Grow bed design for raft system

[Pat Moore]

Aloha, I posted the following to the comments section and then realized it should have been posted as a discussion topic.  Any advice will be most appreciated...

I am in the designing phase for building two grow beds for a raft system.  The rafts need to be elevated about 3 ft off of the ground for accessibility.  I took the Friendly 3 day course and have their manual, but the only use ground mounted beds.  I would like to use 3/4" 4x8 plywood for the bottoms and sides.  However, the Friendly beds were 51" wide so that they could fully use 48" Dow blue board with some room to spare for easy movement.  Does anyone see any issues with cutting down the blue board to approximately 46" other than some loss of area?  Also, instead of using a food grade liner I'm thinking of using glass cloth and epoxy for waterproofing the beds and would like to know if this is a good or bad idea.  I'm new to the forum and excited to be part of the community...

[Rob Nash]

Pat, welcome to the community, its a great place to hash out some ideas before going all in...

theres no problem cutting the boards down to fit inside the beds. i would use 2"x12" for the sides, screw 1-1/2" deck screws from the bottom, every 8"  and 3" deck screws on the corners(no more than 3 screws). i have one like this thats 4' x16' and has held up for 3 yrs. ...ive heard mixed reviews on fiberglass, i think its all in the choice of resin you use.

now the friendlys dont use media... are you planning on doing all the separator and bio filters, de gassers, etc? ...or just pump strait into the plant roots in the raft, like they advise on the micro system?

...i recommend you do a hybrid system, using media beds for the filtration, then go to the rafts.

[Jon Parr]

Hi Pat. I think fiberglass would be great, and personally I would use the two part epoxy rather than polyester resin. However, the duraskrim that Friendly's uses is hard to beat, only $200 per 100' roll delivered to my doorstep. And the lack of stretch and Friendly's style of NOT folding the duraskrim into the bottom corners goes a long way to get solid beds with less structure, as gravity holds the sides from bowing under the lateral push of water. Also, you might consider rafts that are elevated above the water an inch or two, as growth results may improve and need for aeration will lessen. And if they don't need to float, then you are not married to styrofoam. Just some options to muddy the waters for you :D

[Pat Moore]

Jon and Rob,

Thanks for the responses.  I should clarify that the grow beds are what I need to have raised off the ground about 3 feet so bending over is reduced to a minimum.  I'll have to price the duraskrim  here in Hawaii and compare it to using epoxy and fiberglass.  I have done a bit of fiberglass work but have never used the duraskrim but am willing to give it a go.  Using 2"x12" is a good suggestion Rob and I think that will work fine.  I was just planning on following the Friendly micro system setup with minimal filtration but would be interested in finding out more about designing a hybrid system as you suggest. Have you done one and do you have any suggested links for additional information? 

Rob Nash said:

Pat, welcome to the community, its a great place to hash out some ideas before going all in...

theres no problem cutting the boards down to fit inside the beds. i would use 2"x12" for the sides, screw 1-1/2" deck screws from the bottom, every 8"  and 3" deck screws on the corners(no more than 3 screws). i have one like this thats 4' x16' and has held up for 3 yrs. ...ive heard mixed reviews on fiberglass, i think its all in the choice of resin you use.

now the friendlys dont use media... are you planning on doing all the separator and bio filters, de gassers, etc? ...or just pump strait into the plant roots in the raft, like they advise on the micro system?

...i recommend you do a hybrid system, using media beds for the filtration, then go to the rafts.