Just finished a long reply concerning plywood tanks...

pleco_farmer · Post by **pleco_farmer** » 19 Dec 2004, 14:25

...I've received several requests, so I thought I might share this long winded reply to a request for plywood tank advice.

3/4" plywood, BC sanded for looks. Marine isn't necessary, if water is penetrating the epoxy then water resistant plywood won't save you. 1/4" dadoes and rabbets on all joints, increase the bonding surfaces and help to align during construction. Be sure that the bottom is cut to the final outer dimensions, the sides need to sit on top of the bottom so outward pressure of water is at right angle to the fasteners. Attach with epxoy and 1 5/8", #8 deck screws, at a minimum of 4" apart using pre-drilled/counter-sunk holes.

At depths up to 24", brace every 24". Keep at least 2" of plywood around openings in braces. Likewise for windows, leave at least 2" around the openings. Radius inside corners to a minimum of 3/4" to reduce stress.

I use West Systems epoxy. This is an amine-cured product which is not FDA approved, but is commonly used to line potable water tanks built into boat bulkheads. The company states that they haven't the need to undergo FDA certification but they post potable water tank projects in their literature, so product is fish-safe. More so than any other technology I have used. I have been using it now for over two years with success.

First coat is applied thin, wetting the wood, sealing the surface. I apply between three and four additional coats, sanding to 150 grit. All joints are reinforced with 2" fiberglass tape. I avoid overlap but mitering the tape after it has been applied and coated, but not quite dry.

Once the tank is coated, I apply wood strips around the top edge. These are rabbeted to accept plexiglass lids, attached with epoxy, then sealed with epoxy.

For windows, I use 1/4" acrylic up to 12" of depth, 3/8" beyond. (That's a max 8"X20" opening for 1/4") Cut plastic to fit the entire span from side to brace, and top to bottom, inside the tank, with a 1/4" gap on all sides. Turn the tank so opening is face down and apply a large bead of silicone sealant around the opening. Drop the acrylic in place and weight it down. Smoothest way to accomplish this is to cut wood strips to match the plywood surrounding the opening, and another piece of plywood about the same size as the acrylic. Place the strips on the acrylic, the plywood over the strips, then the buckets on the plywood. This distributes the weight nicely. The sealant should completely fill the area between the acrylic and the plywood surround. Let any squeeze out dry, it is best trimmed after it has set.

Most important issue is squaring up the tank during construction. Loads must be evenly distributed, and misaligned sides are troublesome. Also, be sure to level the installation for the same reason.

The cost is on a par with glass, but I generally build because glass is not available in sizes that I need. This is not a way to save money on the tank. But, if you need an nine foot long tank, with six eighteen inch compartments, sisxteen inches deep and sixteen inches wide, you aren't going to find it in glass, and all acrylic will be outrageously expensive.

With the West Systems epoxy, I have had a growout tank, 48X30X16, running for two years now, no problems. I drained and inspected it a month ago, and found no cracks, no swelling, no issues at all.

I usually finish the outside with latex paint. A good sanded plywood takes a nice finish. Screw holes are filled with Durham Water Putty prior to painting. I have done a tank where I filled the holes with mahogany plugs then applied a water-based mahogany stain. This was then coated with two light coats of epoxy, sanding to 220, then 400.

To color the interior of the tank, it is best to use an aniline dye stain. West Systems recommends this for greater adhesion. I keep most tanks natural, the epoxy turns out to match a honey maple color. However, my zebra tanks have been stained with a black aniline dye.

Let me know what you are attempting, and I can reply with any relevant experience. It's a fun project, and using the West Systems, you can even do it inside, with decent ventilation. Other products simply gas you out of the room.

For success my best advice:
1. Spend some money on quality materials
2. Spend your time, and be obsessive about details
3. Spend your patience, allowing each step, epoxy and silicone, to fully cure before proceeding to the next.

Post by **Shane** » 19 Dec 2004, 14:58

Can you post some pics of your systems? One pic is worth a thousand words. Also, have you tried the large plastic troughs usually sold as cattle watering troughs or the big fiberglass containers used to ship fruits and vegetables? My Dad has one of the second type that he uses as a water trough for one of his horse pastures. It is about 8 foot by foor foot and actually fairly light. He said they are very cheap to purchase. Looks like it would make a perfect large tank.
-Shane

BK · Post by BK » 19 Dec 2004, 19:30

thanks for the pm and this post.

is the fiber glass absolutly essential? i hate that stuff after using it to build an electric race car body.

i was considering building a ~8ft long ~2ft wide and ~16" high tank to house ~three 4-5" L25 till they get larger. i had planned on epoxying granite or slate tiles over the paint to keep them from rasping it. I was also planning on epoxying a wood triangle (45-90-45) into all interior corners to help strenghten them up. also top braces. the bottom and sides would have a 2x4 screwed to them to hold the plywood ends in (i believe its called ledger strips??) i figure if i incorporated a .5x1" board slotted in the middle on the inside at the right intervals i could slip a piece of egg crate in to section off the tank. the tank wouldn't have any windows and would mainly be just to house them till i get a more permenant residence (easier to move than glass and a proper glass tank can be found. My cousin has given me some ideas as he built a large hot tub from ~1" thick pine instead of ply that has held up quite well considering its usually filled with people who have been drinking

.

