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Grow bed construction
The 4'x8' growing bed with side made out of 2x12" and a bottom of 3/4" cdx plywood and coated them with cloth, 6 coats of Elasto-seal and 2 coats of snow-roof. The 2 x 12 sides are glued together with a water proof glue and screwed with 3" screws. The bottom is glued and screwed to the sides with 2" screws 2" on center.
The Lumber and Elasto-seal came from Home depot. http://www.homedepot.com/home.html
You could use a
plastic liner to seal the beds.
Th drain was made by drilling a hole in the bottom of the bed
that a 2" to 1 1/2" bushing would fit tight in. The
bushing was pushed through the hole and sealed with silicons
rubber sealant. Then a 2" 90 was glued to the bushing on the
bottom and sealed with silicons rubber sealant. Another 1
1/2" bushing was glued into the other end of the 90. Next a
piece of 1 1/2" pipe long enough to extent past the end of
the bed with a thread adapter was glued into the bushing. A 1
1/2" ball valve was screwed onto the thread adapter. A piece
of 1 1/2" pipe long enough to reach over rhe fish tank with
thread adapters on each end was screwed in to the ball valve and
a threaded cap with 1/8" holes drilled in it so it would
work lik a shower heat was screwed on the end. A pice of
1 1/2" pipe long enougth to raise 2" above the bed was
cut and drilled full of 3/16" holes for the stand pipe and
put in the bushind in the bottom of the bed.( do not glue the
stand pipe!)
In the bottom of the bed I put a frame of five 3/4" plastic pipe hooked together at one end with a riser comming to the top so I could flush the bed. the other ends were caped. 3/16" holes were drillde in the sides.
On top of this frame work I put 2 foot X 4 foot plastic egg crate like that is used for fluorescent lights, over that I put plastic fly screen. Then I filled the bed with gravel.
On top of the gravel I put a water distribution system made out of 1" plastic pipe which is a frame around all four sides with five cross pipes. The water comes in a center pipe 10" above the frame and tied to the distribution system at each end and in the center. A 1" to 3/4" bushing is in the inlet and a 12" piece of 3/4" plastic pipe is glued in it. I use a pirce of 1" clear plastic tubing to conect it to the pump manifold so I can see when it needs cleaning. There is a ball valve on the manifold to control the water flow in and the ball valve on the drain line controls thr flow out.
You can use the bed without the 3/4" frame, egg crate and fly screen but the fine particles clog the bed in time. When I flush the bed I change the drain pipe so that it goes into me filters.