hose from the shop vac to the chipper hammer so that it will also suck out the dust. We try to extend the hose as close to the chisel as possible for maximum effect. It’s a little unwieldy but we usually make it work and it definitely helps keep the dust down.
The tiles themselves aren’t the hardest part, it’s the thinset below that held them to the floor. All of that special cement needs to be cleared away and the floor smoothed as much as possible before we start the concrete staining project; anything left behind will be remain visible in the final acid stained floor.
You can shave quite a bit of it off with the chipper hammers or even a handheld chisel and hammer but it’s a lot of work. We normally will break as much of it away as possible then come in with our buffer mounted scraper blades to get the rest of it out. It leaves a much smoother floor than what we could get just using a chisel and remember, anything that gets left behind will be visible in the final acid stained floor.
Whatever procedure we use to prepare the concrete, it’s very important to make sure the floor is completely clean before moving to the acid stain step.
We always use a shop vac in wet mode for this as it will suck up the dirty water. Trying to use a mop pushes it around instead of getting it out. Any contaminants left behind will affect the concrete stain.
Now that doesn’t mean we don’t use mops, sometimes the shop vac will leave thin little lines where we’ve stopped and lifted the wand to clean another area and these will also show up in an acid stain. Damp mopping the entire area just prior to staining will even out any dust, dirt, or other contaminants so that they don’t show up as lines.
If the client wants it, then the next step is scoring (cutting a shallow groove to create a stone, diamond or tile pattern) which involves special equipment and experience; you can really mess up the job if done incorrectly and even hurt yourself if you don’t do it right.
If we are going to score the concrete floor this is the time for it. Scoring concrete requires using a diamond saw blade that lasts a lot longer while cutting concrete than traditional abrasive types of blades. We usually mount this blade into a shrouded circular saw because the cutting process generates a tremendous amount of dust. The shrouded saw has a housing that covers most of the blade and an attachment for a hose from a shop vac.
We use the saw for the majority of our long cuts then come back with a handheld 4″ angle grinder for touchups-one guy cutting and the other holding a vacuum cleaner hose right next to it.
We always have to do touchups as no concrete floor is perfectly flat and the saw’s height adjustment can’t be changed on the fly. Sure, we could lower the saw blade so that it will always cut the floor but that would create deep cuts and as any homeowner with tile knows, deep grooves in the floor accumulate dirt. We avoid this by making light, shallow cuts (no more than 1/8″ on average) and wherever there’s a dip in the concrete we come back with the handheld grinder to finish it off.
Before scoring the concrete in any acid staining project we need to know what pattern is going to be cut. Here’s a video showing some of the stuff that can be done.
The most popular patterns are tile or diamond (which is just a tile pattern set at a 45 degree angle) but as you see in the video, there are other options. We also do a lot of Texas Stars, North Stars, and custom logos all of which we can acid stain a different color from the rest of the floor.
There are a couple of design elements we take into consideration before putting down the pattern. First, consider the size of the room and the adjoining areas. I personally like large tile or diamond patterns with each tile being 24″ x 24″ or larger. I never like walking into a room that has a small 12″ or 18″ pattern scored into the concrete floor; it just looks too busy, especially in larger rooms. Bigger always looks more elegant.
Of course, you can go too big, especially when going from a room to a hallway or bathroom. If the pattern is too big then you get truncated tiles or diamonds when transitioning to smaller areas. We’ve found that 24″ works well in most cases and bump it up to 36″ whenever we can.
The first step we take when scoring a diamond or tile pattern is to pop out an 8″ wide border around the perimeter of the room with a blue chalk line. We absolutely avoid using red chalk since it often doesn’t come out, no matter how hard you scrub it! We need the border to create a start and stop point for the tile pattern as we can’t score the floor right up to the wall without actually cutting it.
Some people will score the concrete after concrete staining. I’m not a big fan of this technique for a couple of reasons. First, when you score after acid staining, the cuts are very pronounced as they are much lighter than the rest of the concrete floor.
To me, this seems to shift the focus of the floor from the acid stain to the lighter score lines. When you score first, then acid stain, the stain colors the grooves, creating a blended, softer effect. Second, any mistakes you make scoring the floor will be much more apparent if you score after acid staining. Why draw attention to mistakes if you can avoid it?
