TRASH ROCKS -- Eliminate Unrecyclable Trash




About: I'm a refugee from Los Angeles, living in backwoods Puerto Rico for about 35 years now and loving it. I built my own home from discarded nylon fishnet and cement.

To make a trash rock, a sack is first sewn out of fishnet.  It is filled with trash and plastered with cement.  The resulting shells are unique in shape and look very natural.  Trash rocks are an esthetically pleasing and constructive way to eliminate trash.

Trash rocks can be used as benches, tables, sculpture bases, landscape accents, and walls. A family living in one location over time could build a castle out of their trash. I would expect trash rocks to have good thermal insulation, useful in both hot and cold climates.

I'm big into recycling and built my whole house out of recycled nylon fishnet and cement, a material I call nylon-cement. For many years I eliminated all my trash right at home using trash rocks. 

Ideally, I would like to see a chemist develop a way to recycle some of our plastic trash and make a mesh material like fishnet out of it that could be plastered with cement. 

Recycling is all about mining trash; converting waste into something useful. If we separate our trash first and put it into separate trash rocks we would know where to look for specific recyclable materials in the future when we need them.  In the meantime, why not enjoy living around all the trash we generate? 

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Step 1: Scoring the Fishnet

Many years ago I bought new fishnet by mail from a fishnet manufacturer. That seemed fairly expensive at the time; $6 a pound, I believe. I wouldn't be surprised if it is double that now, or more.

Then I found the free fishnet mother load of all time right under my nose, the StarKist tuna factory. They were very helpful to me in saving used fishnet that the boats wanted to get rid of. Discarded netting is a trash disposal problem for the factory, so we helped each other out.

After getting it home, the fishnet was opened out, cleaned off, rolled up and stored outdoors. It smelled "fishy". Given a month or two of exposure to rain and air it was completely user-friendly. Fortunately, I live in the country, where I can do this without offending the noses of neighbors.

Good luck finding a source of your own. Fishing ports and fish farms are good places to start looking for used fishnet. Ready-made trash sacks that can be plastered with cement should be available for this idea to really take off. Sewing your own sacks allows you to make different sizes of trash rocks, but ready-made sacks would save some time and effort. This is a link to manufacturers of fishnet. Most are in the Orient. A search for "netting" on Thomasnet can come up with U.S. manufacturers.

Step 2: Sewing the Sacks

Sew the sacks however big you want your trash rocks to be. I made my own super-sized curved sewing needle out of heavy wire. Hammer one end of the wire flat and drill a hole in it to make the eye of the needle. Make a rounded point at the other end.

I use nylon twine to do the stitching with. When protected from sunlight by the cement, nylon will last a long time.

Step 3: Fill the Sack

Fill the sack with your trash that nobody wants to recycle. Use twine and the big sewing needle to sew the mouth of the sack closed.

Step 4: Site Preparation

Depending on where your trash rock is going, you may have to prepare the site. In order for new cement to stick well to old cement, the old cement has to be clean. A pressure washer works great for cleaning cement. Throw down some cement before placing the trash-filled sack in order to adhere the new rock to the old.

If you are putting the trash rock on the ground, you might want to dig a little nest for the trash rock to sit in. Throw some cement in the hole before setting the sack of trash in it. That gives you some foundation, and might prevent animals from burrowing up into the trash from underneath.

As with building any rock wall, keep in mind how the next row of rocks will sit on the row you are working on. Plan ahead to avoid problems.

Step 5: Mixing the Cement

The normal cement mix for plastering is one part cement to three parts sand. 1, 2, 3 is an easy way to remember it.

(The same 1, 2, 3 will help you remember how to mix concrete: one part cement, two parts sand, three parts gravel. )

You can mix small amounts of cement in containers, or in a wheelbarrow. I usually mix a sack at a time on a patio area with a square end shovel.

To do that, mix the dry materials first. Then shape the pile like a volcano and add water to the hole in the middle. Mix it and add more water if needed. Try not to add too much water. It is easier to add more water later than it is to patch up a too juicy mix with more dry material.

