# Vinegar changed the color of my cement



## marketingman (Apr 24, 2014)

I have been working on cement water features for my viv for what seems like months. I let the cement cure for about 3-4 weeks and then 3 days ago started with (white) vinegar baths to reduce the PH. Today was going to be my last day so I could [finally] start painting. I gave it a good rinse with water and let it sit in front of a fan for a couple hours. Here is what it looks like now - is this normal?

(first picture is what it looks like now, second is what it looked like before)


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## JimO (May 14, 2010)

Did you happen to use some white sand as an aggregate for the cement?


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## marketingman (Apr 24, 2014)

JimO said:


> Did you happen to use some white sand as an aggregate for the cement?


No, I didn't use any sand. I used Quikrete quick set mortar. The first few coats were used with acrylic fortifier instead of water and the last couple coats were with water. The areas where water was the liquid are twice as white as the areas where acrylic fortifier was the liquid.

This is my first time ever using cement - could this be calcium or maybe just residue from the white vinegar?


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## Ray (May 12, 2009)

My guess would be oxidation of the small amount of iron in the cement by the acid, giving it a green cast.


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## Okapi (Oct 12, 2007)

Is this the first time that you have let it get completely dry? I bet if you let it get soaking wet again it will be dark again (until it dries out again).


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## Pumilo (Sep 4, 2010)

When I used to manufacture artificial "live" rock for coral reefs, we used Portland cement. After the curing process, the rocks would be coated in a scaly, flaky, white residue, that was most obvious after drying. It was always worse if we didn't keep up on water changes throughout the cure. We found it scrubbed away very easily with a wet scrub brush. I don't know if you are seeing the same problem or not. 
I should point out that my artificial reef rocks, did have a large portion of calcium (aragonite sand and/or oyster shell) in the mix.


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## marketingman (Apr 24, 2014)

Okapi said:


> Is this the first time that you have let it get completely dry? I bet if you let it get soaking wet again it will be dark again (until it dries out again).


It's the first time I've put it in front of a fan to dry, but during the curing it would get dry occasionally. I didn't put it in a 24/hr soak and would spray it with a spray bottle as often as I could. By the time I would get home from work it would be pretty dry, but never white. I followed the same process for the vinegar (spray bottle) and this was the first time I let it dry completely after the vinegar portion.



Pumilo said:


> When I used to manufacture artificial "live" rock for coral reefs, we used Portland cement. After the curing process, the rocks would be coated in a scaly, flaky, white residue, that was most obvious after drying. It was always worse if we didn't keep up on water changes throughout the cure. We found it scrubbed away very easily with a wet scrub brush. I don't know if you are seeing the same problem or not.
> I should point out that my artificial reef rocks, did have a large portion of calcium (aragonite sand and/or oyster shell) in the mix.


Is this white residue due to the presence of calcium found in the mortar? Will it hurt any animals if I don't scrub it? My next two steps are paint and seal (Krylon polyurethane seal). Will that lock in any harmful chemicals that may have come from the curing and vinegar?


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## JimO (May 14, 2010)

My guess is that the white residue is calcium acetate, which is white, that formed from the reaction of the vinegar (acetic acid) with the various calcium silicate compounds that make up cement.


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## marketingman (Apr 24, 2014)

JimO said:


> My guess is that the white residue is calcium acetate, which is white, that formed from the reaction of the vinegar (acetic acid) with the various calcium silicate compounds that make up cement.


Is that a good thing lol? Does that mean the vinegar did it's job so the animals and plants don't have to deal with the high PH?


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## VivariumWorks (Feb 27, 2008)

It's either the precipitate from the vinegar and the calcium hydroxide or it may be the vinegar reacted with the acrylic fortifier. It's possible it's both but my guess is the fortifier. If you look into the chemistry of most of them they are based on a PVA. Which will react with the acetic acid. 

(Also, a thing to note for future builds, is that most cement additives/fortifiers are NOT waterPROOF. They are water-resistant but not proof. Most will even state this on the bottle in the form of "not designed for use with pools or standing water applications". The good thing is that even if the PVA does leach into the system it's unlike to cause a lot of issues. But an example of this can be seen when guys would make the acrylic fortifier/peat mix 'flevopol' that was all the rage back in the day, and it would then break apart when the water hydrolyzed the PVA over time, most notably in the waterfall/dripper tanks.)

I'd suggest testing the water feature. Dunk it in tap water and see what your pH is after a day. If it's above a 9, I'd let it cure some more. If it's a 9 or less it should be ok enough for any excess to be eaten up the vivarium's humic acids.

Even though you cured it for a long time, just keep in mind it takes time to remove the CaOH from the grout because of the water needing to move into the grout's pores solubilize the CaOH, and then migrate back out of the pores via diffusion. It can take a while. Frequent water changes and water movement (pump) will speed it up.