In the first picture you can see a floor that was scored after acid staining. Doing it after really highlights the score lines. Next is a concrete floor that we acid stained each scored tile an alternating color. The next couple of pictures are some different scoring designs we can do, from a diamond at the vertices of some of the tiles to very large tile patterns. The last two are a Star of Texas and a North Star.
Almost there! One more important step before concrete staining. We need to protect anything that may get sprayed on-both interior and exterior jobs.
We use a combination of blue painter’s tape and pre-taped plastic drop cloth for this job. It needs to be meticulously applied; if we try to shortcut this step in the acid staining project we’ll damage any adjacent walls, stonework, doors, and flooring.
We do this in two steps; the first is to follow the lower edge of the trim running around the room with the blue tape. It needs to completely cover the trim because anything that shows will get sprayed with acid stain. Doors need to be wrapped on both sides, any other flooring that butts up to the area to be stained need to be taped over.
We always say it’s better to err on the side of caution here. We don’t want to be in the middle of acid staining the concrete and realize that we didn’t protect the other side of the door or forgot to tape up part of the wall. It’s the same procedure for exterior concrete, we use red duct tape instead of the blue as long as it’s not on a painted surface or it will pull the paint right off when it’s time to remove it.
After applying the tape, we run the pretaped plastic drop cloth over the tape along the wall. This is a plastic film that protects everything from overspray. We make sure to check for any holes in the film as it’ll allow stain to get through and that will bring a world of pain to the concrete staining project. Now we’re ready to mix the acid stain!
How to mix acid stain
What brand of acid stain do we choose for our concrete staining? There are many available, ranging from Scofield, Brickform, and Kemiko, among others. Some stores even sell their “house” version which we have found actually works pretty well.
Between you and me, I think they make all the acid stains in one place and then just slap a different label on them as they go down the line. I’ve done side by side tests of one brand’s “X” next to another’s “Y” and can’t tell the difference between them, so as far as I’m concerned, we normally buy the most economical one there is and use it.
We know the colors will never match their sample cards because acid staining is a reactive process and every concrete floor is different from the next. That’s why we always spray a sample of several colors on the floor and let the client decide which one they like. Sometimes we’ll buy sample kits that have six to eight small bottles of different acid stain colors so that we don’t have to buy a gallon of each for our samples.
Concrete Staining Tip #6
So what color to choose? Obviously this depends on your tastes but some things to consider are the furnishings in the room, how much light there is, and what the room(s) are going to be used for. If you are going for a formal look, darker colors are more appropriate; however keep in mind that it can suck the light out of the room, especially at night. Lighter colors are actually easier to keep looking clean; I often use the analogy of a black and gray car after a rainstorm. You can see every dried raindrop on a black car while the gray one hides them better. Footprints and other stuff that gets tracked in show up more on dark floors than light ones; but if you are trying to cover up floor defects, then darker colors are better.
One common acid staining mistake is to apply the acid stain at full strength. We almost never do because it can create a very dark concrete floor; we usually dilute it with water. By diluting the acid we reduce the material cost and it’s easier to control how dark it gets.
We normally dilute the acid at a ratio of one part acid to one or two parts water, i.e., 1:1 or 1:2 and even 1:4. The more diluted it is, the lighter the color. We always apply two coats, making sure we have 100% coverage of the concrete floor.
We only use plastic sprayers for applying concrete stain for the simple reason that a sprayer with any metal parts in it will instantly react with the acid stain, literally dissolving away in a show of smoke and heat.
This includes the all plastic sprayers that have a metal tip; I’ve seen them get hot enough to burn you on contact. Though our sprayers are professional grade, in a pinch, we will use a good grade pump up sprayer that you can pick up at a Home Depot or Lowe’s. We always use sprayers that have VITON seals as these are more resistant to acid stains.
After mixing the acid stain and water together (obviously in a plastic, not metal, container) we fill up the sprayer and go to work. Just like painting, you want to back out of the area you are working in.
We start in a corner and apply it in a figure eight pattern, always overlapping the spray on itself. The most important thing to avoid is pooling the acid, we apply it sufficiently heavy to wet the concrete floor but not flood it.
We carefully walk out of the area, avoiding stepping on the acid. If you step in it then step on the unstained concrete, you will burn a footprint right on the floor and it will not go away, even if you spray more acid on it! We actually use spiked shoes, kind of like soccer or golf shoes, so that if we accidently step in it then the footprint is a lot less obvious, just a series of points that can be easily blended in.