Depending on the size of the mesh of the fishnet you are using, you might want to have the mix be drier or wetter. Larger mesh might accept a drier mix, where a thinner mix would fall through the holes. With fine mesh, you might want a wetter mix for better penetration.

Step 6: Plastering the Sack

After dragging the sack of trash to the location you want your rock, and setting it in a bit of cement, the best way to plaster it is usually from the bottom up, with vertical strokes of the trowel, but there are exceptions to every rule.

When you stroke upward, the trowel makes a sort of "V" shaped pocket in which the cement on the trowel rests. If you stroke downward the "V" is upside-down and the cement tends to fall on the ground. After the cement is up, it can be stroked in different directions without much problem.

You might want to brush the surface of the cement after it starts to harden up some, in order to knock off any sharp bumps that might interfere with plastering the next layer, or applying the color coat. Quite often, to get adequate thickness, you have to plaster the rock twice. The second coat is easier, because the first coat is solid at that time.

Step 7: Colorizing

Cement can be painted, or colorized by adding pigments to the cement. Paint tends to weather away, chip, and blister. When the pigments are part of the cement, colors are more permanent.  Powdered pigments for colorizing cement are available in hardware stores. 

Pigments, powdered or liquid, can be added to the cement used in plastering the trash rocks. Pigments cost money, though. Less pigment is used if plastering is done with uncolored cement and a thin layer of colorized cement is then brushed onto the surface. That is what I usually do.

When exposed to sun and rain cement will slowly wear away. The thicker the pigmented layer, the longer it will last. Colorized cement can be brushed on with a broom head or big house brush. One can also fling cement from a brush to create irregular spotty effects.

Exposed to the weather, even un-pigmented cement can become beautifully colorized by nature as algae grows on it.

I haven't colorized any trash rocks yet, but this photo shows colored cement effects on the wall of a house.  I added some concrete acrylic fortifier to the cement to hopefully make it more weather resistant. 

Step 8: Trash Rocks I Have Known

These are some trash rocks I have made over the years. 

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    56 Discussions


    4 months ago

    I expected the sand to be less grainy and more contained as a lump because of which there is lot of after play mess to clean up as it doesn't stick to itself as mentioned. Apart from that my kids are enjoying the product.Very good quality and grip. Both have nice chiseled and yet non sharp edges which helps a lot. Though a didn't buy it solely for quilling and yes they haven't disappointed at all.


    3 years ago

    Hey! That's a whole house built with waste rocks of glass botles. Located in Morretes, Parana State, Brazil. "Pousada Itupava" for net searching engine... It pays a visit. Bottles were collected from waste thrown, by tourists, into Nhundiaquara River.
    A place to stay some days and look the landscapes, and get into the rivers... But the waste rocks house is particularly beautiful to stay into, make some pics, and speak about its building with Mister Ibrahim, the owner. Fantastic!


    5 years ago on Introduction

    Great details!

    For me personally I wonder if I'd just be passing off the problem to my children's children, just like the national debt. I watched the movie Wall-E and saw mountains of trash bricks in that vision of the future. A 3D printer seems a better way to use up trash plastic and reduce the purchase of new plastic products at the same time. It's not a solution for everybody though, so make- make- MAKE what you can!

    4 replies

    Reply 5 years ago on Introduction

    How does a 3D printer use up trash plastic? I got one recently and it uses new rolls of plastic filament to make things. What I need is a home machine that makes filament rolls from trash plastic, and I don't see that on the market yet.

    My trash rock idea does put the problem on hold, hopefully indefinitely in permanent construction. If we are smart, we would separate our trash first, so our children's children know which rocks to mine for clear glass, for example, or various plastics in the future when we are more hard up for used materials.

    I mostly see the printers making novelty toys, or decorative oddities; things we don't really need -- generating more mountains of plastic to get rid of eventually. They can maybe make a cell phone case, but they don't include the electronics that go in it.


