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Discussion Starter · #1 ·
So, having read multiple accounts of people's great stuff failing to adhere to aquarium glass, I took the advice advanced by NEHerp and first applied a layer of silicone to the interior glass. This was cured for several days before I took the next step and added the Great Stuff.

In both tanks, I had major adhesion problems, generally along the bottom, with the Great Stuff curing in a manner where it has a big gap between it and the glass. On one wall of a 10, it was so bad I had to just cut the whole flap away.







So my questions: why did this happen, what did I do wrong, and how can I now fix this?


I'm concerned that if I go back and spray in MORE great stuff, it's going to expand and "push away" the existing adhered sections, just creating an even bigger headache.
 

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I had the same problem as you first time was my fault I just used the GS straight to the glass and it pulled away in the center all the way to the bottum. second time I used silicone and let it sit for 4 or 5 days and then used the great stuff and it pulled away again this time just the bottom. so I just pulled it all out and used silicone to glue some cork pieces on the back and then silicone the rest and used coco cradle from josh's frogs to cover the back wall and the sides.
 

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I siliconed in a section of light diffuser across my background and I haven't had any issues.

Sorry, I don't have any great advice for you for this time, but that worked for me on a really big, heavy background (36"x36" and includes lots of hardwood jutting out into the tank)
 

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Try thinner layers of GS. I also see more people have this problem with the black pond great stuff than the regular yellow 'gaps and cracks' GS. I've made quite a few vivs with the yellow stuff, both silicone and non-siliconed backs, and have never had a problem, but I always do multiple thin layers and let it fully cure before adding the next layer. YMMV.
 

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Discussion Starter · #6 ·
Jerry Acuff of Planet Aquariums may have found the smoking gun when he inquired further on the specific type of Silicone.

Yes, I had used 100% Silicone, Black. Specifically, DAP, Window Siding and Door. He pointed me to the "fine print", something I hadn't noticed. At the end of the product details, it notes; "Not Paintable".

And THAT could well explain why things like Great Stuff Pond & Stone failed to fully adhere to it. Now, I did hit one of the two problem tanks with standard Great Stuff and did NOT have the same adhesion problem.

So...is it the unique combination of DAP + GS P&S that failed? I can't say for certain yet, but since I have a third tank already set up with the DAP on the background, and lots of standard Great Stuff, It's going to get another attempt...
 

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Try thinner layers of GS. I also see more people have this problem with the black pond great stuff than the regular yellow 'gaps and cracks' GS. I've made quite a few vivs with the yellow stuff, both silicone and non-siliconed backs, and have never had a problem, but I always do multiple thin layers and let it fully cure before adding the next layer. YMMV.

mine was the yellow GS but my problem may have been too much at one time
 

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Jerry Acuff of Planet Aquariums may have found the smoking gun when he inquired further on the specific type of Silicone.

Yes, I had used 100% Silicone, Black. Specifically, DAP, Window Siding and Door. He pointed me to the "fine print", something I hadn't noticed. At the end of the product details, it notes; "Not Paintable".

And THAT could well explain why things like Great Stuff Pond & Stone failed to fully adhere to it. Now, I did hit one of the two problem tanks with standard Great Stuff and did NOT have the same adhesion problem.

So...is it the unique combination of DAP + GS P&S that failed? I can't say for certain yet, but since I have a third tank already set up with the DAP on the background, and lots of standard Great Stuff, It's going to get another attempt...
Nothing really likes to stick to silicon. I honestly can't get my head around this practice of applying a silicon layer in the first place (silicon is used to make molds for epoxy because nothing sticks to it! Even epoxy!). Bear in mind that GS is essentially an expanding polyurethane glue. As long as you're making a second attempt, why not save your silicon, & spread a thin layer of regular Gorilla Glue (polyurethane glue) to the glass instead, give a light mist, allow to cure for a few hours. This way, you have a high density, polyurethane glue, with 100% glass contact (as opposed to low density, foam bubbles), that you can then foam over. I guarantee you that GS will not/ can not/ never ever separate from the gorilla glue. If you wanna absolutely over-kill bullet proof it, apply a second layer of Gorilla Glue, light mist, then GS immediately after, that is, before the glue has had any time to cure. The GS will mix with the Gorilla Glue, and become one with it- more than just a bond.
 

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Nothing really likes to stick to silicon. I honestly can't get my head around this practice of applying a silicon layer in the first place (silicon is used to make molds for epoxy because nothing sticks to it! Even epoxy!). Bear in mind that GS is essentially an expanding polyurethane glue. As long as you're making a second attempt, why not save your silicon, & spread a thin layer of regular Gorilla Glue (polyurethane glue) to the glass instead, give a light mist, allow to cure for a few hours. This way, you have a high density, polyurethane glue, with 100% glass contact (as opposed to low density, foam bubbles), that you can then foam over. I guarantee you that GS will not/ can not/ never ever separate from the gorilla glue. If you wanna absolutely over-kill bullet proof it, apply a second layer of Gorilla Glue, light mist, then GS immediately after, that is, before the glue has had any time to cure. The GS will mix with the Gorilla Glue, and become one with it- more than just a bond.
As you said, it is basically the same thing, polyurethane, but are there any "extra" ingredients in Gorilla Glue that would cause it to remain toxic to plants/animals even after it has cured? I've never used Gorilla Glue in a viv or aquarium, so I am just curious.
 

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I've used Gorilla Glue (the polyurethane one) to mount plants in vivs. Never had any obvious problems.

Regarding GS to silicone... Yeah, nothing sticks to cured silicone. Here's my recipe for polyurethane backgrounds:

Using silicone, attach fiberglass screen to the backs/side. DO NOT cover all the glass with the silicone. Just the top, bottom, and some spots in the middle. You're suspending the screen, not completely embedding it.

Once that cures, you can polyurethane onto the screen and it will lock tight.
 

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I don't use much GS anymore. I like cork mosaics a lot better.

However...

What I have had luck with in the past is NOT using the pond (blackish) GS (like TaratulaGuy said). Use the yellow stuff. I never put anything on the glass prior to using the GS. What I have done is to silicone wood pieces sticking out into the tank directly to the glass and let dry. Then, I come back and put a thin layer of GS around the wood that is stuck to the glass. Then, the GS sticks to the wood, which is anchored to the glass by the silicone. This combination has worked well for me in the past. Really, though, I think most of my success can be attributed to using the regular yellow GS rather than the pond stuff. Not too thick, too. It just doesn't dry well inside if it's too thick. Also, it doesn't hurt to spray the drying GS with water. It reduces drying time at bare minimum but it also my help dry the interior. That's been my experience, anyway.

Best of luck,

Mark
 
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