# Grout curing time?



## KCarter90 (Jan 25, 2019)

Hey folks, 

Need some advice on grouting. 

I’m currently working on a project & I am now at the stage of grouting my polystyrene/expanding foam ‘rock’ background. 

I have done what seems like hours of research on this build but I’m still unsure about one area... the curing time for grout.

I’ve heard three different times for curing... 1 week, 2 weeks & 1 month, during which the grouted areas need to be kept moist or in high humidity during the curing process. 

It’s worth mentioning that once completed the vivarium will be bioactive and will remain at around 60 - 80% humidity with peaks of 100% humidity in the morning & evening. 

So my questions are:

How long does the grout take to cure so it is safe for my reptile & plants?
&
Is there a faster method for curing the grout? (I will be painting the grout with acrylic paint & sealing with mod podge) 

I’m a reef hobbyist so I do understand that patience & allowing things to occur naturally is sometimes just the way it has to be, but if there is a safe way to cure the grout faster I’m all ears. 

Thanks in advance!


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## charoozz520 (Dec 8, 2008)

Hello fellow reefer!

I have done a few grout backgrounds before and I would say it usually took a week or so before I set them up for my inhabitants. Just remember that you need to apply several layers of grout and that's why it takes so long, if you don't apply a thick enough layer the grout will start to crack and peel which is not fun. I usually let the layer dry then spray it with water then let it dry again. Also did you get sanded or non sanded grout? I usually like to sprinkle some sand in between the layers of grout to give it more texture.

Same goes for modge podge you want to get a good seal and that usually takes a few layers. 

Here are some pictures of the one's I have done with grout:

















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## davecalk (Dec 17, 2008)

The problem is that people mean different things when they talk about "curing".

Most concrete is used in the building industry and in roads / driveways / sidewalks, etc. where strength is the crucial factor. Therefore in the concrete industry when they talk about cure time they are referring to the time it takes to get to a certain level of strength. 

After being poured, concrete typically is at 16 % of it's full strength after one day, 40 % in 3 days, 65% in 7 days, 90% in 14 days and 99% strength in 28 days.











"Cure" time is dependent on many factors: moisture levels, temperature levels, time, and the chemistry of the concrete mix. There is also a difference between "curing" and "drying". If a concrete drys before it is properly cured, it often is very comprised. This is because when concrete dries out, it kind of dies and quits curing, just as a tomato seedling would die if it weren’t watered.


*How Concrete Curing Affects Our Frogs*
Most of the curing issues discussed in the concrete industry are irrelevant to us and our frogs. The main issues that concern us, our frogs and the tanks they live in tend to center around the high pH levels of concrete / grout.

Fresh cement can actually be dangerous to the skin is because of its high pH. Cement is incredibly alkaline, with a pH of 12 to 13. 
(The pH scale runs from zero (very acidic) to 14 (very alkaline.)

Water, which has a pH of 7, is considered pH neutral. Human skin is slightly acidic at pH 4.5. This means the pH of cement is vastly different from that of human skin. Because the pH scale is logarithmic (and each whole number change indicates the pH changes 10-fold), wet cement has a pH one billion times higher than human skin. 

When skin is exposed to higher pH levels, it becomes more permeable; it more easily absorbs chemicals. For this reason, any chemicals leaching out of the cement can quickly irritate the skin and even enter the bloodstream. It is vastly worse for our frog's with their moist and permeable skin.


The high moisture levels in our tanks will actually bring additional hydroxides (alkalis) to the surface of the grout / concrete which will actually cause the pH levels at the surface to increase because water through osmosis actually pulls Alkaline salts to the surface where our frog's permeable skin can absorb them.



This is an image of the process of effervescence.









*How can we "cure" & lower the pH in the concrete / grout *

Here are some Dendroboard discussions about "Curing" the pH issue that affects our tanks.

Discussions of Curing grout. 

Using Vinegar to help cure Grout & some of the issues. 

Grout Questions.


