2000 gal plywood sump

[karimwassef]

Ah... my tank has multiple systems that can surge/flood. My experience is that the sump needs to be large enough to accommodate a complete tank drain with these kinds of systems. The reality is that this is an acquired rule of thumb, not an absolute measure.

Second, I need a very slow flow with the widest possible cross-section to allow the water to fully clear of bubbles. The configuration is such that the "travel" is 8' and the width of the tank is 13'. That means that the water in the sump is moving at 1/3 the highest flow in the DT at 3x the width.

This might seem excessive but this "reciprocal rule of thumb" allows me to do just about anything I want with the water flow and still have a reasonably clear tank.

Sump (1300gal) ~ DT (1600gal) in volume
Sump W (13') ~ DT L (12')
Sump L (8') ~ DT W (8')

I'm also using a large settling filter to extract particulates for re-injection as food...

So you're thinking ...??!?!

These mechanisms don't change the bubbles and particulates in my system. They allow me to control when and where they appear in my DT without compromising two key variables: food (~particulates) and flow (~bubbles).

[Mebeknob]

So if I were you I’d reshape your tanks with the max length being 8’ simply because that’s the length of plywood. Then you don’t have to worry about joints besides those at the corners.

With the way you have it 3/4” plywood with a plywood eurobrace will Work with caution.

What epoxy are you planning on using?


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[karimwassef]

I've used US Composites 635 for years... great stuff

http://www.uscomposites.com/epoxy.html

15 gallons is ~ $600

The tank is 8' long... but 13' wide.

[karimwassef]

also, my DT is 8' x 12' with a plywood floor.

But that's made with 4 layers = 3" thick of overlapping plywood seams. check out the video that walks through the build.

I've done this kind of thing on a smaller scale before:

http://www.reefcentral.com/forums/sh...p#post21034142

I've built a cube 24x24x24 and a plywood sump 72x24x24

[Mebeknob]

From an engineering standpoint, whatever you did that works for a 24” depth tank will Work for the 18” depth tank in theory regardless of length and width


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[karimwassef]

Ok... so wild idea...

What if I used the concrete slab floor and plywood sides?

The floor will already have epoxy on it.

I would use epoxy to glue the sides. The rest stays the same.

The wood to wood butt joint would be replaced with an epoxy (on wood) to epoxy (on slab) joint.

Once the two are attached, I would apply an epoxy filet and a couple more layers over that.

The plywood bottom wasn't really doing anything. It would save ~ $300 in wood and about $100 in epoxy given that I was planning on costing the bottom floor side of the bottom plywood to be fully sealed.

I am giving up flexibility in redesign, but I can probably redesign around that sump:

Also, I am expecting to have to walk into the sump to access the far wall... and even using a fiberglass ladder in it to access the raised fuge... concrete + epoxy directly should be more durable?

[Mebeknob]

Makes sense to me. With that route I’d consider doing block walls so you can sit, step or put stuff on them.

https://m.youtube.com/watch?v=IjikcTxMiak

The only issue I see with this would be cracks. If cracks develop in the concrete floor it will go through to the foundation. Honestly not really a problem, more of something to be aware of.


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[karimwassef]

The wood has more continuous support and should be cheaper.

I've vacillated between concrete block, rebar and concrete, and wood...

Block is heavy and has weaknesses in the joints.
Rebar wall would be very messy and a lot of work.
Wood should be cheap, light and relatively easy.

[karimwassef]

The floor is 18" triple rebar construction... that's why it's so expensive.

With drylok and epoxy, it should be near impregnable?

[45commando]

Originally Posted by karimwassef

I've vacillated between concrete block, rebar and concrete, and wood...
.

Re-bar & concrete got my attention. Have you priced making the entire sump walls with poured concrete & re-bar supports? The re-bar can be epox'd into the existing slab as upright supports & re-wire used to add lateral . You can build the form & pour the concrete in small stages, so you're not purchasing a bunch of plywood for forms, to then be trashed after a single pour. You are also not limited by the lumber dimensions & won't have to employ structural walls as added security. Just wanted to give you another avenue. Best of luck with your build

[karimwassef]

Actually, that's why I went to plywood. If I'm using the wood forms to pour concrete, I can just leave the wood and coat it in epoxy. It's just less work to get the desired result.

I could make smaller pours but concrete already takes a long time to cure and building it continuously should provide the greatest strength, I believe. It's also a lot of perimeter to pour in small sections.

I was never a big fan of wood really. But I have to admit that its strength to weight ratio does make it a very convenient building material. It won't stop a truck - concrete will. But for 99% of the time, it's a lower cost, lighter weight, strong and convenient building material.

Its weakness is its longevity. While rebar and concrete could last 100 years (more), wood would eventually rot, mold, flake, burn, dry, be eaten ... or otherwise disintegrate. Epoxy changes the math though. Fully epoxy encapsulated plywood has the best of both worlds.

It could survive a flood, hurricane- not sure about tornados, earthquakes and fire though

[45commando]

Originally Posted by karimwassef

I could make smaller pours but concrete already takes a long time to cure and building it continuously should provide the greatest strength, I believe.

I understand your choice for all the reasons you stated, but just wondered if you had crunched the numbers. The form could be constructed with 1/4" ply or even hardboard sheet, so long as it is braced.

Concrete can be poured in stages with no loss in strength. The strength comes from the type of concrete & how dry the pour is (drier is stronger)

If you build with ply, have you considered constructing a center brace/ cross braces ( really a tie or ties) to help prevent the side walls bowing out ? A length of small angle iron, a 2x2 or even some PVC pipe would work. HTH

[karimwassef]

I have considered both kinds of bracing actually (see above), but I really need an open space.

