What Material Do I Use to Make My Raft
For a good introduction to Rafts reference see Rafts Troughs Liner and Rocks
For information on constructing rafts see Raft Building and Liner Installation
Photo credit www.drenergysaver.com
XPS – Extruded Polystyrene
The best material to use to make rafts for you Aquaponics system is Extruded Polystyrene (XPS). Extruded polystyrene (XPS) comes in pink or blue, is closed cell, square edge, has a smooth plastic surface, and panels typically aren’t faced with other material, like foil or brown paper like some other foams are.
The R-value is about R5 per inch of thickness. This type of rigid foam won’t absorb water like polyiso and is stronger and more durable than expanded polystyrene (EPS). XPS won’t water log and is resistant to damage from destructive marine growth.
The Dow STYROFOAM blueboard comes scored or not scored.
STYROFOAM Square Edge is an extruded polystyrene foam insulation board with square edges on four sides. Offers superior water resistance, long-term thermal performance and high compressive strength.
“Scoreboard” is scored longitudinally on 16″ and 24″ centers, making it easy to snap into convenient widths for construction.
You want to use the versions that are not scored (for easily breaking), and have no chemical additives like mold preventative, etc. The easier to use and better insulator for the water in your raft way is the 2″ thick version of the XPS foam.
Here is and example of the cost for STYROFOAM 2″ Square Edge – 4′ x 8′ $37.76
EPS – Expanded Polystyrene
Expanded polystyrene (EPS) is the least-expensive type of rigid foam and has the lowest R-value (around R-3.8 per in.). It’s also more easily damaged than the other types of rigid foam. A brand name for EPS is Styrofoam .
Polyiso – Polyurethane (PUR) or Polyisocyanurate (PIR or ISO)
Also referred to as PIR, polyiso, or ISO, Polyisocyanurate foam has the highest R-value per inch (R-6.5 to R-6.8) and often comes with a reflective foil facing on both sides, so it can also serve as a radiant barrier in some applications. Polyiso board is more expensive than other types of rigid foam.
It is made with Methylene diphenyl diisocyanate which is an allergen and sensitize. Polyiso is believed to be toxic, even after the manufacturing process, with reports of fish mortality when used as rafts in Aquaponic systems.
Fully reacted polyurethane, itself, is chemically inert. The problem is that the stuff you can buy at the hardware store is typically “improved” to increase the insulation properties (R value). This “improvement” is achieved by adding isocyanurates, which are hazardous chemicals. The list of potential human hazards from exposure to isocyanurates is long and scary – and I wouldn’t want my fish exposed to this stuff (or have the roots of my plants bathing in a weak isocyanurate solution). Folks on the web will often equate pink foam with polyisocyanurate, but that is not necessarily the case. Check the chemical composition of the foam you intend to buy and just make sure you’re getting XPS and not PIR or ISO (Credit for Paragraph)
Watch for “additives” to the foam sheets. It is rumored that some manufactures add chemicals to discourage bugs or flame retardants to the foam sheet or to its paper or foil covering. Avoid these products.