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## jgragg (Nov 23, 2009)

> when concrete dries out, it kind of dies and quits curing, just as a tomato seedling would die if it weren’t watered


This is an important point that is easy to overlook. Dried does not equal cured. Cured does not equal dried. Portland cement will cure perfectly well underwater - think about poured bridge footings on the bed of a river or bay.

When doing grout-based backgrounds, typically with multiple thin layers, it's really easy to screw up and let the grout desiccate. (With each additional layer, you get a little more wiggle room - and the first layer is especially vulnerable.) 

I stopped using the grout method about a decade ago (switching to epoxy for fake rock, and cork mosaic when no "rock" is desired). But when I was using that method, I was always careful to seal the job pretty air-tight as it was curing, and also to mist it frequently. 

The cure curves (99% strength at a month) are right on. If you want a strong background - one that's maximally resistant to dings when you're in there messing around trimming plants or whatever - keep your background moist for a couple weeks at least. Four weeks will give you a bomber background.



> let the layer dry then spray it with water then let it dry again


This "works" (you will get a background done) but it leads to a weaker project. In particular I think it invites delamination of the built-up layers. I don't think it's good practice, for a truly durable job. It probably holds up to light duty, but...it's hardly any more effort to do it right the first time. And it's way less effort down the road.

Good luck OP.


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## KCarter90 (Jan 25, 2019)

Thank you for the replies & i appreciate the detailed explanations.

I've had the background curing for just over 2 weeks; spraying it as often as i can to keep it moist. 

When i talk about curing i had in mind the length of time it would take for the grout to be considered 'safe' so as to not harm the plants/animals. So are we saying that after 2 weeks it is no longer considered harmful, but 4 weeks is to allow the grout to be at its maximum strength?

Thanks.


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## jgragg (Nov 23, 2009)

Oh man, that's a whole 'nother topic, which I am not really qualified to speak on. I'll venture however, that cured does not equal "safe". It's still alkaline as hell. This is why - on the busier fish forums - there's so much discussion of soaking and water changes, or (ugh) using stronger acids (than plain water, I mean - like diluted vinegar) to drive down the pH when using Portland cement, either in little background builds, or in constructing full-on fish ponds.

And all this pH-management & -monitoring stuff - besides the basic "crafting hassle-factor" - is why I just said forget grout, and after some searching, went all-in with epoxy as my foam covering solution.

Anyway that's not helpful to you, nor what you want to hear. So I'll offer the "no regrets, and maybe even good enough" suggestion that you do some soaking and rinsing. You could get some pool & spa pH test strips and test the soak water after some time into each soak. You ought to be able to watch the pH go down, down, down. Where you're comfortable stopping at - that's for the frog guys here to answer. I'm actually a snake guy on DB to learn (the thought of my snakes laying on grout, getting chemical burns on their little bellies, was just intolerable to me). And of course I'm happy to share what I've learned by experience or research.

good luck!


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## davecalk (Dec 17, 2008)

jgragg said:


> Oh man, that's a whole 'nother topic, which I am not really qualified to speak on. I'll venture however, that cured does not equal "safe". It's still alkaline as hell. This is why - on the busier fish forums - there's so much discussion of soaking and water changes, or (ugh) using stronger acids (than plain water, I mean - like diluted vinegar) to drive down the pH when using Portland cement, either in little background builds, or in constructing full-on fish ponds.
> 
> And all this pH-management & -monitoring stuff - besides the basic "crafting hassle-factor" - is why I just said forget grout, and after some searching, went all-in with epoxy as my foam covering solution.
> 
> ...



Both of the above were right on regarding the question of when grout is "Safe". Curing does not kill the high pH of freshly cured grouts. Lowering and killing the high pH is the biggest problem with working with grout / concrete. I quit using it years ago as well for these very reasons. Again, not what you really want to hear. Our tanks with their high moisture levels will cause pH to continue to leach from the grout and our frogs with their porous skin are much more sensitive to the pH issue then are reptiles with their scales. 

