Category: Making

Projects that make or build something.

Post #1899: Composting shed, testing

My tumbling composter doesn’t work in the winter. Which is ironic, given that it was made in Canada.  But it’s a common problem.  Winter composting is a problem for anyone who tries to compost small amounts of material outdoors, in a cold climate.  Composting stops as the temperatures drop.

So I made a little insulated shed, to fit around the composter. 

The upshot is that, so far, it seems to keep the compost around 16F warmer than it would otherwise be, without the shed.  On average.

I’m not sure that’s going to do the job. Continue reading Post #1899: Composting shed, testing

Post #1897: Re-using political yard signs. Composting shed, Part 2

 

In honor of election day, I’m re-using a bunch of political yard signs to build a small outdoor shed.  The Coroplast used for high-end campaign signs is far too good to be tossed out just because somebody lost an election.

I’ve decided on the following method of construction:

  • Coroplast campaign yard signs
  • Stapled to furring strips

It’s every bit as complex as it sounds. Continue reading Post #1897: Re-using political yard signs. Composting shed, Part 2

Post #1896: On re-using political yard signs: Composting shed, part 1.

 

Today is the day when a whole lot of campaign signs go straight into the dumpster.  Along with the political aspirations of half the recent candidates,

Which is a pity, really.  (The signs, I mean.)  The best of those signs are made to last a long time.  We really ought to do better than treating them as a single-use disposable.

So I suggest that the first Wednesday following the first Monday in November be declared Campaign Sign Recycling Day.  In keeping with that, today is a good day for me to make something useful out of some dead political yard signs.

This post is the theory.  Next post is the actual assembly.

We’re talking Coroplast.

Source:  Coroplast, Inc.

Campaign yard signs come in several varieties.

Cheap campaign yard signs aren’t re-usable in any obvious way.  Some are coated cardboard, on some sort of stick.  Some are a printed plastic sleeve that fits over a three-sided wire frame.  For both of those, the metal frames (if any) can be recycled.  But the signs themselves aren’t good for much.  Far as I can tell, once they’ve served their purpose, they’re trash.

By contrast, high-end campaign yard signs are Coroplast(r).  That is, corrugated plastic sheets — two sheets of plastic bound together with thin plastic channels.  As pictured above.  Effectively, they are built like corrugated cardboard, but plastic.

These sheets — typically made from polypropylene — have a surprising amount of structural integrity.  Much like corrugated cardboard, they are quite resistant to bending or folding across the corrugations.  This means you could  use a single thickness of Coroplast to build light-duty objects, and multiple thicknesses to build heavy duty objects.

These also stand up well to being used outside.  The ones forming the sides of my oldest raised beds now have more than five years of cumulative outdoor exposure (first as yard signs, then as raised bed sides.)  Only this year did they begin to show brittleness from all that sunshine and weather.  (And if I’d cared to keep them painted, I probably could have avoided that, as most of the damage is from exposure to the UV in sunlight.)

Fastenating

I’d say that the biggest downside is that these can’t be glued together.  (Or, at least, not well, or not easily, using conventional glues).  The underlying material (typically, polypropylene) just doesn’t stick to much.  And the ink coating — the printed message — further complicates things.

Near as I can tell, most people who make DIY projects with Coroplast sheet opt for some sort of mechanical fastening.  That can be as simple as cutting slots and tabs, so that sheets fit together.  Than can include melting sheets together, in places, to form a sort of plastic rivet.  Or can include using actual metal fasteners (bolts, washers, nuts) to hold the plastic parts together.  Or staple or nail them into a wood backing.

(The big exception being model airplane enthusiasts, for whom gluing coroplast is the only practical option.  That said, after having read one or two sites discussing that use, I’m convinced that gluing up Coroplast is not something that you’re likely to get right the first time.)

There are chemical methods that might, in theory, hold these sheets together.  Some are specialized glues specifically designed for this sort of application.  All of those appear to cost an arm and a leg, at least for the quantities that would be needed to build (e.g.) a piece of furniture.  And then there’s solvent-welding the polypropylene (PP).  That is, finding a solvent that will dissolve PP, dissolving some pieces of PP in that solvent, and then using that as if it were glue.  I strongly suspect that either approach — specialized glue, or DIY solvent-welding — requires a nice clean PP surface, involving a lot of complicated surface preparation, and that the ink firmly bonded to the typical campaign sign would interfere with that.

