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I am not sure where to put this so I will ask here as it involves glass etc.

I want to build my own cold frame, can anyone tell me if I would be ok using those thermalite blocks or should I go for the 7 newton high density concrete ones B&Q sell but never seem to have ?

Jeez thermalite blocks? Are you making it bomb and radiation proof?

Mine is built out of old tongued and grooved and recovered twin wall polycarbonate sheet off next doors conservatory.

Well I want it cozy for the plants you know :o apart from just putting things in to harden off I want to put melons in it, and if I put it up against my back wall I can also shove a heater in it. Then of course, theres the cost of these blocks, at about a £1 each it isnt a lot is it. Not for 2.7m x 1m three courses high.

I  constructed  a cold  frame this year from timber which accommodates thirty seed trays cost me less than fifty quid including the sheets of plastic, already paying dividends in the returns I have had from the seeds I have put in,  :)

Quote from: Mr Smith on May 07, 2010, 20:56:06
I  constructed  a cold  frame this year from timber which accommodates thirty seed trays cost me less than fifty quid including the sheets of plastic, already paying dividends in the returns I have had from the seeds I have put in,  :)

I built a Pollytunnel for £50

"twin wall polycarbonate sheet off next doors conservatory. "

I have 4 sheets of this, and have set them up over some seedlings as a sort of ridged tent with ends blocked by glass.

I am coming to the conclusion that they don't let enough light through, or are possibly even reflective, to stop the conservatory getting too hot. The seedlings look pale and drawn (perfectly good soil, enough water).

Does anyone know if this is true?

if the plants are getting leggy then i would say its not letting enough light through

Polycarbonate has better transparency than glass.

unwashed. I got enough timber from Barlows at hermitage cheap to build one but I like the idea of permanent and non rot. Only cost me £30 too. So I see a couple of raised beds coming or a heated propogating tray or two.