# Spray Foam Background - Three Questions



## tom855 (Sep 22, 2014)

There is so much info out there on builds, but I had two things I'm still confused about. 

1) Is it safe to assume that Great Stuff foam will hold cork slabs to the back of the tank properly? I've seen a lot of reference to using silicone caulk, but these slabs are slightly arced, and quite frankly they wouldn't provide much surface area for something like caulk. Will spray foam provide the proper adhesion so these things stay fastened against the back wall?

2) When this foam expands, it's likely going to expand onto the side walls. I certainly don't want to see that when I look at the sides of the tank so I assume when I do my trimming I just make a "trench" along the sides of the tank and then fill the "trench" with the same material I'm covering the foam with? Is that the right approach? I'm not sure how else to keep the sides from showing the nasty yellow foam.

3) Finally, knowing that there will be upwards of 4" of gravel, ABG, moss, etc, do I want my cork slabs going all the way to the bottom of the tank, or should I try to keep them above the water line? I didn't know if in general you would want the water to constantly sit against the foam/bark, or if it would be better to keep it above the water line. 

Thanks very much for the advice. This place is incredible.

Tom


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## CosmicFool (Jul 9, 2014)

1 great stuff is pretty strong and will probably hold your cork slabs but it sometimes pulls away from glass so you may still wish to silicone them in the best you can

2 yes it will expand onto the sides of the tank, I recommend pond and stone great stuff because it's black

3 I keep my background above my false bottom/drainage layer but the substrate layer covers it a bit


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## brosta (Oct 25, 2011)

Hey Tom-
The great stuff should hold the cork slabs to the back of the tank. I put the silicone on the glass before the great stuff and that covered the glass so you couldn't see the yellow foam, as well as helping to make sure that the great stuff had good adhesion to the glass & didn't pull away from the glass. 

I have seen tanks that have gone with just the great stuff on the glass and were fine, but I like that added security to make sure. Some of the edges on my first tank didn't have the silicone all the way up to the edge and they stared to pull away, not a big deal, I just filled them with sphagnum moss so the frogs couldn't get back there.

Another alternative would be to put some contact paper on the outside of the glass so you can't see the foam. 

I would try to keep the cork slabs & great stuff above the water line. I am not sure if there is any reason you couldn't have it all the way down, but I just don't like the idea of the water wicking up my background, I would rather be able to control how much water it gets.


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## tom855 (Sep 22, 2014)

Thanks for the great advice. I really appreciate it.

Time to get building!


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## Boondoggle (Dec 9, 2007)

1. I've had spray foam occasionally detach from raw glass. I put a coat of black silicon on the glass first now. It may not do much to hold the arched cork, but it will help hold the spray foam that will hold the arched cork. Also, bust up that cork a bit. It will arch less, taking up less tank room, and if done right actually looks better with veins of mossy peat poking through.

2. It will expand into the side walls...more than you think. I've seen tanks get cracked with expansion, so go easy. I coat the back 5 inches of each side with silicone and then scrape back the silicone after the spray foam is cured. BTW as the spray foam cures it will shrink back a bit so it's nice to have the silicone on the sides for it to adhere to. Lately, though, I just spend the extra money and get the black pond spray foam. It's much more forgiving when your construction medium isn't day-glo yellow.

3. It's not necessary to keep the bark out of the water, but it's better to. You payed for the bark so don't bury it. Figure out your soil depth and then just build from there.

4. You didn't ask these next questions but pretend you did. If you are not going to install a drain then build some tubing for a siphon in behind your background. If (when) you need to drain that thing you will be glad. Also, a lot of new builders, myself included, built there first few tanks with a background that's too thick. Most people first throw up an inch of foam and then build on top of that. Every inch you take with the background takes away from tank space. Remember, all you really have to do is break up that flat surface a bit. Think about actually increasing usable areas with your background as opposed to just covering the glass. Small platforms, voids, areas of just silicone over glass, or even just bare glass can look awesome and increase room to roam. Some of the most realistic looking tanks I have happened because I used spray foam sparingly but thought it out first. Finally, some advice I never seem take myself...take pictures all along the way. I get so excited that I just plow through and never remember to photograph the process, but it can be very helpful for others, and build journals are fun.

Good Luck!


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## tom855 (Sep 22, 2014)

That's just fantastic advice. I have ordered the black foam, along with some black silicon. And FWIW, I will take pictures along the way.

Thanks again!

Tom


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