Dare I say this?  Even duct tape is iffy.  The same factors that make it hard for glue to stick, make it hard for tapes to stick.  And surface preparation for taping is not easy (e.g., lightly torching the PP surface).  All told, taping or gluing this stuff seems like a lot of work, on the off chance that you can get something to stick firmly.

The upshot is that I’m going with mechanical fastening only.

Never in small amounts

I find most plans for upcycling or recycling of materials to be of little value.  Most involve using small amounts of materials.  Most involve creating something for which there is a very limited demand.  The results tend to be more of a novelty than a way to divert significant amounts of material from the landfill.

Contrast that with using campaign signs for the sides of raised garden beds.  That used up a lot of material, slowed down the inevitable progress toward the landfill by years, and avoided consuming considerable amounts of virgin materials.

In this case, I have a stack of roughly 35 campaign yard signs, or about 100 square feet of Coroplast sheet.  Pre-cut into neat 2′ x 1.5′ pieces.  So I’m looking for a project that will use up just about that amount of material, and give me something useful in return.

Revisiting cardboard furniture

Source:  Google search

In Post #887, I did up a quick summary of the various construction methods used to create corrugated cardboard furniture.  I’d guess that just about anything you could build as corrugated cardboard furniture could also be built out of Coroplast.

So if you are stuck for ideas, you can look up cardboard furniture plans.  As long as they don’t depend critically on glue, they ought to work with Coroplast.

As I see it, the main approaches to creating weight-bearing structures for cardboard furniture are:

Simple stacked sheets.

Source:  Homedit.com

Folded beams

Source:  Time, inc.

Structural grids (with or without surfacing materials):

Source:  Planet Paper

Totes

Source:  Storage Techniques for Art, Science, and History

It seems worth mentioning that a lot of lightweight commercial bins and totes are made from folded and fastened sheets of Coroplast.  It’s such a common use that there’s even a market for used Coroplast bins and totes.

You can find lots of different plans on the internet for constructing Coroplast totes, bins, boxes, and so on.  They all boil down to folding a sheet into a box shape, and then somehow fastening it together at the corners.  In the example pictured above, the author constructs a sort of “rivet” out of hot glue, and uses that to fasten the corners mechanically (reference).

Here, I’m shooting for something larger, to use up more Coroplast signs.

From dead campaign signs to structural integrated panels.

Source:  Builder Bill

I’m going to turn my pile of used Coroplast into some structural integrated panels or SIPs.  In this case, the SIPs will be flat, rectangular wooden frames, faced with coroplast sheets, and filled with … probably scraps of insulating foam board.

Like a hollow-core door, if you’ve ever dealt with the insides of one of those.  The entire frame around the rim is solid wood, and so has enough strength to hold fasteners and hinges.  But the broad flat surfaces are just thin, rigid sheets backed by some hollow, honeycomb-like structure.

As long as those rigid face sheets stay firmly in place, the entire unit ends up being quite strong, given the light weight.  Far more than you might reasonably expect.  This is why (e.g.) you can easily use a hollow-core door as a table-top, even though the individual face veneers are far too flimsy for that use.

I think this takes good advantage of the strengths and weaknesses of Coroplast.  And it allows me to connect the Coroplast to the structure using a (hardware) staple gun, which is about as fast and as lazy as it gets.  But all the connections subject to high point loads — the sort of connector that would pull out of a thin plastic sheet — can be made through the solid wood edges.

And it’s generic.  I’m going to use this to build a little knock-down insulated shed for my composter.  But nothing would stop you from (e.g.) building furniture this way.  Bookshelves.  A larger shed.  A lightweight travel trailer.  Anything that can be made from rigid flat panels can be made this way, within the strength limitations of the materials.

 

From structural integrated panels to winter composter cover.

At this point, putting the composter cover together is just a matter of connecting the panels made in just above.

Ideally, I’d like to have “knock down” construction — something that can be easily disassembled and re-assembled without tools.  (That way, I can store it away easily during the off-season).  But in the end, this is only going to take four long screws to hold it together.  So I’m just going to screw it together.

How this actually goes together is going to depend on what scraps of lumber I build it out of.

Conclusion

In this post, I figured out how I’m going to use up a lot of 1.5′ x 2′ Coroplast campaign signs.  My proposed method is to build a bunch of “structural panels” out of those signs.  That is, thin wood frames faced front and back with Coroplast sheets.  And then use those rigid panels to build a structure.

This approach:

  • Uses up a lot of signs.
  • Doesn’t require gluing the Coroplast sheets to anything
  • Uses (hardware) staples as the main fastener
  • Avoids putting high point loads on the plastic sheets themselves, by placing all the “structural” fasteners into wood.
  • Is flexible — just make the panels different sizes.