A top veiw

Any comments on this idea? think 1" ply would be needed for this tank?

also wondering if you had ever heard of using thinned down silicone painted on a tank to seal it (basically a "rubber" liner).

i had also considered those stock tanks but considered trying to line them with something so the plecs couldn't rasp the plastic to difficult.

shane, any idea where to get those fruit containers?

thanks and sorry for so many questions,
BK

pleco_farmer · Post by **pleco_farmer** » 20 Dec 2004, 00:57

I started out with rubbermaid horse troughs for growing out ancistrus. $50.00 USD for 75 gal., and yes they are lightweight, sturdy, etc...however, mounting accesories to the sides is difficult, since the lip is over an inch wide. The surface was rough, so suction cups inside were a failure as well. I ended up with some vertical sheets of acrylic slotted into an acrylic base to hold heaters, etc...so most problems had workarounds. But, the biggest issue was the fact that the troughs were oval. I was willing to sacrifice some water volume for floor space, but chasing down the fish was a nightmare. I forgot how often one traps a fish against the nice flat glass side of a rectagular tank. When I pull for deliveries, I can bag one hundred plecs from the rectangular tank in one fourth the time as from the trough.

Tips for using the troughs,
...think about pond-type filtration, where the entire unit is submerged.
...I tried a few divider schemes to reduce the tank size when harvesting, these also provided a flat surface to trap fish, but you still have to deal with the rounded ends
...mine had built-in bulkheads which was nice for a drain, but I would usually siphon in order to target waste, so the BH wasn't a real advantage

pleco_farmer · Post by **pleco_farmer** » 20 Dec 2004, 01:14

I've done 108"X24"X16" in 3/4 plywood as described above. The nine foot tank has dividers, front to back, every sixteen inches. This is probably the biggest, and was maybe the fifth tank I had built, starting with 48"X30"X12". I've never done the formal engineering on the loads, but with the dividers, even hollowed out, you are basically building a series of much smaller tanks.

The biggest loads occur at the bottom edges of the tank, where the weight of the water wants to push the sides outward. It is essential to be screwing up through the bottom, into the sides. The fasteners will be perpendicular to the greatest load.

Another way to think about the loads is to imagine a view of the tank from above. A deep rectangular tank filled with water, would like to become a shallow circular tank filled with water. Therefore, without bridging perpendicular to length, long sides have a tendency to bow out. I've never had a problem, but I do not exceed 24" without bridging.

Rasping? Couldn't tell ya'...the only real grazers that I keep in plywood are ancistrus, with no issues. L-177 as well, no problem. Maybe its time to break down and find a nice fat royal, "Honest, it's for an experiment..."

Post by **Shane** » 20 Dec 2004, 03:29

Check out some of these:

96" X 24" X 12" $135
Would be great for Corys or raising loricariids. Price is about 41.00 a gallon.
http://www.aquaticeco.com/index.cfm/fus ... 9/cid/1032

These are what I was talking about.
They offer:

CAPACITY WIDTH LENGTH HEIGHT
140 Gallons 40" 40" 20"
280 Gallons 40" 80" 20"

http://www.loomistank.com/troughs.html

WhitePine · Post by **WhitePine** » 20 Dec 2004, 04:57

you could just get this...
http://www.aquaticeco.com/index.cfm/fus ... 1/cid/1169

I don't know if that fits your needs exactly though...lol

Post by **Shane** » 20 Dec 2004, 13:36

Thanks Justin! I'll have to kepp that link for the Red Tail Catfish folks.
-Shane

pleco_farmer · Post by **pleco_farmer** » 20 Dec 2004, 22:36

Quick snaps for the thread...

First one...48X30X12

From above, covers are removed, but you can see the rabbeted rim. Note the center bracing, and yes, that is a reflection, not an underwater outlet!

An ancistrus, little behind in his work. I did not fully sand the fiberglass tape before coating it again, so it is obvious. With a little more care, you can almost make these disappear. Live and learn.

This is a 189L rubbermaid horse trough. Rigged a Magnum by trimming a bit on the wet wheel, and adding a bit on the fiter support.

Note the dangling heater, and up and coming anubias...140W of daylight bulbs keep the algae going. Even so, 200 odd bushies will occasionally clean it up entirely

BK · Post by BK » 21 Dec 2004, 00:09

are you using a seperate piece of acryllic for each window? if so i have some acryllic and polycarb scraps thast just may fit the bill

, still rather use glass though.

what type of fiberglass tape are you using? and are you just using the epoxy paint to apply it?

also wondering if you had ever heard of using sikaflex for attatching/sealing the window. i have read it sticks better to acryllic than silicone and that a tube goes quite a ways.

thanks

pleco_farmer · Post by **pleco_farmer** » 21 Dec 2004, 00:50

Its not an epoxy paint, I use a two part, epoxy/hardener, product. The tape is typical fiberglass fabric, easily found in marine shops, or auto parts stores.

I usually use acrylic since I can machine it more easily than glass, and it is generally safer to store stock in the shop. Too much breakage/waste with glass. Each panel is a single sheet of arylic cut slightly smaller than than face of the tank between the side and divider.

As far as silcone is concerned, I work with what works. I've used sikaflex in boat construction, its a good product, especially under marine conditions, but costs over twice as much as silicone. Both are aquarium-safe. It just not that demanding an application.

I gone through about 500 sq ft of acrylic in the shop across a variety of projects, and unless a piece gets up to around 2'X4', I haven't paid for any of it. Find a local plastics dealer and scrounge scrap bins. Typically, they charge by the pound, but the counter guys usually let me walk, not wanting to write up invoices for $3.00 in cutoffs. They also put me onto an NSF approved silicone for $3.00/10 oz tube.

Mika · Post by **Mika** » 21 Dec 2004, 05:34

http://home.online.no/~joobjoer/eng_diy ... itres.html