Plastic Smithing: How To Make your own HDPE Plastic Anything (DIY plastic lumber)

Picture of Plastic Smithing: How To Make your own HDPE Plastic Anything (DIY plastic lumber)
How to make really good hard plastic while reusing and recycling plastic bags at home! Via this method, you can make ANYTHING you want to, out of hard, lightweight, real plastic that's astoundingly durable. It comes out very similar in texture to recycled plastic lumber.

best of all, this method involves no fumes!

I'm gonna show you how to make plastic wheels for your robot!

I first heard about stewing plastic bags to make new things from Dave Huebsch's book " Village Assignment " about interesting adventures had while running a charity/NGO (" Common Hope ") in Guatemala. He, amazingly, repaired the bottom weight-carrying main bearing of a washing machine with a big plastic disc made of stewed plastic bags, which actually was such a good stand-in replacement that it held up for several years. (and here are some more Guatemalan Handy Tricks)

I had to try it right away, and the first couple times I just burnt plastic, until I came up with this method.

By the end of this, you'll be able to make yourself a knife sheath, mold around your shoes and make DIY hard-toe sneakers, wheels, bearings, bushings, or any kind of plastic part! Take pictures and post them in the comments!
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A lot of guessing going on in the comments.

I have found that HDPE (code 2) and polypropylene (code 5) both melt non-toxically in an electric oven set to 180-210 degrees celsius - it varies quite bit between samples. It cools quickly, so you have to work fast to mould it, it is soft but not fluid at those temps.

can we use nay kind of plastic for this?

anything made of plastic

normally i just melt plastic items like bags, pens, and unwanted things with lighters and turn it into something useful. the only problem is that theses alot of smoke and the smell of it hurts

babycody2 years ago
I am in to vacuum forming plastic. However the sheets are not cheap. Has anyone experimented with making sheets out of thermoforming plastic such as milk jugs? I work at a company that uses pelleted plastic, and I really want to try this technique on some of those pellets. I have read around 80 comments so far, but have not seen anyone mention using a deep fryer with a temperature control. Does anyone see a drawback to using one?

Hi babycody, I just saw your question about thermoforming plastic such as milk jugs. I used to love to play with this stuff. It melts between 350 and 400 F dry oven temp. It stays pliable for about 10 minutes if you want to stretch or trim it. I've also melted layers into bread pans for door stops. Once it has melted at high temps and cooled, it will not melt again so be sure of the form or melt at lower temps. Once it gets to the liquid state, work with it quickly to press into forms. It reacts to cool air to harded in as little as 5 minutes. Other ways I've worked with it is cutting it into the shapes and soften the edges with a bic lighter.

i haven't tried it out yet but maybe too much oil. if it's a deep fryer with a basket you will need quite some oil in it to establish contact with the bags.

and another possibility would be the risk of molten plastic bits falling or seeping through the basket. thus either creating a bit of a mess or disintegrating the whole block.
mbear antioch1 year ago
From what others have said in the comments, you can use a deep fryer but you'd probably want to put it in another container of some sort to contain the plastic bags. Something like an empty coffee or soda can.

My theoretical process:
1. Put some oil in the can to act as a mold release agent. Swirl around edges to get good coverage.
2. Put shredded plastic bags into can.
3. Put can into (cold) deep fryer. (If oil gets in the can this is apparently OK.)
4. Turn on deep fryer and set to target temperature.
5. Profit!

No idea if it'll work, but at least it's a start.
hobotraveler7 months ago

Hello, I am in Kara, Togo West Africa, trying to stop malaria in this city of 100,000. The root cause is plastic bags that block the drainage canals, and rivers, making dams that allow mosquitoes to lay larvae. Presently, the locals burn some of the plastic bags, but never enough. This pollutes, and burning plastic cannot be healthy. I would love to have the same process done using mirrors, or to make some form of solar concentrator that melts the plastic down into manageable size. Then maybe we can make hoe handles, or shovel handles from the plastic, if really good we could make roof rafters. How to use mirrors to concentrate on plastic oven cheap? I think an oven melts plastic different than putting onto a burner. Andy Lee Graham / hoboontheroad AT /

You could have a look at something like this

no need for electricity then :)

HoboTraveller, you most certainly CAN concentrate enough solar to do this.
One way would be to use a dish shaped frame (such as an old style dish antenna) and attach the mirrors to it - they would generally focus on the dish's central point, put a pot full of plastic there and, I dunno, a metal funnel at the bottom? It'll probably burn from time to time but should work.
Another way might be to use the focusing screens off of large TVs that have been thrown out.