All I have to do now is to make that happen.

I’m now going to test that, by building a winter cover for my composter, using that “structural panel” method.  Assuming all goes well, the construction of that should be documented in my next post.

Post #1866: Winter composting, take 2, using an indirect solar air heater.

My roll-up solar air heater is putting out about 2200 watts of power, in the form of heated air, in the mid-day October sunshine, 37 degrees north latitude.

But absent some sort of magic, that’s not enough.  Not on its own, anyway.  To keep my composter working through the winter, I’d have to build an insulated box for it, and pipe the hot air into that box.

I’m not even sure that would work.  And even if it did work, I’m not sure it’s worth the effort.

Continue reading Post #1866: Winter composting, take 2, using an indirect solar air heater.

Post #1858: Indirect solar food dryer, Part 2: Building a roll-up solar air heater.

In a nutshell:  In an afternoon, I made a roll-up solar air heater using plastic sheeting, a pile of green mesh vegetable sacks, some tape, and a fan.  At solar 3PM, that’s now putting out a nice stream of air at just under 130F.  That should be adequate to serve as the hot air source for drying food.

See the just-prior post for the theory.  In particular, why a mesh-filled tube is a pretty good choice for a solar collector.

When I’m done with it, I can just roll the whole thing up and store it in a nice, compact package.

Background

I want to make a solar air heater, to use for drying my garden produce.  Mainly, for making dried tomatoes.  Solar-powered, because otherwise, in the humid climate of Virginia, my only reliable option is to use an ungodly amount of electricity to make those dried tomatoes..

Source: Post G22-010.

At this point, I’ve exhausted all of the simplest solar-drying options.

Even in Virginia, if you get perfect drying weather for four days in a row, you can dry tomatoes using old-fashioned open-air drying (Post G23-056).  The problem is, you can rarely count on a stretch of weather like that, around here, when you need it.

I also tried making a simple power-ventilated direct solar food dryer.  (That is, a clear-topped, ventilated box in which sunlight shines directly onto the food to be dried.)  My conclusion is that direct solar dryers just don’t have enough power to dry tomatoes reliably in my humid climate (Post G23-058, Post G23-057).

My aha! moment came when I realized that direct solar food dryers are simple flat-plate solar air heaters.  The food sits on or above that flat plate.  Simple flat-plate solar collectors are the least efficient way to convert sunlight into heat energy.

So here I am.  My late-season tomatoes are (finally!) ripening, so it’s time to get this done.  I’m upping my game by making an indirect solar food dryer.   This is a dedicated solar air heater, hooked up to a box that contains the food to be dried.  That arrangement allows you to increase the power input, both by increasing the efficiency of the solar energy capture, and increasing the ratio of solar energy capture area to area of food to be dried.

Celebrating the cheap and flimsy design.

Source:  Government of New Zealand.

Funny thing about the word “cheap”.  Once upon a time, it had no negative connotations.  It was used as we might use “inexpensive” today.  Goods were advertised for their exceptional cheapness.  Which, back in (say) Colonial American times, meant low price, not shoddy construction.

My point being that as long as I’m making a cheap and flimsy solar air heater, I might as well celebrate that.  No sense in trying to make a high-quality cheap and flimsy device.  Might as well make it as cheap and flimsy as possible.

Construction overview.

Solar air heater.
  • Make a big plastic tube out of a single sheet of clear plastic.  When flattened, roughly 4′ across by 16’+ feet long.
  • Place a 4′ wide piece of black or reflective plastic inside the tube, to form the inside bottom of the collector.
  • Stuff the tube, between the black/reflective plastic bottom and the clear plastic top, to a few inches depth, with a loose layer of dark, porous material.  I’m using mesh produce sacks, see below for other suggestions.
  • Leave 2′ empty, at either end of the tube, for attaching it to fan and duct.
  • “Quilt” the stuffed portion of the tube.  That is,  stitch through it with twine, or otherwise tack top to bottom, just enough that the top of the tube cannot “balloon” when the fan is turned on.  (The point of this is to force the air through the porous filler, not above it.)
  • OR, simply weigh down the top of the tube, with pieces of wood, to achieve the same end of keeping the top of the tube sitting firmly on the stuffing.
  • Tape the fan to one end, oriented to blow air into the tube.
  • Tape a piece of flexible dryer duct to the other end.

In pictures:

Plastic, about 8′ wide by about 20′ long.

