Art by Joy Lile copyright 2006
Iron Sulphate Concrete Stain

Lawrence Lile, P.E., LEED AP

I was fascinated by Cathy Moore's story of using a cheap garden chemical as concrete stain.  You can read about her experiences here .   What attracted me was:

Photo of concrete stain
Here is an example of the results - a rich, multicolored rust or  terracotta color.  The resulting floor has many natural variations in color, reminiscent of stone.  Someone asked me "How did you get that mottled effect?"  The answer is, it is hard NOT to get a mottled, variable effect.  The photo does not capture the colors and variations in the floor, which are as fascinating as clouds. 

Although Cathy Moore gives a thorough explanation of her process, I thought a detailed, step by step approach could add to the ease of using this method for anyone who wants to try it. 

Step 1:  Why?

Concrete stain is one of the cheapest ways of creating a beautiful, durable finish in a home.  Conventional concrete stain uses acids to create colors.  A wide pallette of colors are available, but some poor fool has to don the masks and goggles, wade around in dangerous acids, breathe the fumes and deal with the waste.  Since that poor fool happens to be me, the do-it-yourselfer, I chose to try something different. 

An $11 bag of Iron Sulphate (A.K.A Ferrous Sulphate or Copperas) provided enough concrete stain for my entire house, with about 1500 square feet of finished concrete surface, with plenty left over to fertilize my tomatoes. 

You can also achieve interesting light blue colors with Copper Sulphate, also available at hardware stores.  Combining iron and copper sulphate can produce shades of brown, or add depth and highlights to the predominant color.

Step 2: Materials

You'll need 
Ferrous Sulphate

You can also try floor wax as a sealer.  Floor wax is no longer available in grocery stores, the products that are sold there are really acrylic finishes.  You can buy real floor wax here 
I chose not to use just floor wax, because I had been warned that some foods or common household chemicals might stain the floor through a layer of wax, and I wanted a more permanent finish.  Plus I was not sure it would work on this type of floor stain.  If you have any experience with this, leave a note on my blog.

Step 3: Experiment

Buy some concrete pavers with a smooth troweled finish at a local hardware store.  Arrange them out in your yard, and play with stains and finishes.  When you are done, use them in garden paths or under your hose faucet.

If your slab is already done, make test patches in closets, under your future dishwasher or in the future garage.  Try out all your materials and sealers, application methods, and so on. 

Step 4:  The Litmus Test

The type of  sealer I chose requires a certain pH, or Acidity, range in the concrete floor.  They warn that the sealer will not work well on fresh concrete, that it needs to be cured or use thier acid reducer product.  My concrete was well cured, and had a pH of 7.5, well within the proper range.  Clean a bit of the floor, wet it, push the litmus paper onto it for 30 seconds or so, then compare it to the chart on the package.  Do this in several spots for an average reading.

Step 5:  Cleaning

The floor needs to be ablsolutely clean. I spent more money cleaning the floor than I did staining it.  If you have learned how to use one, a rotary floor buffer is a great tool to use here.  If you haven't learned to use one, then you are in for a bronco ride.  Ask the rental yard to show you how to control the machine, if they can't teach you, go to another rental yard.  If you leave without knowing the trick, then you are in for a frustrating experience.  It is hard to describe, but since the rotary machine is spinning, pressure on one side sends it in a direction 90 degrees to the pressure.  If you want to go left, lift up on the handle gently.  If you want to go right, press down on the handle gently.  If you want to experience vertigo, then press the handle hard in any direction, which will also accomplish winding up the cord around you and the machine.  This will entertain your friends, but won't get the floor very clean.  You cannot force a rotary machine to go anywhere it does not want to go, you can only guide it using gentle up and down pressure.   In this aspect it is sort of like a teenage son or a horse. 

