polypropylene for "tray-ponics"-type "rafts"

[Paul Trudeau]

Glenn Martinez has described a nice small raft system where he uses 24 inch x 36 inch x 8 inch-deep plastic masonry mixing tubs (trays) (available at Home Depot) as plant troughs.  Instead of floating foam rafts, he lays a 24 inch x 36 inch piece of plywood on the top edge of the tray, an inch or two above the water level.  I built my system last year on this model.  As he did, I stained the plywood with some white stain.  It's worked OK for me, but I've had a few problems with the plywood:

(1) fairly labor-intensive to drill and stain

(2) warping

(3) not easy to clean plant debris, mold, or algae off the stained wood

The morning after the US election in November, I collected as many plastic campaign lawn signs as I could find and have been experimenting with using them instead of plywood.  They are made of 4 mm corrugated (aka "fluted") polypropylene (same material used in a number of food packaging items yogurt cups).  Some of these signs are exactly 1/2 the size of one of those masonry trays, so two of the signs cover one tray perfectly.  Each half is supported on 3 of its 4 edges by the rim of the tray.  The 4th edge needs a little support in the middle, so I use a 7 inch scrap of PVC pipe standing on end in the tray.  So far it's working out great.  These re-purposed signs do of course have printing on them, and I'm finding that the printing can scrape off.  So I'm planning to buy sheets of new (unpainted) corrugated polypro and cut my "rafts" out of that.  Good news is that I just found out my local independent plastics store sells this stuff for about US$12 per 4 foot x 8 foot sheet--that's less than 1/2 the price of a sheet of plywood.  No staining is required, there's no warping, and the material wipes clean very easily.  Also lots easier to drill with a hole saw, and the material is easily cut with a utility knife.  Lots lighter than plywood too, so it's a cinch to handle.

Any thoughts on all this, anyone?

[Joni Solis]

Thank you Vlad. Good to hear this. Can you tell me where I can find more info about using a biofilter to treat this water before using it in a tray.

Vlad Jovanovic said:

Hi Joni...no I'm not saying it wouldn't work, there would be a way(s) to do it...like by using the 'fish water' that has already gone through a biofilter, and using it in a 'stand alone' Kratky set up...but because of the biological oxygen demand (BOD) that the fish (and perhaps bacteria) place on a system, circulating your water would be important. 

As long as the plant essential elements are in solution, it would work...hydroponic salts need no bacterial action for the salts to dissociate into there plant bio-available form. You could still use fish water or humonia water...it would just need to pass through a biofilter first (so that the nutrients would be present in solution).