    Reply 3 years ago

    Sorry to get back to you so late Thinkenstein:
    The 3D printer using recycled plastic solution to (some) trash is based on the make your own filament machine plans on the net. Depending on the grade of plastic, there are grinder/extruder machines to be built which recycle trash plastics into filament for 3D printing. Hope this helps, I apologize for not having a nice Google search string ready for you.


    Reply 3 years ago

    The make your own filament idea is good. I wish one could make plastic rebar and plasterable mesh material for cement work, too.


    Reply 5 years ago on Introduction

    Don't we just keep building over urban areas anyway. What is the difference between building over this and great urban areas built over older layers. I really like this idea. Save the gas to haul it to the dump, the landfill space itself, and it isn't like these materials couldn't be reclaimed as I am sure the elements will break down the and maybe by then we will have better recycling programs in place. We have none where I live.


    4 years ago on Introduction

    Not a castle, but I have an insulated workshop in mind. Outer wall and inner wall 8" apart made of steel mesh to be plastered in cement and use trash for the fill. The fill isn't load bearing but I'm going for thermal mass and it's got to be cheaper to use cardboard and plastic refuse rather than portland cement.

    We are all just waiting to be compost. Our trash is all just waiting to contaminate the environment, since it may outlast us. We encyst nuclear waste in containers to protect us from it -- for a little while at least. Encysting our trash is a similar strategy. The longer it stays encysted, and useful as fill inside our construction the better the situation for us and the environment, I would say.

    One problem with recycling is that it is not always profitable for someone to recycle things. In our system, nobody puts more energy into recycling materials than it is worth to them, so we will always have piles of useless crap building up. I take my useless crap and build with it, even if only as fill material.

    The city doesn't really want to haul it away. Our dump is full, and we have to pay another city to take it. That city's dump is filling up rapidly. I live on an island and. Islands have limited dump space. Project far enough into the future and we have an archaeologist's paradise, but a bad life support system.

    Got any better strategies?


    5 years ago on Introduction

    I live in a neighboorhood were most families put out a 250 liter trash bin every other week and a 250 liter greenbin the other week.
    still have the old 140 liter trash bin and I last year I put that out twice rather than 26 times. My greenbin I NEVER put out... I have a garden


    I have found out that my nearby Wal-Mart sells nylon netting at about $1 a yard. Given the fact that my college doesnt recycle a LOT of plastic bottles, i think i might have a way to test my island plans!

    2 replies

    Reply 6 years ago on Introduction

    Please tell me what department that would be in. Fishing? Fabrics? I want to try making some trash rocks and don't have immediate access to fish nets.
    Thank you

    I take it you think of making a floating island. I have heard of a guy in Mexico who did that on some lake. I don't know if you could get away with that in the states. I hope the bottles don't just escape into the water eventually.

    Thinking of the Pacific garbage patch, it would be nice if there was some sort of floating recycling plant that could turn the trash into plasterable mesh trash bags and plastic boats to float float it back to civilization.

    Some chemistry student could do big help in the plastic trash problem if he could figure out how to convert plastic trash into mesh material that could be plastered.


    7 years ago on Step 8

    Man, this is some neat stuff you've made here! Do you think an island could be made out of this stuff, depending on the methods and materials used?

    4 replies

    Reply 7 years ago on Step 8

    I made a floating cement trash rock once, filled with sealed plastic bottles. I suppose you could make a floating island, or one that rests on the bottom.


    Reply 6 years ago on Step 8

    Also regarding the floating trash rock, what would your opinion be on making one thats in the shape of a boat hull? if the right amount of bottles were used, it could be done, yeah?


    Reply 6 years ago on Step 8

    It would float, like a regular bottle raft. Without a skin over it, though, there would be a lot of turbulence in the surface area -- not like knifing through the water with a solid hull. It would be a boat shaped raft is all.

    what if you added a few bottles and some cardboard to give it an angled keel along the bottom of the hull? Depending on how it would be fashioned, the fishnet would have to be cut in a pattern to cover the entirety of the boat itself.