Clean the floor with mild soap, like Murphy's oil soap, and some scrapers.  I used a sheetrock knife, screwdrivers, and whatever was handy to pick up glue, spilled paint, and sheetrock mud dollops.  Anything stuck to the floor will show, so be meticulous.

Clean it again with soapy water, then with clear water.  Use a shop vac to slurp up the excess.  Be careful with the shop vac, the wheels will make dirty tracks across the floor.  I carried the shop vac when it was full of water to avoid this effect.

Ground Fault Outlet
You will be standing in 1/4" of water, operating an electrical machine.  Plug your machine into a Ground Fault Circuit Breaker.  This is the kind of outlet with a "test reset" button.  If you don't have one, get one installed.  I knew this, ignored it, and got a nasty shock from a pinhole in the extension cord insulation.  You can buy ground fault adapters at any good hardware store, if you don't have one. 

Save the rotary floor buffing pad.  It is a huge nylon scrubber with 1000 uses, and you  paid for it anyway.

Duct Tape
Step 6:  Masking

Iron Sulphate will stain wood black, even through varnish.  Mask wood carefully.  The stain mixture will run right under masking tape on the floor, so use duct tape to mask lines or at doorways where you are changing to other colors.  Duct tape will leave a sticky mess on the floor if you leave it too long, so peel off the duct tape as soon as possible.  Use plastic for masking floors, you can use masking paper on walls, which I found easier than using plastic.  If you stain the floors before the base trim goes on, you don't need to mask the walls. 

Step 7:  Ready for Stain

Mix up a batch of iron sulphate stain in a 5 gallon bucket. Use a plastic or wooden stick for stirring.  Only mix up enough to use up in an hour or two, I noticed that old concrete stain had less effect.  The formula I used is:

I thought that hard water didn't do as good a job, but if you don't have soft water available it isn't a critical. 

Keep it mixed, the iron sulphate will settle out.  Strain it through a cloth with a funnel into your garder sprayer.  Never put anything in a sprayer that hasn't been strained, they clog up fast.  Struggling to clear a clog out of the nozzle will cause you to make unsightly drips, and also emit words unbecoming of a sailor.

Have a small scrap of plywood to set your sprayer and scrub-brush on, lest you leave drips and round marks in the floor.

I applied the mixture to a dry floor, although Cathy Moore  applied it to a wet floor.  Either way works well, I found it easier to see where I had sprayed using this method.  Then I used a long handled scrub brush to really work the stain into the floor, apply a pattern, and move the stain into corners and crevaces.  You can also accomplish this with a household sponge mop, I liked the scrubbing brush because I though it left a better pattern.  Note the socks, which leave less footprints than shoes or bare feet.  When you first apply the stain, it has no color at all, but it starts to develop within 5 minutes.

Here is a photo of the results of the first coat.  Pretty ugly:

Don't panic, you haven't ruined your floor yet. 

Step 8:  Dry, then Dust, Then Wet

Allow the floor to dry.  Dust it with a dust mop. (wear a nuisance dust mask)   You aren't trying to remove any dust, just redistribute it.  Much of the stain will lay on top of the concrete at this point, in the form of iron oxide dust, and you are redistributing it, removing brush marks and footprints. 
Dust Mop

Wet the floor, using the same garden sprayer and clear water.  You can use the brush again to redistribute the stain if you want.  The more times it is wetted, the better the stain sets.  On the other hand, the more times you wet the floor, the more chances you have of producing efflorescence, which is bad. 

Step 9:  Recoat with stain

Your goal here is to recoat any areas that were missed, redistribute the stain to an even coat, and thoroughly wet the floor again.  I didn't use the brush on the second coat. 

Once it dries, you should now see a nearly even coat of terra cotta red on your floor. 

Step 10:  Put away that sprayer!

