# Expanding foam and silicone adhesion



## RationalRobots (Jan 3, 2017)

Hello all,

This is my first post here... so be gentle!

So for the past few months I've been collecting materials and spending a vast amount of time researching to build a naturalistic, bio active terrarium (using an exo terra 60x45x60) to house a group of 3 red eyes. 
I aim to get them in roughly a month ... but as I'm starting the build now, and they'll be going into a quarantine tank for 4-6 weeks, I have plenty of time for the build... so I want to do it right the first time so it will last for as long as possible.

So on to my question... 
I want to use the standard GS method to add some texture to the whole back and right side of the tank, with a little on the left... but I want to do it without taking too much space away from the frogs.

For the foam I have 'Touch n Foam black Waterfall foam' ... seems like the safest option I could find.
And for the silicone I've gone with 'Bond-It HA6 Marine' aquarium silicone - I've got brown for bonding the coco to the foam, black to go on the inside of the glass behind the foam ( to make it look less messy from the back of the tank), and clear to improve the exo terra door seals and vents.

I've been doing some small scale tests and have found that the foam really doesn't adhear well to the cured silicone... a slight tug when cured brings it cleanly apart? so I need a better way of getting everything to stick:

I did another test and found that applying the foam directly onto a layer of un-cured silicone worked well? but this may lead to the silicone not curing fully? so I won?t do this.
I've got some extra egg crate left over from the false bottom ( I couldn?t actually find this in the UK so I?ve gone with plastic grid for coral aquariums ? very sturdy stuff ) that I could press into the black silicone on the glass before foaming, but I'm wondering how much I need to use, and what the best placement is? Do I just need some 'strips' along the edges, with some small bits dotted in the middle, or should I use a whole sheet to cover the whole back?

Or does anyone have any other suggestions.

Many thanks,
Chris


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## Keni (Feb 1, 2017)

I'm not sure ew hat your plan is exactly with the silicone behind the foam. If it's spray foam then it will stick to the glass on its own and the seams where there is silicone won't cause a problem for the rest to hold in place.


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## TheForSaken (Nov 21, 2016)

You could also use black contact paper on the back of your viv to make for a much cleaner look. 
Would save ya a ton of silicone and wouldn't be wasting time smearing it all over the back glass.


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## Pumilo (Sep 4, 2010)

Black foam is crap. It does not adhere properly to glass or silicone. There are multiple stories about it failing completely and having a whole wall end up on their viv floor. I happened to me once. 
Straight up, black foam does NOT adhere as well as the normal, yellowish-tan foam.


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## serial hobbiest (Mar 5, 2017)

Yeah, if you want to make a mold for polyurethane foam, make it from RTV silicone. Polyurethane will not bond to cured silicone, and silicone only kinda sorta bonds with cured polyurethane, which is why you gotta carve all that polyurethane to expose the gas pockets to vastly increase the surface area before applying your background material. That being said you'll find lots of people who'll apply the foam right over top freshly laid silicone. I really don't know if that's a good idea or not, but I intend to test this idea when I do my first build.

Bonding eggcrate to the glass first sounds like the strongest option, although I question how necessary it is. Unless you intend to support a great deal of weight, I wouldn't bother. Silicone will bond to the glass better than it will to the egg crate, I would think. If you go this route, be sure to leave lots of glass bare when you silicone your egg crate in place, so you get benefit of the foam anchoring to the glass as well, so you're not completely relying on your silicone bond with the egg crate. And since you're going through the trouble anyhow, you'll always improve a bond by roughing up the surface with coarse sandpaper first.

Another idea is to simply drizzle polyurethane glue (Gorilla Glue) on the glass before foaming over it. The foam is merely low density polyurethane glue after all. Because the glue is denser than the foam, you'll have a stronger bond with the glass than foam alone.

Whatever you do, just be sure to clean the glass with alcohol first, and remember that polyurethane adhesives require humidity to cure.


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## FrogSnob (Feb 4, 2013)

Pumilo is right. Stay away from black foam and I have had yellow foam fail as well (twice) when I sprayed it directly to the glass.


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## Gibbs.JP (Feb 16, 2016)

Keni said:


> I'm not sure ew hat your plan is exactly with the silicone behind the foam. If it's spray foam then it will stick to the glass on its own and the seams where there is silicone won't cause a problem for the rest to hold in place.


Not true about foam directly on glass. As the others have said above, it has been (very often) proven to detach from the glass. I tore apart a tank that I used black foam right on glass, and was surprised just how easy I was able to tear it off.

What I do (and many others) is apply black silicone to the glass and then use the yellow spray foam over that. The foam adheres better to the silicone, and you have a nice, solid black finish inside the glass to hide all the ugly foam.


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## serial hobbiest (Mar 5, 2017)

Gibbs.JP said:


> Not true about foam directly on glass. As the others have said above, it has been (very often) proven to detach from the glass. I tore apart a tank that I used black foam right on glass, and was surprised just how easy I was able to tear it off.
> 
> What I do (and many others) is apply black silicone to the glass and then use the yellow spray foam over that. The foam adheres better to the silicone, and you have a nice, solid black finish inside the glass to hide all the ugly foam.


To clarify, you're foaming over top the silicone immediately after applying it, is that correct?


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## Gibbs.JP (Feb 16, 2016)

serial hobbiest said:


> To clarify, you're foaming over top the silicone immediately after applying it, is that correct?


No. Let the silicone cure first and then foam over the cured silicone.


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