# My DIY cave system



## steviestv8 (Aug 16, 2010)

This is my foam outline for my Malawi tank it is 18" across both back and 18" high it will sit in one of the corners. Now i have a question what is best way to cover it? should i just cement it and soak it for a few weeks or use drylock?


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## DanniGirl (Jan 25, 2007)

Looks good!
I'd go for Drylok- easier to manipulate, IMO.


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## The King Crabb (Jun 28, 2011)

What I'm planning to use when I make my background, which will be in about a month, is this: http://www.homedepot.com/h_d1/N-5yc1v/R ... ogId=10053 I haven't checked out all the stuff it's got in it so you'll have to do that (let me know what is), make sure that it's non-toxic and isn't oil based. You can then mix that (do it in a separate container so if you mess up you don't waste it all) with different colors of non toxic acrylic paint to get the coloration you want on your background and to make it look natural.


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## steviestv8 (Aug 16, 2010)

Thanks guys. Only question then is with the drylok I guess I'm going to have to attach some kind of weight or something to keep it from floating. Any ideas on what to do I'm try to stay away from silicone


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## steviestv8 (Aug 16, 2010)

Thanks guys. Only question then is with the drylok I guess I'm going to have to attach some kind of weight or something to keep it from floating. Any ideas on what to do I'm try to stay away from silicone


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## CrypticLifeStyle (Dec 14, 2009)

If you add real rock to the top should be enough weight to hold it down & maybe on each side of the bottom portion so it dosnt kick-back float up.


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## steviestv8 (Aug 16, 2010)

Thanks guys. Only question then is with the drylok I guess I'm going to have to attach some kind of weight or something to keep it from floating. Any ideas on what to do I'm try to stay away from silicone


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## steviestv8 (Aug 16, 2010)

I was thinking if replace the base tiers with some field stone rocks that have acted as caves for me before ill just have to mix and match to see how heavy I need thanks for the ideas. Also I heard about putting fishing weights in the Styrofoam and covering them with the cement or acrylic sealent


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## Agridion (Sep 8, 2010)

steviestv8 said:


> Thanks guys. Only question then is with the drylok I guess I'm going to have to attach some kind of weight or something to keep it from floating. Any ideas on what to do I'm try to stay away from silicone


I like the looks of your design. You could build the whole thing out of light weight concrete; it's a bunch of work but turns out looking pretty sweet. All of that Styrofoam you are using will take a LOT of weight to hold it down. Say 90 + pounds of dense rock and I wouldn't put the rock on top of the Styrofoam because that would make the structure want to flip over having the buoyant material held down by a heavy material. Good luck. Many people don't realize how buoyant Styrofoam really is... Even a small piece takes quite a bit of a dense material to sink it.


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## steviestv8 (Aug 16, 2010)

This has been bugging me for a little while is there a way to know exactly how much weight the bottom of a tank can hold i know its a good amount over thing is this is only a 40 gallon fry tank that this is going in and i already have 30lbs of sand in it and a full tank so 8.4lbs per gallon x40gallons is about 336lbs so im looking at roughly 366lbs plus if that ends up being a 90lb piece that would put me at about 426lbs, and its a pentagon tank only 18"by 18" along two 90 degree pieces and 3 12" pieces in front for viewing and 24" high. So all the weight is in a smaller area. I know this is alot to read but will this cause any problems for my tank?


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## PfunMo (Jul 30, 2009)

I think you will find you can almost fill a tank with rock and not hurt it. As you add rocks, youe displace water so the net result is not all that bad.

For holding it down, I would consider either a large flat piece of rock or pouring a slab with concrete. Definite advantage to it being on the bottom as mentioned. A hole drilled in rock to run all thread to the top to mount a solid plate, making a snadwich of the foam would be first thought. If one poured a slab, the all thread could be embedded in the pouring.


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## steviestv8 (Aug 16, 2010)

Thanks I forgot about the displacement of the water I.feel kind of dumb now haha. And ill Def am going to create a slab I can hide underneath .I'm gonna cover the whole thing.first and see aprox how much I need


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## The King Crabb (Jun 28, 2011)

Another option you could do is buy some quikrete for $3 and then scrape out some styrofoam and replace it with quikrete. You'd get the same look but it would be heavier.


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## iwade4fish (Jan 5, 2009)

Some use rare-earth magnets to affix the BG to the panes of glass. Silicone them into the styro and....there's a thread on here somewhere about them, use the search feature.

The 'all thread' idea with concrete is a great way to go for a no-silicone adhesion.

And I have 1,200lbs of rock in a 5 foot tank, no problems. Recently dropped an 80lber from about 8 inches; scratched it, but it held!!!!!


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## PfunMo (Jul 30, 2009)

I like silicone in lots of ways but it does have some faults. If you have some silicone around the house and pull on it, it comes loose. When we are talking about whether it will hold a bunch of foam down, we don't have a lot of room for error. If we guess wrong and it turns loose, the background may blow the whole top off the tank! That is where I want to be absolutely sure the background will stay down. All thread is a structural material. Combine it with concrete and you have a real solid anchor.


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