Now comes the hardest part in concrete staining – waiting. It’s a reactive process and so the longer it has to work on the concrete the darker it becomes.
We normally have to wait two to four hours after spraying the first coat; first to see some color on the floor and second to allow it to dry. Walking on dried acid stain doesn’t usually leave footprints, we just make sure to avoid any areas that have a “sheen” on it because they are still wet.
We then apply the second coat of acid stain all over, making sure to spray any areas we missed during the first pass using the same figure eight pattern. Normally we let the second pass react for just a couple of hours before we neutralize it.
Neutralizing the acid stain is necessary to stop the reaction process. If we don’t do this, the acid stain will progressively get darker. By neutralizing we stop it, “locking” in the color as it is at that moment.
Concrete Staining Tip #7
An acid stained concrete floor has a completely different color when it’s wet compared to when it’s dry; which is the right color? Always look at the color when it’s wet. Though it’s not going to be exactly the same color after sealing it, the color is much truer to the final result than when it’s dry.
After we have neutralized the floor, we’ll sometimes apply a small amount of water to the acid stained floor in a corner area with a damp paper towel to get an idea of the color, we don’t spray a bunch of water on an area and let it dry; the acid stain may continue to react for a longer time in the wet area and leave a shadow behind.
With acid staining it’s always baby steps. Don’t do anything to one area of your staining project that you are not doing all over or it may show up in the final finish. We don’t change our spray technique in the middle of the job, the amount applied, or any other variable since acid staining is unforgiving! We just go slow, plan out how we are going to apply the acid stain and relax, we know the color will never be exactly what was expected but it will still look beautiful.
We neutralize the same way we applied the acid stain, by spraying the solution over the floor. This solution is usually an ammonia and water mix at a 1:1 ratio.
The ammonia can be purchased from any big box store, it’s the same stuff used to clean floors or windows. Ammonia is a “base” while the stain is obviously an “acid”, so spraying the ammonia on the acid neutralizes it. This happens very quickly, usually in less than five minutes.
One caveat, the smell is pretty strong and ammonia can damage lungs if breathed in a high enough concentration. We always use activated carbon respirators (not dust masks!) specifically tailored for ammonia fumes to protect ourselves during this step and make sure the area is well ventilated.
After about five minutes after spraying the ammonia-water mixture on the concrete floor we start cleaning the residue that is a byproduct of the acid staining and neutralization process. This is usually a thin, sticky, film that coats the concrete.
We remove it by passing a fine bristled push broom over the concrete floor, add a little clean water, and a shop vac. We sweep the floor softly with the broom all the while adding a little water to help emulsify it. We immediately suck the residue from the floor before it dries using the shop vac.
We don’t try to mop up this sludge as it just pushes the sludge around instead of getting it out of the concrete pores like vacuuming. An added plus during this step is that we get a good idea of the final floor color which we can while it’s still wet. We are also very careful where we dump this residue/water mix, it will stain any concrete surface (as in patios, sidewalks, driveways, etc.) if dumped or dripped on it.
Sealing acid stained floors
We’re almost done! Before sealing the concrete floor we need to be sure it’s completely dry. If there is even a little bit of moisture in the floor before sealing with a solvent based sealer, it will leave a white haze which can only be repaired by stripping it off and reapplying it. The best way to verify this is by putting blue painters tape on the floor. If the concrete is dry you will have to peel it off, if it’s wet it won’t stick to the surface.
Acid stained floor prior to sealing
Acid stained floor after 1st coat of sealer
UPDATE: A few years back we’ve made the switch from flammable solvent based acrylic sealers to much safer water based polyurethanes for interior areas. Polyurethanes are safer to apply, twice as durable as an acrylic sealer, and don’t leave a lingering odor like the solvent based ones do (smell can last up to two days inside). They are much more expensive than the acrylics, require mixing in the correct proportions, and generally have to be rolled on instead of sprayed so they are harder to apply. A lot of contractors still use the solvent based acrylics as they are cheaper and easier and we still do for exterior areas so the following information is useful but all safety precautions must be followed as well as a good dose of common sense, we don’t recommend using a solvent based acrylic sealer in interior areas at all.
Though there are many different types of sealers available we almost always use a concrete solvent based sealer on exterior floors a couple of reasons.
First, solvent based sealers (crystal clear transparent in appearance and give off a strong odor) will deepen and add “pop” to an acid stained concrete floor as opposed to say, a water based sealer (usually a milky white color and low odor).
