# Great Stuff/Silicone Question



## Rick H. (Feb 22, 2007)

Hi all,

I am considering building my first terrarium with a background and have been doing much research on construction techniques. It seems that the majority of people use a combination of polyurethane foam and silicone to shape the background and then cover it with some sort of organic material (coco bedding or sphagnum) for looks and to help plants root.

I have seen some posts where people spray on the great stuff and then add the organic material right away. Others spray the great stuff, smear silicone all over it, and then add the organic material.

My main question is why do some people cover the great stuff with silicone? Does this simply help the organic material stick or does it seal the great stuff? Does the great stuff need to be sealed to keep out water or prevent chemicals from leaching into the vivarium (i.e. is it toxic when cured; I have read that it is not but need some reassurance)?

I guess it comes down to the fact that I get WHAT other people are doing but I don't understand WHY it is being done that way. Your help/advice is greatly appreciated!

Rick


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## AaronAcker (Aug 15, 2007)

One reason for using silicone after the foam is that the foam color is yellow, and if coco bedding comes off or a spot is missed than you'd have yellow blotches. I myself us the black foam (pond/waterfall great stuff) and apply the coco bedding directly to the foam. If I miss a spot than i touch it up using silicone. The main reason I do it this way is simply personal preference. I just dont want to deal with that much silicone.


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## skronkykong (Jan 1, 2007)

I just made a viv using black expanding foam (for waterfalls) and applied peat moss directly to it. I tried many different approaches to doing this but in the end most of the peat moss fell off. It still looked pretty good but nowhere near as good as using silicone. 

Also the silicone helps water proof the GS. I would use brown silicone instead of black as well. I used brown this time and I like it a lot better. There are always going to be places that all the organic matter falls off leaving exposed silicone or expanding foam. Its better to see brown or black silicone than GS. Yellow GS just looks so ugly peaking through a nice brown background.


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## defaced (May 23, 2005)

GS is water proof. It's a closed cell polyurethane foam. 



> I just made a viv using black expanding foam (for waterfalls) and applied peat moss directly to it. I tried many different approaches to doing this but in the end most of the peat moss fell off. It still looked pretty good but nowhere near as good as using silicone.


This is the consensus of how the experience goes. I'd not recommend it to anyone. 

Rick, you may want to look into the concrete binder method. It's a bit more involved/expensive than the silicone/filler method, but I prefer the results and can say from experience it holds up very well.


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## jdogfunk99 (Oct 16, 2007)

Two things: 1) GS remains sticky for a *very *short period of time and when you try to push coco or peat into it, it will collapse under pressure into a goopy mess. 2) GS *is *waterproof, I use it for my pond and it's submerged 24/7.


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## Rick H. (Feb 22, 2007)

Thanks for the help everyone.

It sounds like the silicone is used mainly for aesthetic reasons. Anyone out there want to reassure me that cured great stuff in nontoxic?

Can anyone briefly describe the concrete binder method so I can get a pool of terms to search with?

Thanks for the collective wisdom/advice.

Rick


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## defaced (May 23, 2005)

Put "ace concrete" into the search and change the "Forum" drop down to the P&C section.

There is no conclusive proof if GS is, or is not, toxic. Empirically, it doesn't seem to be a problem, but analytically, there are some things that we're not sure of. If you want to dig into the GS toxicity issue, search this section for a thread titled "A conversation with Dow", or something like that. Blort is the thread starter if I remember right.


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## dragonfrog (Feb 16, 2006)

Personally, I have steered away from the GS school of thought for a few reasons. 1). It is way too messy to deal with. 2). Takes too long to fully cure to the point that you can use the viv. and 3). It is rather soft and does not hold well when hanging things from it.

I now use exclusively, cork bark. You can get it in pretty flat pieces near the size of your tank wall. And it is extremely easy to cut and silicone to the side of the tank. It looks very natural. And best of all, when you want to mount a large heavy brom, it holds to the bark much better.


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## jdogfunk99 (Oct 16, 2007)

dragonfrog said:


> Personally, I have steered away from the GS school of thought for a few reasons. 1). It is way too messy to deal with. 2). Takes too long to fully cure to the point that you can use the viv. and 3). It is rather soft and does not hold well when hanging things from it.
> 
> I now use exclusively, cork bark. You can get it in pretty flat pieces near the size of your tank wall. And it is extremely easy to cut and silicone to the side of the tank. It looks very natural. And best of all, when you want to mount a large heavy brom, it holds to the bark much better.


Steve, were do you buy your cork bark, and what do you put between the pieces (I assume they don't fit together like a jigsaw puzzle)?


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## Sokretys (Dec 16, 2007)

some people have mentioned their peat moss falling off of the silicone? this happened to me on a corner of my viv. it was the place i had packed down. im guessing that it works best when packed down quite firmly..and letting the silicone set for a bit. i let it sit for 30 minutes after the first round of it before i vacuumed it off. i also used the brown silicone it worked great. just get some latex gloves for tthe GSing and siliconing. i promise you wont regret it. what was that about concrete whawha? 

-Nate


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