WARNING! There has been discussion among attendees of our courses about alternatives to the Styrofoam rafts we use (which were approved for organic certification by Oregon Tilth), and some of this discussion involved using plywood for rafts or portions of rafts in the troughs. Exterior plywood is glued with a urea-based formaldehyde-containing glue that is a known toxic material. Even if your organic certifying agency doesn’t catch this item, it will still leach off into the troughs and possibly kill or stunt your fish and vegetables. Even if it doesn’t, you will be feeding formaldehyde to someone down the food chain. IF you decide to use INTERIOR-grade plywood, because it’s NOT glued with the toxic glue, your interior plywood will degrade and FALL APART under exposure to moisture because it’s not designed to get wet! Use the Styrofoam rafts, they’re food-grade just like a coffee cup.
(Below) An awesome premanufactured raft by Randy Campbell, of Today’s Green Acres in Elora, Tennessee (email Randy about rafts by clicking here).
We use 2” Dow Blue Board Styrofoam “Square Edge” rafts for our aquaponics, and have had NO problems with them. This Blue Board comes in several OTHER configurations which do not work as well: one is called “Tongue and Groove” Blue Board, this is OK, but has a bump on one edge and a groove on the other which make them difficult to paint and also make the edges of the rafts more vulnerable to damage. Another type of Blue Board is called “ScoreBoard”, and this one is a pain because it has three scores down the long 8’ dimension of the sheet that are designed to help the sheet BREAK EASILY along these scores. It works: they DO break easily along these scores, when you are harvesting, planting, or just looking at them crossways. DON’T get “Score Board” unless you have no other choice, and then, cut your 2X4 rafts out crossways, with the cut lines going across the “Score” lines, not parallel to them! How do we know? 🙁
(Below) Making our own rafts out of 2″ Dow Blue Board; Tim is drilling through a 1/4-inch plywood template that makes getting the holes perfect EASY.
There’s another brand of raft foam; this is Owens Corning “Foamular”; it’s pink. Unfortunately, Owens Corning changed the “blowing agent” that makes the little bubbles in the foam in early 2013 to something the State of California considers potentially carcinogenic; so this foam is no longer an option, and is not certifiable by the organic certifying agencies.
If you can’t find Dow Blue Board, you can use that white styrofoam that looks like a bunch of little beads stuck together; it is food grade, just like a styrofoam coffee cup, but it is much weaker than the Blue Board. Cut it into 2 foot by 2 foot rafts, and it will last a lot longer than trying to put all the weight of mature vegetables on a 2 by 4 raft of this stuff.
WARNING! Do not be tempted to make your troughs a little narrower so the 48-inch wide raft will fit “snugly”. Some of our students came up with this idea on their own to prevent any algae from growing around the edges of the raft/trough space, and as a result, have created other problems for themselves. Here’s why:
First, the algae is not a problem. There is a very small amount of algae involved; it simply means you will always have a fringe of algae on the trough liner at the waterline, and on the raft itself. These are dynamic ecosystems, and this is OK; it’s how they operate! The mosquito fish and Gammarus will dine on the algae and add more nutrients to the system as a result.
In addition, you’re going to have a 1” PVC airline floating on one side of the raft in each trough, which is 1-1/4” diameter, leaving 1-3/4” of clearance for the raft. The trough itself, because of vagaries in the installation process (such as big rocks that you are trying to pound a 5/8” form stake THROUGH, which will make the form stake lean in or out instead of going straight up and down), will vary in width. It will be wider at points, and narrower at other points from the 51” inside dimension shown on the construction plans. Also, one of the main benefits of raft aquaponics is that the rafts float EASILY from one end of the trough to the other. A raft that fits snugly eliminates this benefit and will cause you hundreds of hours more work during the lifetime of that system.
WARNING! We have just been informed that the Benjamin Moore Semigloss Exterior Acrylic Latex Enamel, color “Brilliant White”, that we have been recommending for so long has now had mildewcide added to it, and the mildewcide is NOT listed on the paint can label! We do not have an “approved” new paint to recommend; this will have to be approved by your Organic Certification agency, and anything we could say about it would just be an opinion. But. What you need is a good quality latex semi-gloss exterior enamel with NO mildewcide in it. Try the paint out on your Micro System first, and get an approval letter from your organic certification agency for the paint you’ve selected.
WARNING: Do NOT use paint with mildewcide in it!!! This is a form of poison that is added to paint to keep mildew and mold from growing on your nicely painted surfaces. The poison will leach out into your water and kill your fish and plants! Make sure your paint does not have mildewcide in it!
WARNING! ALSO DO NOT use pink or white Polyisocyanurate foam rafts if you find them. These are often available the same places the Blue Board is, and are cheaper. Does “cyanurate” sound like “cyanide” to you? It is a related chemical compound and it is toxic; we have a report of one aquaponicist using it, and although his fish had been fine in the system for a month or so, approximately one-tenth of his fish died the week after he put the rafts in the system. We don’t know if the rafts were causal here, do you want to experiment and find out? They’re also NOT organically certifiable!