Making a cheap concertina blind using greenhouse shading

Vertical blind, half open

Roof blinds - 1 closed, 1 open

For Christmas, I wanted to give my wife a set of greenhouse shading blinds for her new greenhouse.

However, when I priced them up, the cost was going to be over £500. I decided to make some instead.

Turns out they are not difficult to do, and, as I could find no instructions on the Web, I decided to write up how to do it here on this blog.

The blinds shown here can be used vertically (as in the picture above), or horizontally (on the roof). In either case the moving rail (white in the picture) always stays parallel to the top and bottom rails, due to the guide lines threaded through it.

The blinds can easily be opened and closed by pulling or pushing either end of the moving rail, and will stay in any position.

Materials

• Greenhouse shade netting
• Strimmer line
• Plastic electrical conduit, oval section
• Wood strips (about 1" x 1" - 25cm x 25cm)
• Rust proof screws (brass or stainless steel)

Method

First measure the area to be covered. I suggest making the blinds no wider than about 4 ft (120 cm), as the electrical conduit which forms the handle to open and close the blind bends if you use longer lengths.

Cut the shade netting to the width to be covered, and about one and a quarter times the length.

Pleating the blind

Using a ruler to guide the pleating

Using an iron on the appropriate setting for your material (nylon for shade netting - not too hot, or it will melt), fold over about an inch of one end of the blind, and iron the fold in.

I used a long metal ruler about an inch wide to help me get the folds straight and the correct width.

Fold and iron again, and repeat until you have pleated the full length of the blind.

I found the weight of the material hanging off the ironing board tended to pull the pleats out, so I used some weights (a couple of square bottles of water in the picture) to stop this happening.

Obviously you will have to unfold earlier pleats as you go, otherwise the material gets too thick and difficult to handle.

The pleats do not have to be totally accurate, but it is important to make sure they are reasonable square to the edges of the material (and that the material is cut squarely).

When you have finished, gather the pleats up carefully (I found starting from the middle was easiest), and tie with some pieces of string to hold them in place. Make sure the edges are all squared up.

Make the mechanism

Pleated blind with top rail threaded

Cut 2 pieces of the wood the same width as the blind, and 1 piece of the electrical conduit.

Drill holes for the strimmer cord - one close to each end, and one in the middle. The holes in the 2 pieces of wood and the conduit should all line up. Also drill diagonal holes in the ends of each piece of wood as shown.

Thread the blind

Threading diagram

The 3 main strimmer lines should be a little longer than the drop of the blind (enough to allow plenty for knots, and a bit extra for adjustment). The 2 guide lines (the ones that go through the conduit) should be longer by the length of the conduit - best to allow a bit more for adjustment, as these lines should not be as tight as the main lines.

First thread the two guide lines though the length of the conduit. Then thread the 3 main strimmer lines through the top wooden rail, the blind, the conduit and the bottom rail as shown. Tie figure eight knots in the ends.

Thread the ends of the guide lines though the diagonal holes - notice that one line goes from top left, through the conduit, and down to bottom right, and the other vice versa. Again, tie them off with figure eight knots.
Now fasten the blind to the top rail (I used a staple gun), and to the conduit (I used gaffer/duck/duct tape).

Detail showing guide line (blue) threaded in top rail and conduit

Fit

Drill holes in the top and bottom rails for the fitting screws - the placing depends on what you are screwing them to. Fasten the top rail in place, and hold the bottom rail where it is to go. Adjust the length of the main lines so they will be quite tight (a little stretched) when the bottom rail is in place. Temporarily fasten the bottom rail, ready to adjust the guide lines. For horizontal blinds the guide lines can be quite loose, but for vertical blinds, they must be tight enough so the blind does not close under its own weight. Once you have measured and tested, undo the bottom rail and tie the knots to make the lines the right length. Professionally made blinds do not use knots, they have a small piece of metal tube with a grub screw, so you can pull the right length of line through the tube, and tighten the screw.