You can find instructions for these kinds of large solar devices, just look for fun terms like "solar death ray" and the like.

mmohesky7 months ago
Will it work with a pan instead? We don't have any pots to spare.
sypage10 months ago
About how many plastic grocery bags would you estimate it took to make that disk?
augapfel11 months ago
I'd probably try to shred the plastic bags and bottles in either a blender or a paper shredder or maybe a food processor so I started with a rather uniform raw material.

I'd also probably use a potato masher instead of a fork to really blend and mash the gooey plastic into a more uniform and consistent blob.

Finally as it sounds like forming the plastic into the mold is a challenge I'd probably heat the mold. I think I'd place it in the basket of a steamer and use the butt of a small screwdriver or a wooden dowel or a pestle to pack the plastic goo into the mold and press out any air.
stasterisk (author)  augapfel11 months ago
cool can you let me know how your experiments turn out?
um_dustin1 year ago
Bear with me... Have you tried melting on the stove just to homogeonize the plastics, then using a double-boiler in the overn to melt the plastics into a rough form that only needs minimal cleanup?
By the way, this is my e-mail add. You can suggest something but very specific and general about the question. I'll wait for it.
I'll just ask if these plastics can turned into a jelly-like or a silicon-like object that seems to be a cellphone gel cover? But it doesn't mean that it should turn into a CELLPHONE cover. I just need it for our research. You can answer me through my yahoo mail.
tenpcrisps5 years ago
so it didnt melt the plastic container? you just put it in there and it was fine?
I am not a expert but the plastic would lose a lot of it heat very quickly which is why you have to move fast to get it into the mold. It also would depend on the melting point of the mold you are using. Also not all of the heat from the plastic is moving to the mold. It should if you leave it alone come to the average temperature of the plastic being molded and the mold. That is not counting how much heat is lost to the air.
I am wondering this too. Should the plastic "mold" be ice cold or coated with more oil as a release agent?
ceknight5 years ago
Best way to shred the plastic better would be to put the bags in a large Rubbermaid type trash can and go to town with them using a weedwhacker. Just be prepared to spend some time untangling some of the shreds from the whacker head.
A pizza wheel or, best yet, a mezzaluna. I have one and use it for all sorts of crafty stuff.
ac-dc ceknight5 years ago
Odds are what would happen then is the bags get wrapped around the head, pulled tightly into the bearing, melting and ruining it.
countable ac-dc5 years ago
Or get a second hand document shredder and feed the bags through that?
ac-dc countable5 years ago
A document shredder might also get plastic wrapped around it's cutting wheels, they are best used for materials that aren't easily stretched. Earlier I proposed a method to more fully melt these bags, that it be done in a covered (metal) container so they can be heated higher to their melting point without bursting into flames because no air (oxygen) can get to them. If they are heated to full melting point there is no need to shred them, then can just be compacted (to melt faster, they would melt either way) by placing something of weight over them, like a piece of metal, glass, etc, something you don't mind ruining by coating with melted plastic or that you wil reuse for the same task in the future. However it is not very necessary, with a covered container the internal air temp rises much more than an open container so plastic will melt faster regardless of whether in direct contact with the hot sides of the metal container it's placed in to heat it.
mbear ac-dc1 year ago
I wonder if you can get around that by putting the bags in the freezer for a few hours. I imagine they'd be more likely to snap instead of stretch, and they'd obviously be cooler so heat may not be as much of an issue.
stasterisk (author)  ac-dc5 years ago
I ran some bags through a hand-cranked paper shredder, it worked fine.
Great, but that is a fairly random point of information, we can assume most people don't have the same hand-cranked paper shredder you do. Generally speaking, this is a senseless instructable. There is zero need to shred bags, it's all nonsense. The only thing needed is to keep oxygen from getting to the bags while they are heated enough to melt, no shredding at all is needed, no shredding at all is the slightest bit helpful. ALL that is needed is for the temperature to be controlled so they don't ignite while being heated to their melting point, OR for the vessel they're in to be covered so if they are heated beyond their flash point, there is no oxygen to allow them to ignite. I fail to understand how instrucables can ignore such basic science. It's madness actually, all the crazy things that happen when we ignore the basic principles of chemistry.
Honestly I think it is your comments that are the "fairly random points of information"! Fair enough point that most people these days would most likely have an electric shredder rather that a hand one but the point being; they both shred paper don't they so in theory they will both shred plastic, the main catch (literally) is that if the blades aren't sharp, then you have the possibility of the plastic wrapping around the cutters. And as for the covered pan, for there to be little or no oxygen in there the pan would have to be sealed with a vacuum. Even if the plastic was in a pan the was sealed with a vacuum you can still run the risk of ruining the plastic by burn or charing the plastic. I agree that the theory is there no oxygen, no flame; only problem being that there are a multitude of things that could ruin you project not counting the devastation of a naked flame.