Plastic sheet folded in half to make a long 4′ wide tube, then taped (see tape seam at left), with a 4′ wide piece of radiant barrier inside the tube to serve as the bottom.  I’m not even sure that radiant barrier (or equivalent piece of black plastic) is necessary.  FWIW I used Gorilla (r) duct tape, and that seems to be sticking well to the plastic sheet.

A bunch of mesh vegetable sacks drying in the sun, after being hosed off.  Why do I own these?  Long story.  But because I already owned them, I’m using this as my solar collector material, rather than black screening.

The plastic tube, now stuffed with those mesh sacks, balled up.  Try to pack it loosely, but with no voids that would let air flow around the mesh, rather than through the mesh.  You want to force the air to flow through the mesh so that it will pick up heat from the sun-exposed mesh.

Ready to run.  Fan is clipped into the near end, a piece of flex duct is clipped into the far end, and chunks of wood weigh down the top.  You can see that the top still balloons up a bit, between the pieces of wood, from the force of the fan.

The fan is an ancient twin-bladed window fan.  I’m guessing that with no resistance, it moves 250 CFM on low, and draws maybe 30 watts.  With the resistance imposed by passing through the mesh, I have no idea how many CFM it moves.

Same, side view.

Same, end view.

A nice stream of 129F air, at solar 3 PM, on an 80F day, with no adjustments?  That’ll do.

Total assembly time was around two hours.  And I now have a roll-up solar air heater that is adequate for the task of drying tomatoes.

Food dryer (TBD).

I am greatly simplifying my task by using Nesco food dryer trays.  With the addition of a bit of tape, these can be stacked to form an air-tight cylinder, with the food to be dried neatly laid out within that cylinder.  All I need to do is place that cylinder above an appropriately-sized hole in a cardboard box.  Run the flexible duct from the solar air heater into that box, and that will serve as the food dryer unit.

Note that with this design, the cardboard box itself doesn’t get wet.  All the humid air from the food goes up the stack of trays, and out.

 

Materials/tools list for the solar collector:

  • Pair of scissors.
  • Clear plastic sheet, approximately 8′ x 16′, or longer as desired.
  • Black or reflective plastic sheet, 4′ x 12′, or ditto.
  • Optional:  Additional clear plastic sheet 4′ x 16′, or ditto.
  • Dark, porous material to fill the tube (e.g., plastic screening, see below).
  • Tape (packing tape, duct tape, or whatnot).
  • Twine and something to use as a needle for “sewing” with that twine,
    • OR, double-stick tape.
    • OR four 8′ 2x4s.
  • Window fan or standard 20″ box fan.
    • Cardboard (e.g., 20″x20″ square) for modulating air flow from box fan.
  • Small length of flexible dryer duct.

Materials for the food dryer unit

  • Cardboard box
  • Nesco round drying trays (or substitute what you have).
  • Tape.
  • Cardboard sheet to cover the top of the stack of trays.
  • Instant-read thermometer.

Details

Step 0:  How big?

I’d like this to to produce around 900 watts of heat, on average, over an eight-hour sunny summer day, at 40 degrees north latitude.  Assuming this is 30% efficient at capturing sunlight, then, based on my prior calculations, this should capture an average of 18 watts per square foot.  So I’m shooting for about 50 square feet of collector.

I have no intuition as to the right shape.  I’m guessing that depends on a lot of factors.  The material I’m starting from is almost 20′ wide, so I’m tentatively planning on a tube about 4′ wide and 20′ long.  That’s a bit larger than necessary, but it matches what I have on hand.  Of that 20′, a couple of feet on either end will be used to connect to fan and duct, and so will not contribute much, if anything, to solar energy collection.

I’m guessing that one 8′ x 16′ piece of clear plastic sheet should be adequate to form the tube.  I’ll need a further 4′ x 16′ piece of black or reflective plastic to line the bottom of the tube.  And, optionally, one more piece of clear plastic, 4′ x 16′, to add to the top for “double glazing” of the finished, quilted tube.

Step 1:  Obtain a large amount of dark, porous, lightweight material.

In my case, that’s a box of mesh produce sacks that I’ve had on hand for years.  (These were part of a failed attempt to simplify the handling of my firewood.)

Plastic window screening should work fine, but is an expensive solution if you are using new materials, due to the amount of material required.

Or, you might try doing this with no filler.  Just blow air down a hollow clear-topped tube.  That should make this much less efficient at capturing sunlight.  So make the tube bigger than you would otherwise.