Second, solvent based sealers dry quickly and create a very durable finish. A few negatives is that the floor must be completely dry before applying the sealer, the material is flammable, and you MUST use an activated charcoal respirator (not a dusk mask!) tailored for solvents as the fumes from the application process are very strong.
First let’s go over a couple of points regarding safety, especially concerning solvent based sealers. These are highly flammable so we always check to see if there are no ignition sources in the area we are doing.
We also check our pump up sprayers every time before we start, especially when using solvent based sealers. These are hard on pump up sprayers and we only use those that have VITON seals as these are more resistant to solvents. We don’t use a bargain sprayer, this is asking for trouble.
I personally know some contractors who have had the hoses or other parts of these sprayers unexpectedly fail on them resulting in sealer spraying uncontrollably all over walls, ceilings, themselves, and of course the concrete floor.
The repair bills far exceeded the cost of the job and sealer will burn when it gets in your eyes or skin. Accidents happen, and they can happen to the best of us, but we always try to avoid problems by inspecting our equipment and keeping an eye on it while we work, bleeding off the pressure when we are not using them, and not storing sealer in them for extended periods of time.
Applying 2nd sealer coat to acid stained pool deck
Continuing with sealer application in figure eight pattern
We almost always spray the sealer on. Yes, it can be rolled but it requires a fine touch to do it correctly. Solvent based sealers are not like paint; they dry very quickly when you are rolling or spraying them on and it’s easy to “overwork” them.
If we do roll it, we go over the concrete floor just once or twice with the roller and always maintaining a wet edge. We have to work very fast as that edge doesn’t stay wet for long and if it dries, you will clearly see lines all over the floor that are hard to repair.
Take our word for it, spraying the sealer down creates a more uniform finish and you don’t want to make a mistake this late in the game and ruin the entire job. Oh yeah, and spraying is so much faster than rolling; at least three to four times faster.
Most concrete sealers come premixed, ready to be applied so it’s not necessary or prudent to dilute them any more. We always spray at least two coats on the floor and apply it the same way that we do an acid stain, in figure eight patterns.
Light coats are better than heavy ones; we don’t try to saturate the floor, the sealer will flow a little to fill in areas and what isn’t covered on the first pass will get taken care of in the second one. Most concrete floors only require two passes to completely seal them, however some are more porous and require a third pass.
We can usually tell by looking at how glossy the floor is; less glossy areas need another light application of sealer. Each coat dries quickly (usually in less than 45 minutes) depending on the ambient temperature. We always check by touching it with our hands before we walk on it. If it’s sticky, it needs to dry more, you don’t want to step on wet sealer, it will ruin your stain job and may even pull some color off the floor.
Also even if it’s not sticky, if you get on it too quickly you can leave a footprint in the sealer coat as it hasn’t hardened enough to support your weight. We always walk on it with socks on, never shoes. To reiterate, all the steps are for sealing exterior floors, we don’t recommend solvent based sealers for interiors.
We always recommend to our customers to wait a full 24 hours before placing any furniture on the floor to allow the sealer to harden because the longer it sits, the harder it gets.
Technically we are now done, we’ve applied the sealer and can remove all the tape from the walls. While we don’t do this, we do recommend you apply a wax coat on your interior (never do this on an exterior) floor prior to moving things back on. It’s a good idea as it forms a sacrificial protective barrier that helps reduce wear and tear on the floor and creates a more uniform gloss throughout the entire area.
Waxing is simple, just use a good grade rayon mop head that has a loop end and a mop bucket to wring out excess wax. As with all the other steps, thin coats are better than thick ones. Pour the wax into the mop bucket, wring it out tightly, and then apply the wax in a figure eight pattern. Wax dries very quickly, usually in less than 1/2 hour per coat; it’s always a good idea to apply two coats for even coverage.
That’s all! You can walk on the last wax coat within an hour or so in most cases. Touchups are usually done with additional wax coats which we recommend reapplying every three to six months.
Thank you for your time to read this concrete staining tutorial. We hope it helps in explaining how we apply acid stains to concrete floors. I’m not going to say it’s the only way to do this type of work; it’s just how we usually do it. If after reading this you you have any questions, contact us through the links at the bottom of the page.
Arthur Krummell 1928 – 2010
Father & Friend
Here is a final video showing how we clean, tape off, apply the concrete stain, and seal an exterior concrete patio. Enjoy!