Staining a concrete floor with fertilizer

I stained our concrete floor with fertilizer. On purpose.

Andrea and I think it looks awesome. It was also absurdly cheap and easy to do. So absurdly cheap and easy, it was harder to write this blog post than stain the floor. Okay, maybe that’s because I am actually not a fan of writing blog posts and uploading pictures, and I have more fun installing toilets than using a computer, but still… absurdly cheap and easy.

There are elaborate write-ups online but it’s pretty much mix, mop, and seal. (If you don’t seal the stain, it tends to wash off and transfer to nearby surfaces, which is no good.) The only real trick is figuring out how much fertilizer to how much water; my first attempt used far too much water (or too little fertilizer). My second attempt worked out much better. If you are the sort of person who cares a great deal about what shade of rust you want your floor to be, you should do a test patch first. I was ballsy and just went to town. In part because the concrete will take up stain at different rates so getting a uniform consistent color is pretty futile anyway.

The fertilizer I used I picked up at Ace Hardware. It cost like $12 and came in a canister. The ingredients should chiefly be ferrous sulfate. Most online tutorials mention “pure” ferrous sulfate but I couldn’t find anything locally, so I just picked up some kind of soluble chelated iron with FS as the primary ingredient. The right stuff should have a warning not to use it near concrete because it will stain. Silly warnings. (Actually you should be worried about staining stuff, just not concrete; FS turns wood black.)

Some people add coffee to the stain to make it a little more brown. I tried that on my first attempt which was pretty much obscured by my second, caffeine-free application.

Make sure you clean the snot out of the floor; any marks on the concrete will be readily apparent after staining. I used a rotary buffer with a sanding pad to remove gypsum stains, paint drips, and scuff marks. Then I swept and mopped.

Once the floor was clean I used a rag mop to apply stain but I understand a sponge mop is easier to use for more consistent results. Looking back I think I’d rather have used a sponge mop. If you don’t want stain on nearby walls, be sure to mask them well. I applied two coats of stain once I got the color I wanted, allowing the floor to dry to the touch between coats. Then I mopped the floor with water to spread the residue around a bit. You’ll have little granules of fertilizer on the floor when you’re done; just sweep them off or vacuum when dry.

If you wear wet socks you can walk across the stained area and just do a quick pass with the mop to cover the footprints.

When I was done with the stain, I rinsed my buckets in the garden around acid-loving plants. Desert soils are really alkaline, which inhibits plants’ ability to take up iron. So we add chelated iron when the leaves turn yellow. So, how many stains do you know that are good for your garden, eh?

Count on your mop head to be pretty much shot after this process. I was never able to rinse all the stain out of mine, so it is now my permanent ferrous sulfate stain applicator.

I used AFM “Mexeseal” as a sealer but you can pretty much use any concrete sealer you want. I liked Mexeseal because it doesn’t kill my brain cells or make the planet a shade more like Venus. You have to order it online or, if you are in Tucson, you can buy it locally from Originate. It went on easily, the odor was mild, and so far it seems pretty durable (if you can tell these things after two weeks). It took two coats on our floor.

So, what do you think? Have you used fertilizer to stain your floor?


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