We started with a piece of OSB plywood, and screwed some 1"x2"s (ripped 1x4s) for edges and placed plastic on the bottom to hold the sand. We got some playsand disperse the heat more evenly. It took 3 25kg bags of sand for the whole project.
We poured 1 bag for a bottom layer. We just used a dust pan to spread the sand, maybe a trowel or something might work better, but anything can be used.
Thermostatically controlled heat cable, adjustable at 40-100*F for varying germination temps.
Once the heat cable was spread out in an even pattern to disperse the heat throughout the entire table, we covered it with a layer of sand. We watered the sand to increase the heat dispersion and to increase moisture inside the system, like water vapour in a greenhouse.
The table fits 16 10"x20" seed trays. We're starting onions, leeks, and rosemary with the first batch of starts. Next up will be parsley, rhubarb, and celery.
That's our propagation table, once the greenhouse is up, we'll be making 3 more so we can accommodate all our seed starting flats, we;ll need lots more room once the snow FINALLY melts!
Here's a link to find the thermostat and heat cable:
It was the cheapest place I could find the heat cable and thermostat, its in the states, but shipping and customs fees were reasonable.
I'm listening to rap right now and its got me amped up and wanted to sign-off with some cool phrase, but sadly I'm a white male farmer...I'll try next time, night all!