Then you'd be wrong Samson41thermal. You cannot just start throwing plastic bags into an electric paper shredder, the pieces will wrap around the blades and possibly ruin it. As for the covered pan, no you don't need a vacuum to remove 100% of the oxygen, you only need to remove enough that it does not support continued combustion. I have done it as described. It worked fine and the result was superior. No you do not run the risk of ruining the plastic (but what do we really care it was just leftover bags??) because it won't significantly burn or char without sufficient oxygen present. This is basic chemistry, all one has to do is pay attention to the details and not be insane about it (heat the plastic to a reasonable temp rather than a very excessive one). To say there are a multitude of things that could ruin it is beside the point, the same is true of walking down the street and chewing gum at the same time. It's really, really simple. You're just trying to argue for argument's sake. Heat the plastic in a covered container, as airtight as possible but not with such a rigid seal that it would allow a pressure buildup to a dangerous level. In other words a coffee can with a metal plate on top works fine. The bags do not need to be especially shredded, not shredded at all actually they can just be wadded up into a tight mass at the bottom of the can. Simply heat this with a low even temperature (if the can is large enough a stove burner will do, or a fire, or whatever is convenient for the location and method you prefer for handling a heated can and pouring melted plastic... most people probably won't want to do it in the kitchen in case they spill any. Perhaps this is the biggest factor, melted plastic will make a mess if spilled, just like anything else liquid would too but it may ruin what it spills on so having the right work area is prudent. As for the results it is no contest. Molten plastic poured into a mold makes as good a part as the mold is good. Just be sure you use a release agent like silicone spray so you can easily get the part out later. I wouldn't say the part is quite industrial quality but leaps and bounds better than only a compressed mass of small shreds. Maybe a project doesn't need this amount of durability or quality, but for the sake of completeness it is good to contrast other alternatives and let people decide for themselves.
Fair enough point about the shredder, I may be wrong and yes you may have melted the plastic in a covered pan successfully. I am the first to admit I don't have any sort of chemistry degree or anything of that sort, but I am a chef by trade and I can tell you that a covered pan with oil in it can end up smoking and you run the risk of a fat fire. The reason this can happen is from things like solids in the oil or contaminants in the pan.
spartandude5 years ago
A water filled pressure cooker would work to melt this. You must have a pressure of 29.82 psi (will give you a constant 250 °F). This is actual pressure not gauge. To adjust for actual pressure from a gauge reading add your ambient air pressure to the gauge reading. There are a few ways to get your ambient air pressure (since it changes with elevation): 1) A. look up your elevation (google maps, etc.) B. look up atmospheric pressure on an elevation table. C. calculate. 2) A. Measure temperature of boiling water. B. Look up corresponding pressure in water tables. 3) experiment. To change pressure in a typical pressure cooker add or remove weight from the vent. You can also get an approximation of the gauge pressure by measuring the weight of the blow off valve, measuring the area of the tube it sits on then calculate the PSI. Sorry if this is too complex, but I hope it helps. Peace.
Please don't ever play with or alter the pressure release device (vent) on a boiler, hot water heater or pressure cooker. They are designed to prevent catastrophic failure of the pressure vessel. At one atmosphere pressure the volume will expand 16,000 times upon sudden pressure release. That would be like instantly having 16,000 pressure cookers full of hot vapor in your room and there would be no room for you, so you would end up elsewhere. (look up specific volume in steam tables)
signed Second Class Stationary Engineer - play safe everyone:)
jaggdlynx1 year ago
Has anybody that's tried this with the oil method found a process for cleaning / degreasing it, to a degree suitable for painting? I love this idea, and am just wondering if the plastic itself ABSORBS the oil, to where it will remain sort of oily (never to be capable of adhering paint), or if it is possible to scrub off the oil on the outer face, use some form of adhesion promoter of plastic primer, and finish with a longstanding paint job?
How slippery is the end result? I want to use this to make a plastic outdoor basketball/ volleyball/ soccer surface.
vreinkymov2 years ago
Has anyone else tried doing this with mineral oil? It ends up eating away the polyethylene and turning it into something like petroleum jelly.
greenminded3 years ago
I entered a winning idea which is similar to the discussion here. See idea posted entry number 4 : by Mary Jean Netario Cruz

