Making a heated propogating bench

Hello all. I have got a steel bench which I would like to turn into a heated bench for propogating. I've bought a warming cable and thermostat and am planning to use polystyrene for insulation and sand to go around the cable to form a heat sink.
I'd be very grateful if anyone has made anything similar and/or advise on depth of sand below and above the cable and what other layers to use. The bench top is 'upside down' so has a roughly 1" border which I was planning to make taller by using plastic or wood strips or perhaps polystyrene.
Looking forward to any advice, thanks

 

Hi Philomel, Here's a link to my favourite supplier.....and they deliver to France!
http://www.twowests.co.uk/category/propagator
For the bench, I did something similar last year. Sheet plastic, 2.5cm polystyrene, more plastic sheet, 1cm sand with the cable pegged down using unbent plastic-coated paper clips, 1cm of sand on top and then a 2.5cm layer of perlite.
I splashed out on a high-top cover from Two Wests so I can do cuttings in it as well. It came flat-packed, very easy to assemble. I cheap-skated on the thermostat, though. There's just an old thermometer stuck into the perlite

 

Mine has got 2" of sand under the cables and another 2" on top. A good tip is to lay a sheet of polythene over the top of the sand, this prevents it from drying out because it condensates on the under side of the polythene and drips back onto the sand. It is very important that the sand remains damp so that you get an even heat.The temperature it will be capable of attaining will of course depend on how much cable you use. If you can lay the loops of cable to be only 2" apart that will be much more capable than if they were 4" apart.
This link pretty much explains it all
http://www.twowests.co.uk/category/propagator/soil-heat-cable

 

Thanks very much to both of you for your replies, Noisette and Billybell. I've used Twowests in the past but actually used Baumaux in France this time as I needed some other stuff that they didn't have.
Thats really useful info on how you've both constructed. I found somewhere else on the net that suggested a very similar setup to yours Billybell, so I'll go with that as I already have quite a lot of sand too. I'm going to do my scrimping on the cover Noisette, rather than the thermostat. I'm going to try rigging up my own..... lol. But I agree it's a very good idea to keep the conditions even cosier.
What sort of things have you both used it for? I'm thinking to start with veggie seeds and then perennials, but I'd like to use it for cuttings too. Can't wait

 

This is my set up.I lined with heavy duty polythene then roughly 3" of sand on the bottom ,cable then 3" sand on top.It is important to keep the sand damp otherwise it forms a crust I would stress to make sure it's strong enough to take the weight
This time of the year mine is used for keeping things frost free but I'll soon be cranking it up for seedlings...I plant some cuttings direct into the sand,Lavender,Fushias,Pinks love it

 

Wow, thanks Lolimac, that looks a fab setup! It's giving me even more the urge to get on with mine. Unfortunately only 1C in my greenhouse and below freezing outside, so I'm on in the house jobs today
Its forecast to be warmer soon though, so I'll gather all the things I need and get on with it then
Thanks again for the inspiring photo - watch this space lol

 

Here is mine in use today, not the same scale as Lolimacs excellent set up but the same principle. Because my greenhouse is kept just above frost free I don't usually cover the whole of the hot bed. Anything requiring a higher temperature I cover with propagator lids as seen in the photos. With the thermostat set to 20 centigrade things like tomatoes germinate in about 5 days

 

That looks great Billybell, thanks for showing me. Also made me think, I was going to use expanded polystyrene for the sides but have just realised I'll have a problem fixing the thermostat. Love your idea of reflective walls to maximise the light

Am pleased to report that I have actually done a little to it today. It's snowed indoors as well as out 'cos I've been hot knifing the polystyrene insulation pieces
Have also got the heavy duty plastic liner sorted and rejigged the greenhouse door catch to keep out the draughts. I've been wondering whether to put in a heater to keep the whole thing frost free. It's advised by the warming cable manufacturer as otherwise it may be struggling to keep an even temperature... Do you use electricity or something else? Seems to me it's best to use something on a thermostat, again to keep a more even temperature.

 

You could maybe just make a polythene lid to go over the bench to keep the temperature up and depending on the size of your GH you could maybe just section part of it off to save trying to heat the whole area

@Billybell ...brilliant idea with the reflective 'walls' might have to pinch that one

 

My first things are going to be vegetable seeds and I've read that fleece over them is fine on this kind of set up, so I'll start like that. But I love your cloche style covers Lolimac, so I'm going to look out for something similar. Failing that just hoops with polythene over. my greenhouse isnt huge 2x3.5m, so I'm going to try and insulate it as well as I can and then next winter keep the whole thing frost free as I'm planning to overwinter citrus etc. it's a metal framework lean to that was here when I bought the house. I've used that sandwiched plastic sheeting to cover it, apart from the roof which is c
Thanks for your reply

 

I bought the reflective stuff from Wicks. Its meant for going behind radiators to reflect all the heat outwards. I have it on the North and East walls because I don't get any natural light from that direction. Its also a better insulator than the Bubble wrap which I have on the rest of the greenhouse. This is important to me as I keep the greenhouse slightly heated all winter.

 

Thanks ever so much everyone for your input. This is where I'd got to this morning. I've now got the layers and the cable in and fitted the thermostat. Switched on and it's now already up to the temperature I set. It's dark now so I'll take a photo tomorrow. It only remains to stick some more polystyrene to the outsides. Seed sowing tomorrow?

 

Thanks Billybell, that's great info. Think I was writing while you were posting. As you can see my wall is crying out for the reflective treatment (east wall)

 

Here is my finished bench. Not too pretty with all the polystyrene but hopefully effective. Just need to sort out the top cover now...

 

Well, the bench is now completely full! I've used all sorts of seeds I had hanging around, some ancient, so we'll see what happens.
I've just come across two heated trays that belonged to my husband, intended for wine making. Hmm they'll come in handy