Beyond that, if you use something that isn’t compressible, you lose the ability to roll this up when you are done with it.  If you don’t value that, you could consider:

  • Styrofoam packing peanuts, painted black.
  • Coarse, dark, shredded wood mulch.
  • Possibly, lava rock.
Step 2:  Make a large plastic tube with a clear top and a black or reflective bottom.

This couldn’t be easier.  Get some clear plastic sheeting, e.g., the stuff they sell as dropcloths at the hardware store.  (In my case, I’m using greenhouse plastic, which is more UV-resistant than garden-variety hardware-store plastic sheeting.clear-topped plastic tube.)  Fold it in half, and tape the edges together.

I’m going for a reflective bottom because I own a roll of house-construction radiant barrier material.  The idea is that any light penetrating the layer of loose fill will get reflected back up into that loose fill.  And, where the fill is at least a half-inch away from the radiant barrier, the barrier will act as insulation against radiation heat loss through the back of the tube.

Step 3:  Stuff the tube — but NOT the last 2′ on either end — with a few inches’ thickness of dark, porous material.

For me, this was as simple as temporarily closing off one end of the tube, scrunching up the mesh sacks, chucking them inside, and using a stick to arrange them into a single, packed mass.

This isn’t precision work.  The air is going to flow through all 16′ of the tube.  As long as there’s no continuous channel through which the air can flow from end to end and bypass your porous material, you should be fine.

Step 4:  Keep the top of the tube from ballooning up.

You want air to pass through the porous filling, not above it.  So you want to keep the plastic top sheet right down on top of the filling, in some fashion.

I was originally going to “sew” or tape the top and bottom together in places, to do this.  But on reflection, the easiest thing to do is weight the top down, while obstructing as little light as possible.

I’m just going to toss some 2×4’s onto the top of the sheet, and, if necessary, weigh them down with (e.g.) bricks.

Optionally, add a second layer of “glazing” by tossing another clear plastic sheet on top of this.  That will trap insulating air where the top of the tube is depressed by the quilting or the 2x4s.  I’m guessing this isn’t worth it, but I make try adding it and taking it off to see what happens to the resulting air temperature.

Step 5:  Attach fan and duct.

Attach a window fan or 20″ box fan to one end, and a short length of flexible dryer vent to the other.

I want to be able to take this apart at the end of the season, to store it, so I’m doing these attachments with lengths of bungee cord.  You could just as easily make the attachments with tape, and peel back the tape at the end of the season.

Step 6:  Make and attach air distributor for food drying (TBD).

Because I’m using round Nesco trays, my air distributor will just be a box, somewhat larger than the trays, with holes for the dryer duct and the trays.  Run the dryer duct into the box.  Place a piece of cardboard on top of the uppermost tray, to make sure the hot air hits all the food as evenly as possible.  That’s it.

Step 7:  Operation.

Place the tube on the ground, in the sun.  Place weighs on top of the flat solar-collector tube, to keep the top from ballooning up.  Attach duct, fan, and (eventually) food drying box.  Turn on the fan.

Summary

It works.  And it’ll roll up at the end of the season.  So that’s a success.

This could use a bit of tweaking.

I probably used way more mesh “stuffing” than I really needed.  I can’t even see the reflective bottom of the solar air heater, through the green mesh bags stuffed inside.

I’m sure this would get hotter if I could tilt it so that it was perpendicular to the sun’s rays.  As one would do with a solar panel.

But … it works well enough as-is.  So I don’t see any need to modify it.  I can unroll it in the sun, attach small fan and duct, and produce a nice stream of hot air as long as the sun shines.  That’s really all I need it to do.

Arguably the most mickey-mouse aspect of this right now is the weights for the top.  Without those, the plastic sheeting simply balloons up, and the air passes over the mesh, not through the mesh.  Tossing some sticks on top makes it work, for now, but I’d like to get a more elegant solution at some point.

I’m now going to roll this up and put it away until my final crop of late-season tomatoes starts ripening in earnest.  Then I’m going to use this for a last batch or two of dried tomatoes.  Weather permitting.

Addendum:  Oh for duh!

Turn the fan around and stick it in the other end of the tube.

After I put this together, I went looking for a better fan.  Window fans of the sort I’m using really shouldn’t be used to push against considerable resistance. 

That’s when I realized that if I sucked air out of the tube, instead of blowing air into the tube, the entire problem of having the surface of the tube balloon up simply goes away.  All the wood and metal pieces on top of the solar air heater are unnecessary.  And I end up with a simpler and more elegant design.  If such a word can be applied to this cheap and flimsy roll-up solar air heater..