convert a soil warming cable into a heating mat

[Jenny]

Hi I have a soil warming cable and thermostat that I used to have in a sand box on a bench in my greenhouse. However it was very heavy and my bench collapsed. So I thought I would update my bench and propagator and use the soil warming cable to make a pad similar to this.

what type of material should I use to make the pad from? And how would I fix the cable to the material? I suppose I could put it in the middle of two layers and sew it in place with nylon fishing line but would that melt with the heat?

I did try using a sheet of expanded polystyrene but the cable is melting into it plus I used cable clips and they keep coming out of the polystyrene and I am worried it might catch fire.

So any suggestions? Thanks, Jenny

[Stuart Noble]

Wouldn't an electric blanket be easier? A bit bigger than your bench maybe

[Jenny]

But I have the soil warming cable and the thermostat also I need the electric blanket to heat my bed at night

Jen

[Stuart Noble]

I imagine the pad is just the cable sandwiched between plastic sheeting, but who knows what grade you would need to withstand the heat? Maybe you should contact

surface, so it's not surprising it gets hot.

[Rob G]

No the pads are a carbon mixture sandwiched between to layers of plastic.

Rob

[Andy Dingley]

I don't think you can. The lightweight pads have a distributed heating element, you have a cable. Your conversion is going to need something that spreads the heat from the cable sideways a few inches, and holds the cable in an evenly spaced zig-zag.

Simplest option sounds like reinforcing the bench and a thin-layer sand box, with the cable in it. Maybe use a lighter compost than sand, or damp wood ash.

Alternatively, a sheet of thin metal with insulation beneath it. Polystyrene might do, if the heat is more distributed than bare cable. Otherwise a layer of wood ash, which is light and a good insulator (so long as it's dry).