Building a Giant Plywood Tank
Building a Giant Plywood Tank
Written by Monday, 08 November 2004 00:00
I received many additional questions (many thanks for that) about building a plywood tank since this article is online. After getting more experience with this kind of material, I wanted to change my intro text though, mainly because my initial enthusiasm has faded a bit. YES these tanks cost less, and YES they weigh less, but the first point is rather relative, as a sub 1000L glass tank won't break your bank account. What's more in my opinion, is that the aquarium as such only represents a tiny piece of the total cost to get it up and running as it should, with all fish, filter & lightning included! The weight argument is also of minor importance with a permanent tank. So what remains of the enthusiasm? If you're rather handy, this DIY project can give much satisfaction and joy if it's done right. I also hear you readers coming... am I going to build more plywood tanks? YES I'm indeed going to build more plywood tanks, but this time I won't use precoated plywood, as I discovered that the waterproof layer turns out to be the weak link. Punctures occur very easily, as the mechanical resistance of the protective layer is very poor. My next tanks will be made of bare plywood, covered with a strong polyester - fiberglass coating. This will guarantee a rock solid and a 100% leak free construction that will last for a very long time! Still I feel that the actual article should remain online unaltered, and when I decide to make another plywood tank I'll simply write another article about that project!
What kind of plywood did I use? Instead of using ordinary plywood that has to be coated with polyester/fiberglass or epoxy after assembling, I applied precoated plywood that is commonly used in the building industry for framing reinforced concrete beams, columns, ceilings, ... as the smooth waterproof dark brown phenolic film coating rejects all materials. Even glues and silicones don't attach to it, unless the contact surface is sanded. The best quality boards come from Finnish manufacturers, who produce a wide range from *weather resistant* boards (film thickness 120g/m²) till *wear resistant* boards (film thickness 400g/m²) These boards come in various sizes and thickness: 1250/1500 x 2500/3000mm are the most common boards available in wood shops and 18 - 21mm thickness is also a good size for making tanks. Of course it's obvious that the boards with the thickest film are the best ones for *aquatic* use. More info can be found on the website of a specific Finnish manufacturer. For more information on the availability of such plywood boards you can best contact your local wood shop. Also compare prices as you'd probably don't want to pay more on a plywood tank than on a glass one!
Good screws 5mm x 60mm or 80mm and polymer sealant are used to mount the boards together.
After buying the boards with the correct dimensions in the lumberyard, it's time to do some preparations. The contact surface needs to be sanded a little bit wider as the thickness of the board, and degreased thoroughly to ensure a good adhesive strength. Take care not to sand off too much of the resin, as this exposes the bare wood. In contrary to glass tanks, the silicones used for building plywood tanks serve more as a watertight joint instead of a glue joint. The real strength comes from long screws. The holes, with a maximal distance of 10cm and 5 cm out of the edges, need to be predrilled to prevent damages to the board. Be sure to use a comfortable electric drill that enables you to dose force accurately. Take some remainders to become accustomed to the assemblage of such a tank, as this prevents you to have to buy new boards after messing everything up.
Of course we put silicones between the wood boards before we start screwing. Start with the bottom, then back, sides and finally the front, and be sure to mount all sides against, and not on the bottom board. The smallest bit of logical thinking will prevent many errors. Glue the parts that are going to be assembled only a few minutes in advance. Then start screwing gently while you watch out that no board moves. After the first screw, an error still can be corrected by removing it and start on another hole, but if you discover you didn't work equally in the end, you can start all over again with new boards. Use the silicones sparingly, as all excess material that comes out of the joints needs to be removed, what is a real messy and sticky job. When it's applied in a correct quantity, the excess of silicones can be spread in the inner corners of the tank with a wet fingertip to serve as an extra leak protection.
Plywood strips as a front normally are sufficient to keep the front window in place, but I used a stainless steel frame for the front window, as this aquarium is also a test case for my future 3780L/1000G kitchen tank. The stainless steel frame matches the new kitchen design and it also doesn't rust. Here you see how we've mounted the window. First we spread the 2 tubes of silicones on the frame and then we put the window against the bottom/back without touching the sticky stuff. Slowly we let it come down, so the weight of the glass squeezes the silicones gently to all directions. This way we get a huge contact surface and we don't have to be afraid the window will ever collapse. Before we can add water we also need to mount transverse and length wood strips that will prevent our construction from breaking.
Extra advantages? My Malawi cichlids appreciate the non-reflective dark sides, back and bottom as they feel more relaxed with it, compared to the reflective surfaces of most glass tanks with only the back covered at best. A bare bottom plywood hospital tank is also better for the same reason. Large holes can easily be cut to mount plumbing and filters. Extra accessories like filter hose clips can easily be attached on the outside of the tank.
BEWARE: The same precaution has to be taken to prevent damages to the bottom board as with glass tank bottoms. Not that a plywood bottom will break, but the resin layer can be damaged by sharp rocks, what can cause leaks in the long term. Maybe it's the first time you read this, but that's why we normally place rocks on thin Styrofoam plates.
So far there are still some unanswered questions. As I assembled another (smaller) grow-out tank with this material and the remains of the 3000L/800G tank window, this was the opportunity to make pictures of each step in the building process, so readers can see the new tank growing bit by bit in this article, that can be seen as an addition to the first article.
The boards are cut on precision machines in the lumberyard. Be sure to make a plan with all boards & strips in advance. A good and simple tool for this is the standard Paint program that comes with most Windows versions. Draw a rectangle corresponding to the size of these boards, and fit in all the pieces. Of course you need to keep in mind that these people can't saw pieces out, but only a straight part off a board, so getting the last bit out of each board won't be possible! - After paying them we can take the boards home to start the preparations.
All the boards need to be predrilled, so the screws will be mounted in a correct way. A hit-or-miss approach will definitely lead to a disappointing result - The panels need to be sanded for a maximal adhesive strength of the polymer based sealant.
The contact surfaces could be sanded manually, but I prefer a small electric corner sander. Don't ever use a belt sander, as this damages the waterproof resin layer very rapidly! - A caliper can be used to mark the right distances for the holes that need to be predrilled: 9mm from the side with an 18 mm board thickness and about 1 hole every 10 cm are good measures. Drill the holes very gently, as too much pressure can damage the resin layer on the backside of the board!
The tank already in my fish room with both sides screwed to the bottom board. Because the tank doesn't weight too much, it's standing on an old door that forms an even support for correct and easy assembling.
The polymer based sealant has just been put on the side right before the mounting of the back panel - The polymer based sealant coming out of the joints when whe tighten the boards with the screws.We let the excess of sealant dry for some hours, so it can easily be cut off with a kitchen knife. Right after the screwing we spread the material on the inside of the corners with a wet fingertip, so it forms a sealing joint. Also keep some tissues ready to wipe your sticky fingers.
Be sure to use enough silicons, as a shortage cannot be corrected afterwards. I used 1.5 tube for this 80cm x 80cm window, what was just a tiny bit too much!!!
Et voila!!! Completely cycled and holding different Malawi cichlid species that can grow steadily in the 800L/200G grow-out tank.
Photos by the author.
| < Prev | Next > |
|---|