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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Just in case anyone is wondering about different plastic safety:

Happy crafting :)

JayallanB29 days ago
Im looking for a way to make a tridimensional chess board star trek style, would using plastic in this manner work for that. As far as sturdiness goes?
Im thinking if it turns out to rubbery it will just bend over and wouldnt hold the weight of the boards.

I'm no academic, just a simple soul who's interests are in environmental issues. I am responsible for loads of recycling and this idea of yours is very exciting. May I ask you to check what I intend to do.

Large pan with a little oil inside.

Place plastic bags in a metal loaf tin (greased.)

Place loaf tin in pan of oil.

Heat at 350 degrees until mushy.

Press plastic mush with weights.

Allow to cool in the loaf tin.

Is this right?

It seems fine to me. I would be careful about the plastic sticking, but if it's a low temperature then you'll be fine.

I am very interested in your process. What I would like to know is if you can make bigger items? I was thinking about making a small house or shed basically a work area out of the plastic. I know it will take a long time and I have that but what I need is how can I make a mold for the shapes I would like to use. Any idea???

Karen, just use a brick/clay mold. You can just take some scrap wood or plywood and tack it together, pour in your plastic. Just break the plastic out of the wood when you're done, or make large batches at once and take the cool solidifying plastic out of the mold before it dries completely. The key to building large structures is conformity in the Western world. Clay you can flex, plastic bricks, not so much!

Use the canola oil in a deep fat fryer as a double boiler to get the higher temperature, but no contact to the oil. Instead of a basket, use a thin walled aluminium sauce pan( better conductivity) shred the bags in a cheap shredder and dont worry abouy it overcooking if you have a thermostatically controlled fryer... Just let it sit for a while till it all melts together... ;)
awnal4 months ago
Hi. Id like to use this to make a foregrip and buttstock for a paintball fun wpuld this be durable enough to withstamd the force of being shot amd being held tightly while running and combat and thungs of the sort? And how do i shape it? Can i carve it down to size?
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 antioch2 years 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.
davejuniortwo7 months ago

can we use nay kind of plastic for this?

anything made of plastic


great stuff

ceknight6 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.
ac-dc ceknight6 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.
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.
mbear ac-dc2 years 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.
kirnex ceknight2 years ago
A pizza wheel or, best yet, a mezzaluna. I have one and use it for all sorts of crafty stuff.
pbilling5 months ago


Nov 17, 2014. 6:54 AM
Recycled HDPE bricks

Building bricks for housing using recycled HDPE sounds very interesting. To make it viable you'd need to do it on an industrial scale and have lots of plastic on hand. I don't know Bay island but if they are swimming in waste plastic then maybe. You'd also need to estimate the cost of the energy to heat the plastic. It is conceivable to build a large 3d printer that can directly print the walls of the house. I've seen some on the 'net only but they can print maybe single rooms I think around 14 feet in diameter (kinda like a plastic yurt). I wonder how you would have to coat the plastic to provide UV protection. An interesting set of problems. I wish you the best in this effort.

Starsword75 months ago

Great Idea, I love It. To make the wheel more uniform you could also clamp something circular on top of it while it is cooling.

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 /

hobotraveler > make homemade rocket stoves. Well tended fire is as efficient as a good stove. Melt your plastic and re-use.


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.

pdyson5 months ago

I think the best way to make this work would be to build a small rocket stove get a pan with a side tap use the tap open as to fill moulds and feed into HDPE threw the top of pan cannot see a need for any oil myself needs doing outdoors

pdyson5 months ago

just had a ten minute think about this one, can you not build a small rocket stove with a pan with a side tap on top so you just fill the pan with HDPE 2 inside it thus it will fall like a hopper as it melts threw the side tape into your mould? seems real simple to me without using oils

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.


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