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?

[Eric Warwick]

That is the best salviging techinique I've ever heard. Other than the exceptions of a  few local candidates and causes I volunteered for this year, the endless campaign signs all deserve no more than to be covered in slime--such as the politicians. (Is it strange to be cynical at 15?) Anyway, without a diagram I'm sure to misinterpret your question, but I'll try. What you described is more of an old form of NFT (nutrient film technique), and there are certian advantages to it. One is that it requires less material and water. Since your sheets appear to be food grade, there is no risk of contaminants leaking to the surrounding water. The only problem I see in this design is what happens, and this will  happen, when you decide to expand your system to include more plants. Though there is no challenge, in theory, to scale up your system, the materials will either get increasingly more expensive, or require more and more labor. This amounts to what you see your time and, depending on your age, your back is worth to the amount of money you can spend. Not a huge problem. In any case, I now know what to do with all those Rodney Tom* signs. 

*Washington State Sentate Majority Leader, don't bother asking. 

Sorry for, probably, failing to answer your question. 

[Paul Trudeau]

Hey Eric,

Thanks for the reply.  No, this isn't NFT.  Here's a picture to give a better idea:

(blue/white "raft" on far right is polypro; other 3 - 4 white ones are plywood; note clips on near edge of middle tray to inhibit warping)

The water depth under the plants is about 7 inches.  Not as deep as say UVI-style raft system, but functionally lots closer to that (ie enough water mass to avoid quick water temperature fluctuations) than to NFT, where water depth is a fraction of an inch.

My system has 3 trays of lava rock for biofilter and solids capture and 11 "raft" trays.  Yes, if I were going much larger I'd do a different design, but this suits my current needs just right.

Paul

PS:  always great to hear from a young person.  Keep up the good work.

[Vlad Jovanovic]

Eric, what Paul is describing sounds more like an updated Gericke method, as described by Kratky,B.A., 1996, Non-Circulating Hydroponic Methods, DPL Hawaii, Hilo, HI.

I've liked it before in other discussions, but here it is again... http://www.ctahr.hawaii.edu/hawaii/downloads/Three_Non-circulating_...

From a nutrient standpoint the PDF doesn't deal with AP or anything, but it's got some pretty cool hydroponic sub-system ideas in it nonetheless. And passive at that... I remember you had brought up the "passive hydro" topic to TC about a year ago, so you might dig the link Eric...

At any rate...It's nice to see those campaign signs actually fulfilling a useful purpose. Way to go Paul  No staining, no warping, no glues/binders...nice.

You may want to protect them from the suns UV rays somehow (IDK, a sheet of something or another...tin foil...whatever), they'll probably last longer that way.

[Paul Trudeau]

Thanks for the info Vlad.  Good idea to be aware of the UV issue.  Hope this stuff lasts a long time, but pretty cheap to replace when necessary.

Glenn's design (and mine) does circulate, not passive like your example.  Flow in mine is FT --> biofilter --> raft trays (in series) --> sump --> FT

[Alan McKnight]

I read somewhere that the plastic sheeting they use on bill boards is a great source of plastic and that the sign folks give it away. Just happens I have my step sons 30th birthday  tonight and one of his friends works on the bill board signs and will be at the party. So I will see what I can find out and let the group know.

Sorry I have been off line for a while but I caught that plague  flu and it knocked me for a loop this month.

[Chris Carr]

Great idea reusing those signs Paul. Keep in mind that the ink never really comes in much/any contact with the water so it might not be that big of an issue. The campaign office can probably also refer you to the print shop that made them if you wanted more info about the ink. If it seemed to come off easy then a pressure washer might make quick work of it too!

With so many local elections this is a great source for just about anyone. The campaign offices would be glad to give them away (assuming they aren't saving them for next election and you can convince them you arnt going to make some type of political hate art project out of them).

[Paul Trudeau]

Thanks Chris.  I did inquire with one printer who said they'd get back to me about the content of the ink but they never did.  May be OK to use the signs with printing on them, but for $12/sheet, I'm going to go ahead and put all inkless stock in my system.  Also need a bigger piece for a tank cover, so I need to get a sheet anyway.  There are probably lots of other possible reuse applications for the signs - I'm hanging on to my extras!    

PS gotta give props to my buddy Randy, who originally suggested the sign material for an aquarium top for our aquaponics display at the state fair last summer.  

[Eric Warwick]

Rather than thread-jacking this, I'm going to create a new one in the Fish-less Group.

Vlad Jovanovic said:

I've liked it before in other discussions, but here it is again... http://www.ctahr.hawaii.edu/hawaii/downloads/Three_Non-circulating_...

From a nutrient standpoint the PDF doesn't deal with AP or anything, but it's got some pretty cool hydroponic sub-system ideas in it nonetheless. And passive at that... I remember you had brought up the "passive hydro" topic to TC about a year ago, so you might dig the link Eric...

[Vlad Jovanovic]

Yes, it would be tough to come up with a non-circulating AP design (I threw in the passive examples for Eric's sake, I figured he'd appreciate it). But really this method has worked for me both circulating, and non-recirculating, with extra air, and with no extra air...It works great.

@Alan, the sheeting used on billboards is "not really plastic", it's vinyl (pliable PVC). And being a pliable PVC, it isn't really appropriate for use in a re-circulating food production system IMO, because of the phthalates used (which leach...and have been linked to things like endocrine disruption, breast cancer, and a host of other not so fun stuff)...

http://community.theaquaponicsource.com/forum/topics/what-is-wrong-...

Paul Trudeau said:

Thanks for the info Vlad.  Good idea to be aware of the UV issue.  Hope this stuff lasts a long time, but pretty cheap to replace when necessary.

Glenn's design (and mine) does circulate, not passive like your example.  Flow in mine is FT --> biofilter --> raft trays (in series) --> sump --> FT

[Alan McKnight]

Well the sign stuff turned out to be a bust. I guess on the bill boards I was thinking  about, they use a special metal, and the sign is then put on in strips like wall paper.  So back to the drawing board.

[Paul Trudeau]

Just picked up my unprinted sheets of new corrugated polypro.  Vendor had 2 tips:  try sealing off the edges with a bead of silicone so that water doesn't get in there and grow mold.  Few if any adhesives stick well to this type of plastic, but silicone might stick well enough for this application.  I think it's a good idea.  Second, she said when printers make a mistake, they remove the ink with denatured alcohol. So perhaps the ink on recycled campaign signs could be removed for our purposes.  I'm not enthusiastic about using a bunch of denatured alcohol though.  

[Vlad Jovanovic]

Paul, you might want to try some sort of polyurethane combo adhesive/sealant like 3M's E5200 or E4200. They now make a version (E5200) that cures in 24 hours instead of the standard stuff (like I have) that takes 7 days to fully cure. It has been my experience that regular old silicone "doesn't stick for shit". Though I'm sure that there may be some specialty types that adhere better.

The E5200 marine sealant/adhesive has worked real well for me so far... on a variety of materials, including ones that usually don't bond well (HDPE, LDPE etc) and normally have to be thermally bonded.