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Grow bed design
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Author:  cathode [ Aug 4th, '15, 15:35 ]
Post subject:  Grow bed design
I've got a roll of 6ft wide Dura-Skrim on order that should be delivered soon... I need to build a grow bed in the mean time. Due to space constraints I can only feasibly fit a 4ft x 8ft long bed. Interior dimensions will be 42" wide by 89" long, 11" deep. I plan on using lava rock (scoria) for the bottom 6 inches, and about 5 inches of pea gravel for the top layer.

The intent is to run this bed as a continuous flood/flow bed. I'll be running the water level in the grow bed about 1ft above the level of my tank so at 1ft of head my pump can move about 1400 GPH. With that flow rate, is water going to be moving too quickly through the grow bed? or not quickly enough?

I'll post up some CAD screenshots in a few minutes...
Author:  cathode [ Aug 4th, '15, 15:54 ]
Post subject:  Re: Grow bed design
Here's some screenshots of the solidworks model. Not 100% and I haven't exploded the assembly yet to show all the components but you should be able to get the idea.

http://imgur.com/a/n03HY

Overall structural design is that the sides carry the load, constructed like large C-channel beams. The bottom has a short enough span that 3/4" plywood and 2x4's, which will be set in joist-hangar brackets, should provide enough support. I could go to 2x6 lumber for the bottom but i'd rather not, to keep cost down.
Author:  cathode [ Aug 10th, '15, 09:27 ]
Post subject:  Re: Grow bed design
Ok, got this thing built over the last few days. Pretty much ready for putting the liner in at this point, got one question left: Should I paint the inside plywood surfaces first? I'm mostly concerned about condensation issues that might damage the plywood over a long time.

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Author:  Charlie [ Aug 10th, '15, 11:13 ]
Post subject:  Re: Grow bed design
Definitely treat the timber. I think from memory I used a sealer/stainer but anything that will assist out in the weather. Don't fuss on fish safe products because any run-off would be so minuscule that it wouldn't hurt.
Author:  Benny [ Aug 10th, '15, 19:34 ]
Post subject:  Re: Grow bed design
The grow bed looks great! Nice work
Author:  Hezzy89 [ Aug 10th, '15, 22:56 ]
Post subject:  Re: Grow bed design
Growbed looks great ,
May I suggest run the linner two or three layers thick and use timber around the top to pin it in place like a photo frame.
Author:  cathode [ Aug 10th, '15, 23:31 ]
Post subject:  Re: Grow bed design
Thanks. I'll use some paint on the inside, probably paint the outside too while I'm at it.

Hezzy: what would the reasoning be for putting more than one layer of liner? The stuff is really expensive, I'd like to avoid wasting it if possible. I'm using 20-mil Dura-Skrim liner. It's supposedly extremely tough stuff.

I'll definitely put a cap around the top through the liner as it folds over the edge. I may even hit the inside edge with my router and a round-over bit, to eliminate the sharp edge.
Author:  cathode [ Aug 11th, '15, 00:03 ]
Post subject:  Re: Grow bed design
By the way, would anyone be interested in plans for this grow bed? I can generate some 2D drawings from my CAD software.
Author:  Hezzy89 [ Aug 11th, '15, 06:42 ]
Post subject:  Re: Grow bed design
It's probably a lot stronger then the stuff I had, but I used pond linner from bunnings to make similar design and the blue metal rocks put holes in it after 6 months,
Just a thought that's all.
But if your using better quality it could be just fine.
Just sharing bad experience.
Author:  dasboot [ Aug 11th, '15, 09:39 ]
Post subject:  Re: Grow bed design
Quote:
I may even hit the inside edge with my router and a round-over bit, to eliminate the sharp edge.
Quote:
..... :thumbright:
Quote:
Thanks. I'll use some paint on the inside, probably paint the outside too while I'm at it.
Quote:
...... :thumbright:
Author:  Colum Black-Byron [ Aug 11th, '15, 10:09 ]
Post subject:  Re: Grow bed design
Hezzy89 wrote:
It's probably a lot stronger then the stuff I had, but I used pond linner from bunnings to make similar design and the blue metal rocks put holes in it after 6 months,
Just a thought that's all.
But if your using better quality it could be just fine.
Just sharing bad experience.


I used the similar pond liner, and had a similar problem. It's not good stuff.

The duraskim is far tougher though.

If you buy more, I can point you towards a few ebay sellers that have the good stuff.
Author:  cathode [ Aug 11th, '15, 10:55 ]
Post subject:  Re: Grow bed design
I got a 6ft x 50ft roll of dura-skrim, 20-mil thick, for $100.59 + $37 shipping. This is enough for me to build quite a few more grow beds.

I think if I do this again I will make it 12ft long instead of 8ft long. I'm pretty sure the design can span 12ft with the weight of the stone and plants and water. You could probably park a car on this thing, but I wasn't taking any chances...

EDIT: Got it from here: http://www.americover.com/20_mil_reinfo ... 4_prd1.htm

Price changed a few dollars since I purchased.
Author:  cathode [ Aug 12th, '15, 11:04 ]
Post subject:  Re: Grow bed design
Update:

Holy **** that dura-skrim is a pain to deal with. I'm really not happy with how it turned out, I may take the liner out and look for something different. Mostly I'm not happy with how the corners turned out, they look like they could leak really easily.

I started filling with water to leak test and to test my structure to ensure it could hold the weight.
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Author:  Colum Black-Byron [ Aug 12th, '15, 11:30 ]
Post subject:  Re: Grow bed design
Unless you cut it in a weird place, it should be fine.

Just fill it before you cut anything, the weight of the water will push it in.
Author:  skeggley [ Aug 12th, '15, 19:59 ]
Post subject:  Re: Grow bed design
Great looking GB cathode, nice work, reminds me of JT's wicking beds.
Looking forward to your members thread system build. :wink:
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