You will need a sharp cutter and a metal ruler to cut out the rectangular panel on the bottom and top of the box.
I was on a roll and finished cutting this many boxes. You can see where to cut the styro box to get the biggest possible panel.
Kuya Ric asked for the castoffs when he saw it. He said he was going to melt them and use to patch up their tin roofing.
You will need to wash the styro panels thoroughly with water and detergent. I used a soft scrub brush to clean the surfaces of dirt and any fungicide that might have gotten to it when the grapes were sprayed with the chemical to make it last longer. (I saw a sticker warning on the box about the fungicide spraying.) Dry the panels thoroughly. Place them on a table under the sun.
You will need to glue two pieces of panels together. One panel would easily give way to the forces exerted by the shrinking paper but two would be sturdy enough to withstand the pull forces. You can use Elmer's glue or if you can find styro glue like the one shown on the right, that is even better.
Weigh the panels down with books on top to get a better bond between the panels. Set aside and come back to it the next day.
With sandpaper I wrapped around a box of soap, I smoothed the surfaces and sides of the stretcher. Even did a bit of beveling and rounding of sharp corners. Wear a face mask when you do the sanding. You would not want to get styro dust into your respiratory system.
I coated the surface with gesso. You can skip this part. Not really necessary except that I had some leftover gesso lying around. Much later though, I noticed the gesso somehow helped protect the panel by making it easier to lift the gummed paper tape off the surface with little or no damage left behind. Run water over the surface and get rid of any gunk left behind. I dried the board under the sun. Looks good as new and ready for stretching again.
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