# Question about grout ~ help!!



## sean33 (Oct 11, 2006)

Hi all,

Try my first attempt on landscape construction with polystyrene foam and grout. I now facing some problem on grouting. I put a thin first layer of grout on the foam landscape and let it cured for 3 days. To be on the safe side I tested the hardness of this "crust" before laying anymore layers of grout and found that this crust is chipping off and crumbly. Is this normal for the base layer of grout? Will the strength improves with more layers? Any advice and information will be greatly appreciated !! Thanks!


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## VivariumWorks (Feb 27, 2008)

Hey, its a long and complex topic that isn't talked enough in detail so I've summed up some the key issues with using grout and offered some reasons why you are seeing what you are, how to fix it, and how to cure it. Hope this help and good luck on the build!

Grout is a mixture of various metal oxides for colorants, sand of various sizes, and portland cement (the glue). Due to it's specific intended purpose it isn't designed to be super strong as most of it's strength comes from the tiles on either side of it, and why most non-sanded grouts are recommended only for small thin sections and the 'sanded grout' for the larger sections/spaces as the large sand they use acts as a sort of aggregate and stabilizer. It is designed and used in a much higher water/cement binder ratio than standard cement (which uses the same 'glue') and sometimes will contain various additives to assist with binding to other cement/rock materials, but typically results in a very high water/cement ratio. The higher the w/c ratio, the more water takes up space in the rock matrix when drying/curing. The excess pore water evaporates out and the result is a low strength material due to: low total binder concentration, high water concentration, and in our case a thin layer.

So how this is relevant to us is that, yes what you are seeing is to be expected. Grout when used for our purposes, as a layup material over foam to make backgrounds/fake rocks, is to be used in multiple layers. First a base layer, usually a dark color, then followed up with one or two detail and color layers. With each layer you loose detail of the rock look you carved out of the foam, so less is better so as to not lose all of your hard carving work, but you still need a thick enough layer to be strong. Its basically finding what will be strong enough to work for your application and leave it at that.

So yes you'll want to put one or two more layers on top if it's just for dart frogs. You can also try lowering the amount of water you mix with the grout so it will brush on thicker.

Curing will be important. It just drying won't be enough. It will need to stay moist (not submerged) for a minimum of 28 days. This so the dicalcium silicate in the portland cement can fully hydrate. This reaction is very slow and takes a full 28 days to happen, and even then it never really stops, just slows down to a very small amount. The issue for us is that as the cement hydrates it puts out CaOH (calcium hydroxide or lye). This is crazy basic and will shoot your water and soil's pH sky high and kill your plants and base burn your frogs. So the issue here is that when you cure your grout, it needs to cure wet, but not submerged, for a full 28 days to let the reaction fully happen and leach out as much as possible into water you'll toss. Just because your pH is good on day 8 or 10 because you poured acid over it, as it's falsely believed will help, the pH will rise again from day 10-28 as the rest of the dicalcium silicate and other cement products continue to hydrate and kick out CaOH.

So make your background, put it into your tank, and before you put anything into it pour water over it, leaving a pool of water in the bottom of the tank, and cover the top with plastic wrap and leave it for a month. You want water to soak up into your grout layer from the bottom by wicking. It would be good to occasionally change out the water in the tank as you want a strong gradient pulling the CaOH from the grout's pore water and into the waste water.

Some people, myself in the past, have thought to simply trap the CaOH inside the grout by sealing it. All sorts of stuff has been suggested and used. Epoxy, polyester/'fiberglass' resin, silicone caulk, waxes of all sorts. None of this works long term. The reason for this is that the CaOH and water will find a way. It wants to due to diffusion, and unless you have a perfect seal, it will find a way, and leach the strong base into the water/soil and slowly poison the tank/water. Obviously there's a million other factors in play, and not everybody will see the same effects as the organic acids in the soil can help to counteract the leaching out base, but the simple fact is that it can, will, and has killed many many many an animal/tank. So toss out the old idea that you can seal it quick and skip the month long curing process. It sucks that we have to do this, but that's the trade off. You want a cheap, rock-looking, easy to buy, waterproof, laminating material? You go with grout. BUT, you have to do it right or your plants and critters (and subsequent pocketbook) will pay for it down the road.


