How to Build an EcoPropagator

Latest Update 3rd July 2017.

The EcoPropagator (the one in the middle of the photo above with netting in place) uses its external 9mm marine ply walls to contain the water tank instead of using a bin.  The bracing is on the outside of the propagator so it doesn't interfere with the water tank's liner inside.

Set this 42 x 19mm plantation pine timber bracing about 10mm from the top and the bottom of the front and back walls.  I use five 25mm gal button head wood screws to fix each brace in position and 75mm gal c\sunk wood screws to secure the side walls to the ends of the bracing (1 in each end).

The same plantation pine timbers are used to make the frame for the propagator's cover, and 75mm gal c/sunk wood screws are used to join the horizontal and vertical members (2 per joint).  This frame is covered with 0.9mm polycarbonate sheet in winter and 21% shade polyethylene netting in summer (VegNet).  Timber blocks are fitted to the underside top of each vertical leg so the frame doesn't slide off the propagator.  The assembled propagator is painted with 2 coats of external water based acrylic paint to shield the soil from the marine ply's chemical treatment and to protect the untreated plantation pine.
The whole area inside the cold frame can be used for propagating by using 2 layers of 200 ┬Ám plastic sheet as a liner for the water tank.

The plastic liners (which rest on the ground) are suspended in position by stapling them along their top edges to the walls of the propagator.  The design of the filling, distribution and overflow unit is similar to that used in full sized Ecobeds.  The water tank depth is 160mm.
This picture shows the tank being filled with rainwater and Scoria.  When the water starts to overflow through the overflow tee section turn the supply off.  More Scoria is added until it is level with the water.

A piece of horticultural fabric or heavy duty shadecloth is placed over the Scoria and cut 25mm oversize on each edge so it can be turned up the sides of the unit to seal the tank when the soil/compost is added.
About 50mm of sieved soil is added to the bed and covered with 50mm of high quality sieved homemade compost..  This soil/compost wicking medium stays moist at all times as water is wicked up from the water tank.  Up to 90 mini pots and small jiffy (fibre) pots containing seedlings growing in organic potting mix are buried up to their rims so that moisture and beneficial microbes can migrate from the biologically active soil into the seedling's root zone.  Here the microbes quickly establish symbiotic relationships with the seedlings.

A timber frame is covered with VegNet for the warmer months.  It keeps insect pests out of the propagator and shades delicate seedlings from hot sun.  In the cooler months, the VegNet is replaced by 0.9mm thick polycarbonate sheet to trap sunlight and maintain a moist warm environment inside the unit.  To maximise the heat gain, black plastic sheet is pinned to the back wall during those months.
Vents are installed in the top corners of the propagator to remove air if it gets too hot on sunny days in the cooler months.  A VegNet filter is stapled over the opening inside the propagator.  It keeps insects out when the vent is open.