Spraying the grout for a couple of weeks may cure it and strengthen it, but that will not deal with the high pH levels. 

Please read the links I posted above. 

You really should flush your rock creation with lots of water, with lots of water changes, for lots of days in order to kill the pH. Vinegar, or stronger acids, can help but it is not a cure all, it just helps quicken the process. If you use to strong of an acid you can damage your concrete.



jgragg uses epoxy to create backgrounds and rock. Me I use foam and have been very happy and have had in my tanks for years with no problems. 

Making Colored foam Rocks


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## davecalk (Dec 17, 2008)

jgragg said:


> This is an important point that is easy to overlook. Dried does not equal cured...
> 
> I stopped using the grout method about a decade ago (switching to epoxy for fake rock, and cork mosaic when no "rock" is desired). But when I was using that method, I was always careful to seal the job pretty air-tight as it was curing, and also to mist it frequently....
> 
> ...



Not trying to highjack the thread, but jgragg, I am curious. You made the statement that you felt that the methods that I suggested for creating One shot foam walls created weaker walls that are susceptible to delamination. Why do you say that? Have you had that happen? If done incorrectly by adding too much water between the layers I can see that happening, but that has not been my experience. Your thoughts?


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## KCarter90 (Jan 25, 2019)

Righto, I'll continue flushing the grout will water & i've ordered some PH strips! 
Is it maybe worth giving it a daily 'bath'?, ie. literally filling a bath or container with water and keeping it submerged for some time. Figured i could do this to flush it. 

My build is for a crested gecko, i just found this forum to be most reliable and active!

I'm pleased with how the grout looks, but i will use an alternative method to build a rock structure in the future.


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## jgragg (Nov 23, 2009)

> If you use to strong of an acid you can damage your concrete.


I'm glad you took the time to point this out. That's what my "ugh" was about.




> Not trying to highjack the thread, but jgragg, I am curious. You made the statement that you felt that _the methods that I suggested for creating One shot foam walls created weaker walls that are susceptible to delamination_. Why do you say that? Have you had that happen? If done incorrectly by adding too much water between the layers I can see that happening, but that has not been my experience. Your thoughts?


Oh no, I'm sorry, I must have been unclear. I was referring to grout (specifically, someone else's suggested technique), not foam. Actually I learned something useful from your foam advice, having had exactly that "deep goopy center" problem with expanding foam that I've sprayed too thick.



> jgragg uses epoxy to create backgrounds and rock. Me I use foam and have been very happy and have had in my tanks for years with no problems.


Actually I very often (not quite always, but usually) use foam too. Nowadays it's mostly extruded PS but also, still (much less than I used to), some expanding PU. But I have always worried about leaching, and also waterlogging & deterioration, so have always covered the foam with...something. In my explorations & tinkerings, which began around 1998 or so, I've tried pretty much everything to cover foam - grout, the "flevopol" method, silicone topped with organics and inorganics, stand-alone Drylok, and epoxy. 

Having tried pretty much everything, seeing (and I mean watching closely, with great curiosity and an eye to "next time"):

how different materials perform in the presence of humidity, flowing water, animals of different sizes & abilities, urates & feces, boisterous plants etc, 
how they appear aesthetically, 
what they're like to work with (relative ease to apply & texture, messiness, physical unpleasantness etc etc), 
and overall cost in dollars and hours
I'm a huge fan of epoxy, for its hard shell, ease of use, aquarium-safe waterproof sealing, relative harmlessness to my body, and ease of texturing & tinting/painting.

Anyway I hope the OP and any other readers take this not as a hijack, but just some well-intentioned sharing of experience and context. Some guys absolutely love grout, they master it and it is worth the trouble to them. (There was a Finn in particular I recall posting pics somewhere, who did some incredibly beautiful stuff.) Personally, after about 3 mediocre at best builds I just found it more trouble than it was worth - a little weird to apply, touchy to texture, brittle/a bit delicate when completed, not easy to seal to a waterproof nontoxic standard, alkaline as hell if not sealed, etc etc.

cheers


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