Blocks of Hope

"Plastic Pollution is one of the major reasons of the last years “Ondoy” disaster that put Metro Manila under a devastating flood. In spite of this horrible experience it has been noticed that drainage and floodways continued to be clogged by plastics. An enterprising solution must have to be achieved to recycle and make money out of this garbage. These plastics can be made into blocks where in it can be used to build a shelter. Other use is it can be made into furniture, just like how lego works. An electric block machine has to be designed, either for every home use or for cooperative to process the used plastic into a block. Each block will be sold to the one who build the house or create the furniture using the blocks as one of its major materials. These manufacturers or engineers will design a system where all they have to do is to be like a kiddo playing creation from lego toys. These blocks will be mainly to be used as walls, tables chairs or depending on the block per part design basis. This will solve problems of the plastics and generate income for the household."

Can anyone help me on technical side for my business plan preparation?  Deadline is on Jan 29, 2011.  For those who can help me, please email me at
All you really need for that is an electric oven (or other kind of oven if electricity is available, you just need to be able to control the temperature precisely and keep impurities out) and a compression mold in a shape similar to a lego brick (pegs on one side, holes on the other). You make the side-walls on the mold taller than the finished block will be thick so that you can overfill the mold slightly. Put it in the oven and heat it up until the plastic is thoroughly melted, then put the top plate of the mold in and crank it down. The top plate should have relief holes to let the air out. Once you stop getting air and start getting plastic, you screw some plugs into the holes, and then put some more pressure on the mold just to make sure it all sticks together well. If you use a consistent weight of plastic every time and crank it down to a fixed point, you should be able to get a reasonably consistently sized block.

The advantage to this method over a dedicated, integrated machine is that you can make such molds relatively cheaply out of local materials (even scrap) and operate them with any heating method capable of generating 350F. (An aluminum foil solar reflector can generate that kind of temperature pretty easily in sunny areas.)

The disadvantage is that it will take more human labour to operate. But that should be offset by the fact that a machine capable of reliably molding non-consistent plastic waste into consistent sized blocks would be rather expensive to build, while a human of average intelligence can probably learn the skill in an hour or two. Most of the labour will be going and collecting the plastic waste anyway. If you have something simple like this it is practically indestructible then you can let random strangers bring in plastic they've collected and rent an oven and a few molds without having to worry about them accidentally feeding something hazardous into an expensive machine.
Well plastic could be used as an aggregate filler in cement ;and can be shredded, melted down and custom molded for decorative moulding and mill work and other architectural uses . i understand that you want to use it as a major material in construction and you are right to think so. it is strong and reliable and some types of plastics will not breakdown for a very very very long time. my self being a construction worker and occasional tinkerer of sorts i think plastics is a viable construction material worth exploiting.
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