I am planning on a 1" square stainless steel tube around the outside perimeter. While it is possible to deflect a 13' stretch of 1" square tubing, I don't believe the force exerted by 20" of water would be sufficient.

On one side!!!
The support is 3/4" plywood + 2x12 beams + 1" square ss + 1/4" epoxy

And in the other corner!!!
Pressure of 20" of water applied over 13' span



Would a eurobrace top make it even more solid? Absolutely! Do I need it? I don't think so.

I can always brace is once I fill it and measure actual deflection...

[karimwassef]

Confession: working with concrete is also much dirtier and might require renting equipment. I also gravitate towards my comfort zone, especially if the cost differential is low.

Have I calculated the full cost including material and time? No
Have I "rule of thumbed it" and considered that the benefits of the alternate way will likely be less than $100 - yup

[45commando]

Very good point: work with what you are more comfortable with. Best of luck & I'll be waiting to see the finished project.

[McPuff]

I like your idea of using the concrete floor and wood sides. Mind you, this is not based on any knowledge or data. :0)

Would you run pipes in the floor to cool/heat the sump?

[karimwassef]

You mean a fresh water or other coolant loop in the concrete?

Could even use copper since it's encased in concrete and epoxy I guess..

I need to think about this. I didn't consider the thermal benefits or penalties of the slab's direct contact... good point.

[karimwassef]

Thinking it through... the large surface allows me to use a large PEX tubing to cool or heat. I think embedding it in the concrete may be an unnecessary complication and maintenance risk? The exception would be using copper lines for a freon loop (compressor, external radiator and fan) to really cool the concrete. But still- expansion/contraction... feels so risky

I do plan on having gas so running hot water would make for a very efficienct heating loop.

Intrinsically though, the current design should keep the slab very cool... the back room is shaded constantly. The sunroom has a false wooden floor that would keep the slab there shaded as well. So with limited radiated energy and being intimately heatsunk to the shaded earth below, it should help "normalize" the temperature... cooler in the summer, warmer in the winter?

The large underground cooling loops will do this even more being at 10' deep. The air loop will cool the air & the saltwater loop will cool the water. The heat exchangers are the buried pipes directly.. no secondary heat exchangers.

[der_wille_zur_macht]

Having the concrete floor as part of the structure and waterproofing of the tank scares me a bit, honestly. It's putting all your eggs in one basket. You basically have no room for issues, there is a single point of failure. If it were me, I'd go with the all-wood construction and just let it sit on the concrete. At the very least, this will allow for any flex or expansion in the wood/epoxy that might be at different rates than the concrete. You're talking about a very large tank - dynamics that don't matter in typically sized tanks are going to be multiplied.

[karimwassef]

True, but it's 18" of concrete with three layers of rebar coated in drylock.

It's basically as watertight as a pool... so not worried about the concrete cracking.

The wood-concrete interface.... that could exhibit different expansion/contraction or at least fatigue the joints over time. But the interface is epoxy so very hard. The weakest link would break first - epoxy or wood?

There are also two kinds of wood. Plywood inside and 2x12 outside. The 2x12s should be very strong in tension. I would expect the plywood to be strong in tension and compression.

Hard to call.

Would the sidewalls made on concrete block be less prone to failure since the expansion coeff should be the same?

[karimwassef]

Is there a precedence like this problem? Don't we use wood studs and beams over concrete floors? Is there relief built in?

[der_wille_zur_macht]

Originally Posted by karimwassef

Don't we use wood studs and beams over concrete floors?

Yes but if the wood shifts a millimeter on the concrete, there aren't thousands of gallons at stake.

When I disassembled my 360g, the weakest link was epoxy bonding to already cured epoxy, even when proper surface prep had happened. It was still strong but that was clearly the weakest part of the entire structure. Your plan revolves around that type of bond in the most critical joint, and it's between dissimilar materials and under changing pressure from all your surges etc. Hence my reservations!

[karimwassef]

Way to strike FUD - fear, uncertainty and doubt



I guess if I want to take advantage of the cool slab without the hassle of forms or rebar, the only remaining option is to use a 3 layer high concrete block wall ~ 24"

[otrips]

Something to think about. If for some reason the wood failed it would likely result in a total blowout. For example the epoxy developed a crack/hole allowing water into the wood causing rot. You might not notice until it's too late due to the epoxy coating hiding it. The epoxy might be tough but your talking about walking, setting up ladders & working in there over a period of years. Now if you went with poured concrete and it started to fail you would be much more likely to notice a crack giving you time to fix the issue before total failure. Think of it as a small swimming pool, would you rather have one made of concrete or plywood? It might not cost as much as you think especially if your having the room built at the same time. Even if it does take longer and cost a bit more, why would you go cheap on the most important part of the entire system? Your ideas/plan might turn out great & likely will. Personally I'd be waking up with nightmares playing through my head, but that's just my own paranoia & I tend to WAY overbuild everything.
Good luck with the build & I can't wait to see what you have in store for the finished system.

[der_wille_zur_macht]

Wood is very forgiving in terms of noticing and solving problems. It tends to fail very slowly. If the wood core gets wet and starts to delaminate, you will get a slowly developing bow in most cases. I've seen wood tanks that had run partially failed for months. I had a local guy who had a tank with a bad leak that damaged the wood and ended up bowing several inches. He fixed the leak and kept running it with the bow. I wouldn't have but there was no catastrophic failure. My own tank had a pinhole underwater allowing water into the eurobrace for months. I lowered the water level an inch so the pinhole was above the water line and kept running it, even with the damaged wood core. A year or so later I drained the tank and ran fiberglass over the damage. The tank ran for several years after that.

I can't speak to personal experience with concrete but I can say wood tanks are very forgiving.