ok so i had my shop floor poured over 30 days ago, then had it covered in plastic for about a week after the pour while they finished the walls of the shop, uncovered it and you could see foot prints and what not in the concrete floor, so last weekend about a week after the plastic was uncovered. i muratic acid washed it the best i could, whetted down the floor with a pressure washer (mixed in a 5gallon pale of water 1gallon of muratic) then splashed it onto the concrete and used a really stiff bristled shop brush to scrub it, did the hole shop and then used a pressure washer to to rinse it, now 4 days later or so there are these big huge patches of white powder and big patches of what looks like wet cement, is this due to me not rinsing it off good enough? i even pushed all the standing water out of the shop when i was done i can get pictures
strange white powder after muratic bath?
- Thread starter malodin
- Start date
any suggestions?
i was planing on using an acrylic based concrete sealer this weekend on it, as i cannot afford the epoxy system from alpha or any other epoxy based system right now, i would love to but cannot
do i need to pressure wash it again or just let it dry for another week?
also do you think the wet looking section is from water soaking in from the ground? it has been raining the last few days but the doors have been shut, i am new to anykind of concrete floor so i dont know what to expect.
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DonL
Well-known member
The acid etched the concrete. Sweep the floor and mop it. You should be good to go.
AlphaGarage
Well-known member
The white powder you see is likely calcium carbonate. Muriatic acid (hydrochoric acid) reacts with the material in the cement and calcium carbonate is one of the residual results. A good rinse, or three, with a broom scrub followed by rinsing should get rid of most of it. And you should remove as much of it as possible before applying any coating.
Much of the remedial cleaning can be avoided if the muriatic acid isn't allowed to dry after it's done its thing. As soon as it's played out wet it down just enough to keep the floor from drying, wait a few more minutes to make sure the acid's no longer active, and then use a lot of water to rinse it off.
Muriatic acid is one of the most caustic chemicals a hardware store sells, be sure to read and follow all package directions.
There are a few different chemicals that are just as, or even more, effective at etching, but aren't as caustic and dangerous. They're more difficult to source, and are more expensive.
Much of the remedial cleaning can be avoided if the muriatic acid isn't allowed to dry after it's done its thing. As soon as it's played out wet it down just enough to keep the floor from drying, wait a few more minutes to make sure the acid's no longer active, and then use a lot of water to rinse it off.
Muriatic acid is one of the most caustic chemicals a hardware store sells, be sure to read and follow all package directions.
There are a few different chemicals that are just as, or even more, effective at etching, but aren't as caustic and dangerous. They're more difficult to source, and are more expensive.
Alpha thank you for that info, i figured a half hour-45 minutes of pressurewashing it after doing the muratic acid would be suffecient to rinse it off, guess not.....
so if i spend a couple hours tomorow night pressure washing it and scrubbing it down again with a bristle brush and then another rinse do you think it will be safe, is there any way i can tell?
so if i spend a couple hours tomorow night pressure washing it and scrubbing it down again with a bristle brush and then another rinse do you think it will be safe, is there any way i can tell?
AlphaGarage
Well-known member
I woulda thought that woulda done it also! I'm no chemist, but this isn't just a sand on the sidewalk type situation. There is quite a bit of chemical reaction going on when the acid hits the floor, I mean it's enough to be dissolving concrete, that's pretty tough stuff! When the water is allowed to dry the residue in no longer in suspension, so I'm guessing it quickly reforms a bond with something in the concrete. Clearly a bond that's not easily broken. If there's a next time do not let the stuff dry out. (don't you love 20/20?)
Call your acrylic coating supplier and get their recommendation about your next step.
Jaguar Fan
Well-known member
Malodin, In addition to all the advice, make sure you let the surface dry very well. Call the company that supplies the sealer and ask someone in tech support or an applications engineer just how dry the slab needs to be & follow their advice.
Do you have a vapor barrier underneath the slab? Where are you located - is it a dry climate or a humid one? Don't be surprised if you need to let it dry for two weeks.
Do you have a vapor barrier underneath the slab? Where are you located - is it a dry climate or a humid one? Don't be surprised if you need to let it dry for two weeks.
JakeD
Well-known member
Calcium chloride is the result of that reaction, a salt, and likely to be what that white powder is, in my opinion.
AlphaGarage
Well-known member
I think you might be right, I may have got the chemistry wrong. At any rate you want to try avoid it.
rinny_tin_tin
Well-known member
Are you sure that is a powder film and not just discoloration as the cement tries to dry? It could take a while before the concrete reaches a uniform color - especially if the slab it protected from the Sun by the roof. However, it does look like they burned the **** out of the slab by overfloating (based on pics)
thegarageguy
Well-known member
I have read this thread over and over and I can't seem to find any mention of neutralizing the acid with ammonia or baking soda.
Kevin54
MEMBER EMERITUS
That would be my thought. I always thought one was supposed to neutralize the acid after using it or what was soaked into the concrete would continue to work on it.
benjamming
Well-known member
The solution to pollution is dilution! Ha.
AlphaGarage
Well-known member
Good reason to read the product instructions and not rely on online info exclusively. Our instructions have quite a bit more info than can be effectively posted here.
Fortunately they're easy to email. If anyone wants a copy drop me a PM, email or phone call.
Fortunately they're easy to email. If anyone wants a copy drop me a PM, email or phone call.
The calcium in the concrete neutralizes all of the acid. What is left are salts. Pour acid on concrete and push it around until it stops fizzing and you can walk in it barefoot as it has turned into dirty salt water. I used to clean pools barefoot all day long.
funny but spot on. lots of water to dilute and carry off the salts. A hot water flood would work even better. Is the water heater nearby? hook up a hose to the drain valve and kill two birds at once flush the heater and the floor.
Any salts remaining will reduce adhesion.
Another issue might be efflorescence.
AlphaGarage
Well-known member
It's still a good idea to neutralize the acid wash. If there's not enough calcium to interact some of the acid may still be "hot." It's also possible that some of the slightly active acid migrates into the concrete. At a later date, after the coating has been applied, hydrostatic pressure could force up the acid. It won't have a lot of interaction with the backside of the coating, but it could interact with the concrete, dissolving it from underneath the coating, leaving the coating adhered to - nothing.
That scenario doesn't happen too often, but it has happened. It doesn't take much to neutralize the acid, and it can help avoid a coating failure. Plus you're not going to be rinsing acid over your landscaping and into the storm drain system.
That scenario doesn't happen too often, but it has happened. It doesn't take much to neutralize the acid, and it can help avoid a coating failure. Plus you're not going to be rinsing acid over your landscaping and into the storm drain system.
thegarageguy
Well-known member
May be safe enough to just walk on barefoot but when it comes to coating and or sealers you definitely need to neutralize. Hazing, blushing, bubbling and even delamination is common when it's not.
Ammonia or backing soda and a little effort and time will go a long way to assure you a good surface to seal or coat.