Here's my summary/how to on concrete floors.



Rent a terrazo grinder, mine ran about 70 for the machine and 60 for three blades. Clear the garage because it'll be out of commission for a week.



Being able to hook a hose up to the grinder is immense. The applied water whisks away the concrete dust instead of letting it be thrown into the air. Concrete dust is fearsome.

You'll know you've ground enough when the floor becomes nice an white, see right side compared to left above. The grinder will leave swirl marks that will be visible, make sure this is the look you want. Machines that hone concrete are not used on existing residental applications.

A two car garage won't take more than a couple hours, so an overnight rental is entirely reasonable. An angle grinder with a concrete disc can take care of corners if they matter to you.

The ground concrete should be sandpapery, the epoxy will make it smooth.



Notice how white the floor is when dry (and powdery). Years of wear had both smoothed and stained the concrete. My best guess is that doing the acid without grinding would mute the colors and leave artifacts where there were stains - could be good or bad. I would also worry about epoxy quickly delaminating from a poorly-prepared surface.

Buy the chemicals. I picked up five gallons of acid for what I generously estimated to be 1000 square feet of concrete (including the inside of the house). When all was said and done I had only used half.

The shop had prescribed two overlayers, epoxy then urethane. In retrospect I might have just tried a couple layers of urethane, but more on epoxy troubles later. The square feet/gallon estimates here were pretty good.



Power wash and/or brush away the concrete dust and whatever else may have accumulated on the floor, the acid should be applied to a wet surface so don't worry about planning for any drying time.

I sealed up a crack knowing full well it wouldn't be hidden by the chemicals. Some might count this as a bonus for the distressed look. I hear there are elegant methods for blending patch jobs into the process, but I didn't take this route.



Applying the acid stain is best at night since you can wet the whole floor and not have to worry about it drying before you're done. Also, the acid works as long as it's wet, so the longer it takes to evaporate, the better.

Pump spray acid on a portion of the wet concrete and quickly brush it in. This is crucial and in the end you'll see any areas that weren't brushed. Then apply a top layer of the stain to eliminate brush marks and create some natural variation. Generally the mistiest setting works best here, if you streamed your name into the job it would stay.



The instructions advise removal of excess acid. I did not, since it would require retracing my steps and then spraying more on to cover my tracks. Kind of defeats the purpose. You'll see a layer of oil float to the top of the wet stain but this will just dry on top of everything and it all has to be washed later.



You're supposed to wait at least six hours, it's easiest just to sleep on it - not literally - and the fumes aren't bad so you don't have to worry about waking up dead.



When the acid stain dries it will leave a powdery residue. This should be neutralized with ammonia and removed.



The clean and wet floor will look like a marble, though notice some haze where there's just water sitting on top of the concrete. I can't explain it, though some of it's the fact that I don't have a polarizer for this lens.



The next step is to apply the epoxy. The instructions say the floor should be clean, but it must also be dry. Very dry. Even though the epoxy is water-based. And water should not contact the floor in any amount for several days, even though the urethane is water-based.

The epoxy goes on pretty easily with a sturdy roller on the end of a sturdy pole - it's much tackier than paint so the entire mechanism bears significantly more stress. A thin layer is best, I found success going over each spot once with lots of muscle, then very lightly to pick up excess and even it out. Any globs or thick areas will haze and that's quite bad.

I'd recommend against a second coat, but stay on the long side of the prescribed recoat time.



The epoxy goes on white, it'll dry clear.



The next layer is urethane. In the image above you'll notice the lamination where the epoxy has been put down, and that the colors of the stain are brought more to life. On the right you'll see the wet urethane.

The urethane is as sticky as the epoxy, but it goes on easier because it's thinner and the already-coated floor isn't so porous. It rolls on just like the epoxy. This is the chemical that gives stained floors their shine, though a satin version is also available.



The urethane dries pretty quickly, but has a longer cure time according to the spec sheet.



There's the white haze again, called blushing when referring to epoxy. I'm not sure what to make of it, I might point my finger at the epoxy, but it seemed to also be there when water was sitting on the unlaminated concrete.



Maybe the blushing will go away with the cure, maybe it'll be covered in road dust before then. It's local to some areas and depends greatly on how the light strikes it.
Other than that, I declare success.

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