Rafts Troughs Liner and Rocks
The 2” Dow Corning blue board is recommended by Friendly Aquaponics. Dow Blue Board Info
The 1: foam will float lettuce and other plants OK, but not much mechanical strength to support the net pots that the plants grow in. Also even 2” foam will break easily if stressed like lifting a big piece off full of plants, I cut mine into 2 foot by 4 foot or 2 by 2 foot sections.
Two types of Styrofoam, closed cell and open. The 2” Dow Corning blue board is closed cell, IE no water absorption. The open cell will “powder out” into little bubble shaped pieces, as it ages. Think of the older ice chests that work a while and then flake into pieces
Also, watch for food grade properties. Some foam is made with cyanide and I would not want that near my food products.
It had “snap” lines longwise in the foam making it subject to breaking easily. This is how installers break the foam to incremental sizes when they install it on the outside of a house. I painted the snap lines with 3-4 coats of good latex outdoor paint and that seemed to make it stronger.
I contacted Home Depot and Lowes stores and called corporate HQ. No one had Dow blue board in Dallas area. I emailed the Dow Rep and he recommended a few of his “listed” distributors, none had any in stock but one could order by the truck load. One guy at 84 Lumber recommended SSI.
I found Dow Corning Blue Board” 2inch thick insulation in North West Dallas at SSI. They have several locations in TX, LA, and OK. Blue board cost was $1.31/sq ft $41.92 a board, They charge by the square foot and sell 4’x8’ pieces.
2367 Glenda Lane,
Dallas, TX 75229-3318
Friendly AP recommended 8” of water. The deeper the water (more volume) the less it is effected by temp changes. Also root depth could be enhanced as roots on my taller plants get to be 2 foot long or so.
Rafts and tall plants don’t work well together. Plants fall over due to poor mechanical support with the net pot and the raft. I tried building wire cages for taller plants, but the wind blew them over.
Plants that grow long like melons, beans, tomatoes, will suffer from the raft movement unless all the plant is on top of the raft. Ex: water levels change and raft movement causes root stem stress and damage.
Rafts vs Rocks
Rafts systems are great for plants that are broad and not too tall, like lettuce.
Raft systems don’t filter the fish effluent and algae as well as media (rock) based systems do, so plan on adding a mechanical and ideally a biological filter to your raft system, especially in Texas where the strong sun and heat grow Algae so well.
I have found that seeds start better outside the raft system. I use a watering table where I start the seeds in net pots filled with coarse coconut coir fibers or strips of coconut coir matt that has been washed and rolled into spirals 2” tall, then inserted into the net pots. Be sure to cover the seeds so they are in the dark. The watering table allows me to keep all the seedlings stacked together for easy watering. I often put my seedlings into shallow plastic trays and put an inch of AP water in the bottom of the tray.
Rock systems work well with small to tall plants, even tomatoes and melons, just lay the bulk of the plant along the growbeds on the ground, etc. Rocks filter the effluent better than raft systems, especially with worms in the rocks.
Rocks generally require a lot of physical work to sort sizes and to wash so you don’t get dirty fish tank water. I like 1/2” to 3/4” diameter rock sizes as the grow bed media. Be very selective about what you buy so that it does not require sorting and so much washing. Hydroton is ideal but costly. Rock/gravel is cheap and labor intensive. Expanded shale has been used by others and worth investigating. Lava rock has lots of surface area and is light but is sharp and can damage roots and worms from movement. The black lava rock is preferred as the red powders out more; both usually come with a lot of dust and dirt. Both are damaged by a lot of mechanical handling, like using a powered rock washer.
Here is a good picture of large plants in a rock system Murray Hallam
Make sure your trough liner is food grade, Ex: LDPE (Low Density Polyethylene) and Food grade. Don’t use EPDM as it outgases stuff you don’t want in your plants or your stomach. HDPE (High Density Polyethylene) is good but is expensive.
Thickness of 20 mills or more is good. Liners with reinforcement is better, like fiberglass etc. I used the Home Depot pond liner sheets, 11’ by 6’ size I think it was. Their website shows which are LDPM types. Get the part number and look for it at the Store, or just order it on line.
Note: The Home Depot liner works well but is black on both sides, making it very hard to see the bottom of your troughs. Hold out for the with liner, at least for the inside color.
Two kinds of liner Friendly Aquaponics has used successfully are 23-mil P2000 by Inland Plastics Company, and 20-mil DuraSkrim R20WW by Raven Industries.
Quote from FAP newsletter:
“Raven Industries is now selling trough liner in small quantities directly to aquaponics end-users. Their product 20WW is a 20-mil, LDPE, white string-reinforced, plastic sheeting containing UV inhibitors and thermal stabilizers to assure long outdoor life. (LDPE = Low density polyethylene)”
I have heard this is used by several local APers, but make sure of what you are getting. http://www.pondliner.com/category/firestone_epdm_pond_liner
Frank Morgan found another local to Dallas source for the 2″ Dow Square Board, May 22, 2012.
The Site is: http://www.frpshop.com/ and they regularly stock this 2″ board and charge $35.42 per sheet. They are a subsidiary of Southwest Vault Builders and are located at 596 Bennett Ln in Lewisville, Texas.