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## sean33 (Oct 11, 2006)

Thank you thank you thank you VivariumWorks!! This is perhaps the most informative writing on this issue~ 

Another thing which puzzles me,how long should we wait for each layer of grout to cure before the next is laid?


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## VivariumWorks (Feb 27, 2008)

As soon as it's dry enough to take on the next layer. The grouting process shouldn't take you more than a single afternoon. Base layer on thick and dark, dry in sun, recoat with color, dry in sun, final detail/colors layer, dry in sun. Then go about curing it. But you'll want it to be dried out and set before going for the curing step.


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## Bunsincunsin (Feb 11, 2008)

Is there a particular type of foam that works best with grout - or a particular type that you would recommend?


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## oldlady25715 (Nov 17, 2007)

In short keep it wet till the PH goes down. I've covered in plastic and misted 2-3x a day to keep moist, but it takes a while to cure this way (like a month)

I think it looks far better than coco fiber and bark as a background.


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## diggenem (Sep 2, 2011)

I have a question and do not intend to hijack, but how long will it take to cure if you just let the background sit? I have a tank that I made a grout rockwall in and it has sat empty for about a year and a half.


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## sean33 (Oct 11, 2006)

Most of the grout available contain anti mold agent. Is it safe to use?


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## VivariumWorks (Feb 27, 2008)

It only cures when sufficient water is available for it to. The chemical hydration reaction stops when no water is present. If it's very humid, it will help, but if it's kept dry, it probably hasn't cured much since it first dried out. 

I don't know much about the anti-mold agents honestly. To say it is or is not safe I'd need to know what type is used, it's likely mobility in the vivarium, and it's relative concentration. But that's an area I haven't researched a whole lot.


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## VivariumWorks (Feb 27, 2008)

As for the foam, it's been suggested to try to avoid normal stryo-foam, and go with an EPS foam or other type. Straight stryofoam has been suggested as a possible endocrine disruptor if the sytrene is able to leach out into the water, which when heated/melted/carved can allow to happen. So sticking with at minimum an Extruded Polystyrene foam (the pink/blue insulation board foam at Home Depot/Lowes) or a polyurethane foam, is suggested to be better than typical styrofoam. The other thing is that you can get much better detail carved into this material as it doesn't have the large beads pressure heated together.


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## sean33 (Oct 11, 2006)

Thanks VivariumWorks.
Now the sculpting and grouting stage are over and I put the whole structure inside the tank as you've suggested and start the month long curing stage. I pour water over the whole thing and leave a thin layer of water at the bottom. On top of that I hooked up a fogger connected to a timer to make sure that it is humid enough for the curing process. Any comment? Thanks~


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## Dendro Dave (Aug 2, 2005)

VivariumWorks said:


> As for the foam, it's been suggested to try to avoid normal stryo-foam, and go with an EPS foam or other type. Straight stryofoam has been suggested as a possible endocrine disruptor if the sytrene is able to leach out into the water, which when heated/melted/carved can allow to happen. So sticking with at minimum an Extruded Polystyrene foam (the pink/blue insulation board foam at Home Depot/Lowes) or a polyurethane foam, is suggested to be better than typical styrofoam. The other thing is that you can get much better detail carved into this material as it doesn't have the large beads pressure heated together.


I've been thinking of using regular styrofoam since I have so much of it around. My problem is it melts when you try to paint it with most stuff...So I was going to seal it in grout/thin cement, and then actually paint over that...and possibly seal it with clear plasti dip or clear urethane. Do you see any leaching issues there, or any reason why that wouldn't work?


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