Arrgh! You missed a spot!  Resist the temptation to take out the sprayer and go over the spot again and again.  What you will accomplish will be to bring out efflorescence , which is a calcium compound that forms on the surface of concrete.  These white stains will foul up your sealer, and I think they are ugly. Efflorescence bedevils all concrete and masonry, and your project is no different.  If you have a light area, it is because the concrete won't take the stain as readily as the next area.  Don't worry, you can't control these variations, don't try too hard.  

Use a piece of the floor buffing pad you saved from step 5 to scrub the white stains, you can rub some red into them and make them not show.  A sandblaster is the only thing that will truly take them out, and I don't recommend this. 

Step 10: Sweep

You can accomplish two things by sweeping:  either redistribute the stain, or remove it.  Removing loose powder will make your floor slightly darker in the final result.  Redistributing the powder will help fill in those light areas.  Wear a nuisance dust mask.  Don't use a big push broom, it will remove too much stain.

Step 11:  Sealer

At this point you have a floor that has some stain soaked into the surface, and more on the top as a powder.  You need to seal it to protect it from stains and spills.  You can go to your local paint store and pay $35 or $45 a gallon for a toxic, smog-making, smelly sealer with 400 Gram/Liter of VOC's, and wipe out a few more of your brain cells, or you can buy a safe, non-toxic sealer from Green Building SupplyEnvirosafe, or AFM Safecoat. Conventional sealers will outgas in your house for years at low levels, and nobody knows what that will do to your health.   It's your choice - Pollute and suffer the brain-addling fumes, or not?  The cost is the same. 

I used Green Building Supply's clear gloss sealer.  I sprayed it on with a garden sprayer, then backrolled it with a paint roller.  This is a two person operation, the sealer turns pasty white if you leave it too long.  It also turns a milky color over any efflorescence, but this turns clear after it dries.  The paint roller spread the sealer into an even coat, and mixed some of the loose stain into the sealer.  I found that I had to squeeze out the roller periodically, because it would start leaving a milky partially dried sealer.  The purpose of the roller is as much to remove sealer as it is to spread it out. 

This sealer gets harder for the first 7 days.  I found that after ten minutes it was dry enough to walk on with socks, but even after one day I could remove a little of it with water and a paper towel.  After 5 days, the sealer had fully cured.  I told the workmen to walk on tarps for the first 48 hours after laying down the sealer. 

I used two coats of this type of sealer. 

The top half of this photo shows the caffeinated stain.

The bottom half shows the stain with no coffee added.  The photo does no do justice to the contrast between the two - the coffee stain looked much darker to the eye. 


Frequently asked questions:

Why not just use a colored sealer? 

I used a colored sealer in one room.  I found the results to be monochromatic, more like paint than stain.  The rich colors and variations found in the Iron Sulphate method are missing.  On the other hand, Colored sealers are a one step solution, much less complicated.  It's your floor. 

Can you sawcut the floor for a "Tiled" look?

This looks great!  I chose not to sawcut the floor, because I have radiant floor heating, and nobody had the guts to risk cutting into a pipe.  If you have a bolder concrete man, go for it!

Can you apply the floor stain dry?

I was told that some people apply the Iron Sulphate as a dry powder when the concrete is still wet.  I don't have any idea how this will come out.

When should you apply the floor stain?

You can apply the floor stain anytime between when the concrete is cured, and when you are ready to apply sealer.  I waited until the last minute, when the house was nearly complete.  Cathy Moore stained the floor right after it was poured, then let Nature and the rain set the stain.  I would apply sealer as one of the last steps in construction.  The stain will become harder and more durable if it is rained on a few times, although it also becomes less intense. 

How much time did it take?

I cleaned, stained and sealed about 1100 square feet of floor in about 5 days time, three days for cleaning, one for staining and one for sealing. 

Can I email you with lame or dumb questions?

I don't publish my email address because of spammers.  You can contact me on the Green Building Email Listserv or via my Blog.  I love to discuss anything Green, and the other knowledgable folks on the Green Building List will fill in the gaps in my knowledge.  No question is too lame or too dumb.