# Great Stuff Warning



## Nath514 (Jul 8, 2012)

Never Ever Ever, spray down a really thick layer of greatstuff. If you need a thick chunk do it in stages. I went a little to thick and ended up with a natural disaster in my tank. The outer inch cured but that was it the inside collapsed into a disgustingly thick sticky slurry of fail. Took me three hours to cut the outer foam away and try to remove all the gooey uncured foam.

Lesson Learned


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## Pumilo (Sep 4, 2010)

It can also swell so much that it cracks the glass if you put it on too thick.


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## Nath514 (Jul 8, 2012)

Pumilo said:


> It can also swell so much that it cracks the glass if you put it on too thick.


Certainly can, I use it very sparingly in confined spaces.


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## gardennub (Dec 10, 2011)

Don't forget to sand in between layers! Also if you accidentally put it on too thick something that may help it cure is to poke holes in it. This must be done fairly early in the curing process though


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## BlueRidge (Jun 12, 2010)

Pumilo said:


> It can also swell so much that it cracks the glass if you put it on too thick.


Yep, seen that happen. I've also seen great stuff crack PVC pipes when used as a gap filler. Definitely go easy with that trigger.


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## Nath514 (Jul 8, 2012)

I think cracked glass might actually be easier to fix than when it doesn't cure. It is so sticky, really hard to get off of everything.


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## Dane (Aug 19, 2004)

If you need to fill a big space, rather than using all spray foam, you can use some chunks of polystyrene or other material as filler, and just GS over them.


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## Nath514 (Jul 8, 2012)

In this instance I used way more than I needed just so that I would have lots of room to carve down the foam to form the shapes and structures I wanted.


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## Pacblu202 (May 8, 2012)

Dane said:


> If you need to fill a big space, rather than using all spray foam, you can use some chunks of polystyrene or other material as filler, and just GS over them.


Problem with polystyrene is its potentially linked to being an inhibitor in the tabks inhabitants. If its completely covered it might not have an affect but that's up to you to decide


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## Rusty_Shackleford (Sep 2, 2010)

Pacblu202 said:


> Problem with polystyrene is its potentially linked to being an inhibitor in the tabks inhabitants. If its completely covered it might not have an affect but that's up to you to decide


I think the actual term you're looking for is "endocrine disruptor"


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## carola1155 (Sep 10, 2007)

Jon beat me to it while I was digging up this post... but yes... Endocrine Disruptor

In the entertaining words of Doug:
http://www.dendroboard.com/forum/me...6-simple-functional-jbear-way.html#post707364


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## Pacblu202 (May 8, 2012)

There ya go Jon! I always seem to forget the actual name


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## Gamble (Aug 1, 2010)

This is why i havent attempted to use GS. 
Yea it makes for some great backgrounds, but all the work involved in getting to that point just seems like too much of a pain IMO.


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## Nath514 (Jul 8, 2012)

Its really not much work at all when things go right. You spray wait a few hours and carve with a steak knife.


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## Steve88W (Jan 21, 2011)

Let each layer cure! (I give it 24 hours per application)
If it's too thick, the underside won't cure correctly and may end up with a hallowed out backing which can lead to collapse.

If you notice a hollowed out area, I usually jam the straw through the dried foam into the opening and inject a small amount of new foam to seal it all up. Don't over do it as it will expand.

I can normally build a nice background with only one application of foam per side. 

Oh... and use gloves.
This stuff is Gorilla Glue and would LOVE to bond to your skin and clothing along with any dirt making you look like a leper.


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## Nath514 (Jul 8, 2012)

Steve88W said:


> Let each layer cure! (I give it 24 hours per application)
> If it's too thick, the underside won't cure correctly and may end up with a hallowed out backing which can lead to collapse.
> 
> If you notice a hollowed out area, I usually jam the straw through the dried foam into the opening and inject a small amount of new foam to seal it all up. Don't over do it as it will expand.
> ...


I thought about doing this but I am worried that the gooey inside will never cure and leach dangerous chemicals. So I am hesitant to just fill in the hole with more foam.


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## Dane (Aug 19, 2004)

Pacblu202 said:


> Problem with polystyrene is its potentially linked to being an inhibitor in the tabks inhabitants. If its completely covered it might not have an affect but that's up to you to decide


I wouldn't have suggested it if it was to remain bare, but if it's sealed off from the water table and contact with the inhabitants, it's no big deal.


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## Pacblu202 (May 8, 2012)

Gamble said:


> This is why i havent attempted to use GS.
> Yea it makes for some great backgrounds, but all the work involved in getting to that point just seems like too much of a pain IMO.


It really isn't that much. I think people just get excited doing it. I've made numerous tanks with GS and since the beginning they have all turned out fine. They are the easiest thing to do as long as you control it. I have gotten to the point where I barely have to carve anything because its just easy to manipulate it while your doing/ 30 mins after laying a coat when the outer skin forms


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## Rusty_Shackleford (Sep 2, 2010)

I agree. Doing a GS background like I just did on my 55 gal build is half the fun of building a new viv.


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## coryh83 (Jul 28, 2012)

The great stuff I just used ended up with a few air pockets. I just waited a few days till it fully cured and then ripped off the top layer. I was then able to add another thinner layer. I have worked with GS a lot over the years and have found that it could take days to fully cure.


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## Nath514 (Jul 8, 2012)

Very ironic that I posted this warning yesterday. I then went home to put down some new GS finished up then tripped and put my hand, which I had just removed my glove from, directly into my test pile. The house still smells like paint thinner from me frantically trying to get it off.


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## frankpayne32 (Mar 17, 2007)

I am currently having the exact opposite problem in my build. I am experiencing a contraction and overall shrinkage (hehe) of the GS after I have applied a layer of Drylok to it. Anyone ever see this? In the pic you can see how the background has shrunk away from the glass.


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## BlueRidge (Jun 12, 2010)

That happens when you use Titebond also, it tends to pull the GS away from the glass.


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## Nath514 (Jul 8, 2012)

Which GS product are you using. Some do contract more than others you should always make sure the foam is completely cured and done expanding / contracting before moving to the next step. ( although I admit that is awfully hard to do )


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