I love Aquaponics but have yet to start my own set up. I'm still trying to fill in my knowledge gaps.
I am concerned about Styrene leaching into food from Polystyrene floats used in DWC, Anyone know anything that will stop me being concerned? Everyone seems to think it's only a matter of time before Aquaponically grown food is classed as organic but this will not be the case for DWC using Polystyrene floats.
Hope someone Knows more than me (should be easy!)
Jon, if that's the way those paints work, than it certainly would seem like you'd be better off with an interior latex paint. Friendly's (according to them) uses Bright White Exterior Latex Semi-Gloss enamel for painting rafts...I'm not too big on my rafts being colorfast, but would like as little of that paint to slough off and end up somewhere else...Thanks for that info. As always your $0.02 is well worth it.
While we're at it...Do you see any difference in the way the paint would be applied to a raft? i.e paint gun vs. paint roller? Not so much in terms of ease, but adhesion?
I don't know about in the states but here the yellow and pink polystyrene from Austro-Therm are the same as DOW blue board (no fire retarding additives) except that they are slightly less dense (the difference is 2kg/m3). There is other foam board that is grey or green that contains additives to keep the smoke down in case of fire and some other stuff...flame retardant I think...maybe those boards with such additives is what TC was referring to?
You could always try a side by side with some flat rafts vs. the ones with the dome and off-set? Seems to make sense though.
Bamboo sounds great (I wonder how they hold up over time?) now if you could just get them to exude iron sulfate slowly over time hehe...
Friendlys is where I heard NOT to use the Pink because of some chemical in it. I don't really know, I've not done rafts.
As far as the dome effect in the rafts, I could see the benefit of allowing a bit of an air pocket around roots. And then there is the drawback that the root mass will likely grow out of the net pot in all directions more instead of just straight down and if the raft is thinner right around the plant hole, Pulling the net pots out at harvesting would likely cause more damage to the foam around the holes on the rafts. Again, this is just guess work on my part since I've not really done it either way.
As to gravel size, I don't pre-filter solids but I've done just fine with the 1/2" river rock. I think to me the "perfect" size would be the stuff that goes through a 3/4" screen but doesn't go through the 1/2" screen so that would probably be called 5/8" if you had to pick just one number but I've never seen gravel listed that size or range.
Maybe Friendly's or someone can expound upon the difference between the Owen Corning (pink) and the Dow Chemical (blue) polystyrene boards. Or what specific chemical people in the US should potentially be worried about?
I'm gonna take a guess and say it's hexabromocyclododecane (which is a flame retardant that Owens Corning is known to use in some of it's products). This hexabromocyclododecane is up for global banning by the Stockholm convention because of its toxicity and ecotoxicity. (Even the American EPA put it on some kind of concerned list in 2010...)...
The Dow blue board is extruded polystyrene styrofoam. The Friendlies warn against using polyisocyanate foam, commonly pink or white in color.
Edit timed out...
Their stated concern is that the chemical is related to cyanide. They tell of someone experiencing 10% fish loss after putting pink rafts into his month old system......
Aha. OK because Owen Corning makes an extruded polystyrene foam board as well, only it's pink in color.
Just out of curiosity...what's the deal with polyisocyanurate boards? (And not to split hairs, but these things can be important sometimes...like the difference between chloride and chlorine...but I think all commercial polyiso rigid foam boards are polyisocyanurate, not polyisoisocyanate).
Well, hold on a minute...there would appear to be a pretty big difference between cyanates, isocyanates and isocyanides. Three totally different functional groups with totally different behaviors...There should not be anything even remotely related to cyanide in a polyisocyanurate foam board...
@Jon. What you say about the sloughing of exterior latex paint makes sense, but I guess the other side of that coin would be that interior latex paints are not formulated (resins) with any significant temperature fluctuations in mind (like in my greenhouse), so it seems that they would be more apt to be brittle and crack/flake/peel off...Maybe a interior/exterior combo paint would be the best choice? IDK. IDK if every manufacturer's int/ext paint is created equally either?
On a side note even though I can't for the life of me find a connection to polyisocyanurate and cyanide...This may be an example of a "good kind" of confusion, as (get this...) according to the Owen Corning people, they confirm that they do in fact use hexabromocyclododecane in there pink extruded polystyrene boards for fire protection 0.5% - 1.5% by weight.
This is a chemical up for global banning due to toxicity and ecotoxicity issues, but it's cheaper for them to use than the alternative) The pink color is to distinguish from their competitors extruded polystyrene board (blue board from Dow Chemicals).
Dow Chemical does not use hexabromocyclododecane in their blue board:
Styrene, polymers 9003-53-6 >= 60.0 %
Styrene butadiene rubber 9003-55-8 < 40.0 %
1,1-Difluoroethane 75-37-6 < 5.0 %
Talc 14807-96-6 <= 1.0 %
Owen Corning extruded polystyrene:
Polystyrene CAS#9003-53-6 80 - 90% by weight
Talc CAS#14807-96-6 0 - 2% by weight
1-Chloro-1, 1-difluoroethane (HCFC-142B) CAS#75-68-3 7 - 12% by weight
Hexabromocyclododecane CAS#3194-55-6 0.5 - 1.5% by weight
I'm don't know weather or not this will leach into an AP system, but it would seem silly to use/buy/support it. So, Friendly's without even knowing it, did us all a big favor by warning us against the use of "pink board". I understand that Friendly AP were warning against an entirely different product, for different reasons, but still...Very cool the way it turns out.
Jon if you or anybody else have any more thoughts/ideas on the paint matter I would appreciate hearing them. My dilemma is this:
The one single importer of latex paint here only imports either exterior or interior so I have to choose.
I'm not thrilled about the sloughing properties of exterior paint, but I'm not thrilled about the rigidity/brittleness of the interior latex paint either, and think it might actually be worse in a greenhouse application due to the extreme fluctuations in temperatures that the painted surfaces would be subject to...
Any pointers would be appreciated. Does anyone know if the combo int/ext latex paint is a third unique formulation of resins, or do the manufactures just blend the two (interior paint with exterior paint) to create the combo product? (As is the case with motor oils i.e synthetic oil/mineral oil blends).