Adding the sealant and paint will reduce the diffusion migration from the grout into the vivarium, but make no mistake it will happen. It will take time and the sealing will slow down the rate, but remaining CaOH will either react with Co2/water to make calcium carbonate, or migrate in the vivarium water and raise the pH until it reacts with some kind of organic acid.

As with anything, the dose makes the poison. If you have already done a good job of curing it and reduced the amount of excess CaOH left over from the curing, the amount that can leach can be small enough to be mitigated by the vivarium. It's when there is an over abundance that the vivarium soil and water can't buffer/react is when you get a raise in the pH and can be problematic. 

I've been working on a way to mitigate all of these various issues for years now and I'm getting closer and closer. Eventually I hope to have a grout-like material that should set, cure, and be viv ready in less than a week or faster. But, as with everything, it just takes lots of time, money, and tests. Lots and lots and lots of test. 

Hang in there with it and don't give up on it. I'm 6 years in on my grout replacement material and as long as it's fun it's all worth it. As far as grout builds go yours is really good and you're asking the right questions.


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## marketingman (Apr 24, 2014)

VivariumWorks said:


> It's either the precipitate from the vinegar and the calcium hydroxide or it may be the vinegar reacted with the acrylic fortifier. It's possible it's both but my guess is the fortifier. If you look into the chemistry of most of them they are based on a PVA. Which will react with the acetic acid.
> 
> (Also, a thing to note for future builds, is that most cement additives/fortifiers are NOT waterPROOF. They are water-resistant but not proof. Most will even state this on the bottle in the form of "not designed for use with pools or standing water applications". The good thing is that even if the PVA does leach into the system it's unlike to cause a lot of issues. But an example of this can be seen when guys would make the acrylic fortifier/peat mix 'flevopol' that was all the rage back in the day, and it would then break apart when the water hydrolyzed the PVA over time, most notably in the waterfall/dripper tanks.)
> 
> ...


Well, you just sold me on buying whatever you sell without even trying to sell me anything lol. Will definitely be checking out your site! Thank you so much for taking the time to write such a lengthy and informative response!!


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## VivariumWorks (Feb 27, 2008)

No problem, hope I can help. This issue is something that's been something that's been interesting to me for a while now.

As for the quickest way to cure portland cement products, (concrete, grout) one way to speed it up, during the month long cure process is to make a waterfalling CO2 box.

The way it works when they make a slab of cement is they keep it wet so the water can react with the powder and allow the reaction to take place. As that happens it kicks out the high pH forming CaOH (calcium hydroxide or lye). This normal and supposed to happen. For us that's bad though. So the way it reacts in the outdoors is water in the pores mixes with atmospheric CO2 to make carbonic acid. (Reason the oceans are acidifying due to CO2/climate change.) This carbonic acid can then react with the cement's reaction product, CaOH, to form CaCO3 (calcium carbonate). This is what most limestone and coral is made from and in most calcium supplements we and our frogs eat.

Thing is you can't just buy carbonic acid because it only exists when the CO2 gas is dissolved in water, and the amount and ease it can do so is temperature dependent. The lower the temp the more CO2 gas water can hold. 

So for our purposes, what one can do is take a big plastic storage tote from HomeDepot/Lowes. Make a hole in the top to fit a cord through. Then fill the bottom with about 3-4" of water. Then put a pump into the water and attach a hose to it. Run the hose to the top of the container and make it spray via a spraybar (pvc with holes) or a spray head. So it's sprinkling all over the inside of the bucket. Then get some dry ice. (Solid/frozen Co2.) Do this outside, preferably. Then drop in the dry ice into the tote. The pump cord hole will let air out, but CO2 stay in because it's heavier than air. The spraybar makes high surface area to volume drops which increases water/Co2 reaction and increase carbonic acid formation. This then drips onto your design, and begins to react with any of the CaOH you need to remove. This basically speeds up the natural process by increasing the amount of the limiting reagent in the reaction we want. It's by no means a one day cure as cement usually takes 28 days to fully hydrate but this will help you have it ready faster after that time period.

Just don't overdo the C02 in the tote and build up pressure. That's bad. Unless you DO have a very strong steel pressure vessel rated to hold high pressures like a pressure cooker. This is how they force cure cement in some parts of the construction industry. By forcing pressurized CO2 it helps increase the water/Co2 ratio, helping for force the reaction even more. And if you have a super-critical-fluid-extractor handy, well, you can cure cement in a day by letting the C02 get to supercritical and then let it move through your solid objects curing everything along the way instantly because supercrit fluid is just cool like that.

But yea, for us normal people, plastic totes, a pump, and a little dry ice works and is going to be about as close as we can get on the small DIY scale to this.

And in theory the vinegar or citric acid baths are supposed to do this, but these can attack your PVA binder and the actual cement it'self unlike the carbonic acid which is much weaker.

(Daily unneeded cement science lesson over. lol)


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