Styrofoam Concrete




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.

There are many concrete projects, such as benches for sitting and walkway fill, that can be made using light-weight Styrofoam Concrete.  By substituting Styrofoam trash for store-bought gravel in the concrete mix, one saves on not only weight, but also on the cost of materials.  

To the best of my knowledge, Styrofoam is not a popular material for plastic recyclers.  Recycling it at home eliminates transportation costs for this bulky and low-value material. 

Many people don't own the property where they live, so maybe the incentive to build a castle for the owner over time is not there.  Instead of filling our dumps with this stuff, we could be building cities out of it, if we were motivated enough. 

I live on an island, and our dumps are filling up fast.  Taking waste and finding constructive uses for it is the best way to gracefully live with all the trash we generate. 

Styrofoam concrete probably has good thermal insulation, compared to rock concrete.  It might be a useful construction material in both hot and cold climates. 

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Step 1: An Early Experiment

This is a porous block of Styrofoam and cement.   By filing blocks of Styrofoam with special tool I made using lots of roofing tacks, I was able to make a supply of pea size particles. 

Using a soupy cement and water mix, I got the particles wet with the minimum amount of the mix needed to keep them stuck together.  By using the minimum amount of cement, the air space between the particles is not completely filled and the block is porous.  The block is fairly light weight.  It's strength is not what solid concrete would be, but sometimes the light mix is just fine for the job. 

I don't know what kind of uses this combination might have, but its porosity is interesting.  Perhaps, it could be a filter for air or water. 

Step 2: Another Experiment

This experiment uses a regular mix of sand, cement and water, and the porosity between the gravel-size particles is saturated with the mix.   The resulting concrete is stronger than the earlier experiment, but also heavier.

Step 3: Chunking Up Scrap Styrofoam

The city's recycling department used to save me sacks of Styrofoam packing material that people threw in the trash.  I made a hand-powered machine kind of like a tree limb chipper to rip it into smaller pieces. 

Basically, it had a hand crank at the end of a pipe shaft.  The shaft had some pretty wicked iron claws welded to it that dug into the foam that was fed into the machine.  The teeth went between parallel sections of rebar, which formed a comb-like grate in the floor of the bin.  The foam, caught between the claw teeth and the rebar got ripped to shreds and fell through the rebar grate to be caught in sacks below. 

Although I no longer have the complete machine, you can see what the claw shaft is like, and what is left of the wood hopper. 

Step 4: Bench Seat

This bench is made of Styrofoam concrete.  I used mostly Styrofoam packing peanuts to make it.  As the cement was hardening up, I found I was able to carve it easily with a sharp machete. 

''The "rocks" on either side of it are hollow "Trash Rocks", filled with some of my unrecyclable trash from years ago.  See my other instructable on trash rocks here:

Step 5: Sculpture Uses

Styrofoam in the cores of cement sculptures helps cut down on the weight a lot. 

This is a statue of my neighbor, Bartolo, emptying his coffee picking basket into a sack.  I donated it to the town many years ago and it is located near the plaza.  The armature is PVC pipe.  The rest is a combination of materials, but Styrofoam is a big part of it.  The reduced weight of this life-size cement sculpture allowed Bartolo, himself, to carry it quite a long distance from my house out to the road (just the figure, not the rock-like base, which was made on location). 

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    128 Discussions


    Question 3 months ago on Step 3

    I love your fake rocks. You mentioned they were porous. How do they hold up to the weather? In a climate where it gets colder, I would be concerned that the airspace could get waterlogged and freeze and expanding water would blow apart whatever had been created.

    I poured a wall at my house using straight concrete mix. I noticed my gloves that had become saturated were solid like rock the next day. So I threw some old pink fiberglass insulation in the mix as well. I figured the strands of shredded fiberglass would give it more strength.

    What ratio did you use? 1% portland, 3% sand, 3% styrofoam? I'm thinking 1-gallon bucket of portland, (3) 1-gallon buckets of sand, (20) 1-gallon buckets of styrofoam fluff, (5) 1-gallon buckets of shredded pink fiberglass insulation.

    1 answer

    Reply 3 months ago

    The fake rocks are sacks sewn of fishnet, filled with trash, with the fishnet then plastered with cement (1:3 mix cement to sand). If water gets in through a crack, it should hopefully find its way out through a crack, or you could drill drain holes in them. I have never noticed the rocks being full of water; definitely not enough to fill the whole rock. The insulation fiber sounds like a good idea, except for the possibility that the wet cement might react with it during curing. Some fibers, like basalt, need buffering by some chemical to protect them from the caustic cement while it is curing.

    If you don't know about basalt fiber products, check out basalt rebar on Youtube. It also comes in chopped fiber, twine, and cloth forms. From what I have seen, it is a stronger fiber than fiberglass is.


    6 months ago on Step 5

    that'absolutely brilliant and beautiful


    3 years ago

    Hyper Tufa, is mixing Portland cement "not concrete" together with peat moss for a light weight mix, makes great pots and bricks for garden borders. You can also mix concrete with pearlite to make a light but very insulated concrete slab. I used this mix for the cladding over the fire bricks on my bread oven. Build a fire inside and drag out the ashes, the oven stays very hot for days.

    2 replies

    Reply 6 months ago

    I've never had any luck with Hypertufa, no matter what recipe I use. It always falls apart when I pick it up.


    6 months ago on Step 2

    I've been making "fake rocks" with concrete and those styrofoam containers that you get with meat and fish from the grocery store. I simply cover foam piece with concrete using a trowel then, when it's dry about 12 hours later, I flip it over and continue to add concrete to the rest of the foam. I've made at least a dozen of these to use in what will eventually be my Zen garden to cover the clay and (expletive deleted) Johnson grass which is almost impossible to get rid of any other way. I first place recycled plastic bags that topsoil came in on top of the ground, then put the "fake rocks" on top. Eventually gravel will go on top of that. They're lighter than real rocks and do the job.

    "Styrofoam at the core of sculptures helps cut down on the weight a lot." This is what I was taught in a college sculpture class. Of course it's more complicated in that you have to place concrete lattice (the kind used to anchor concrete to the side of buildings) in order for the concrete to stick to the foam, and then you have to make sure that the thickness of the concrete is at least 1/2 inch or the stuff flakes off as has happened with one of my attempts at making a sculpture. (Now I have to go and "repair" the sculpture by adding more concrete.) (see pic attached of the "concrete Tori")

    Thanks for the idea about using styrofoam packing peanuts. I hate those things, but now I have a way to dispose of them and make something useful as well!


    9 years ago on Step 4

    the materials that make up concrete do not break back down to their original state. Effectively you're encapsulating something that takes tens of thousands of years to decompose with something that will not decompose for hundreds of thousands of years. What about using Cob? Although as a fully decomposable building material, using Styrofoam would effectively pollute it.... I suppose if you don't mind never getting rid of your cement construct it's a great idea- but if you want to do anything to it- you've pretty much made THE un-recyclable material for the ages. Albiet a constructive use of styrofoam. I would be interested in the structure changes Styrofoam makes to the concrete, if it significantly lessens the integrity of the material. If not, using it for housing foundations would be a good idea- they stick around for a long time and are easily reused. Cheers!

    8 replies

    Reply 9 years ago on Introduction

    Many of the piers along the coast of Southern California are made of gigantic styrofoam blocks encased in rebar cages and then covered with a thick layer of cement. I also seem to remember seeing something about freeform houses being made of a styrofoam substance shot onto a chickenwire frame and then coated with cement. Apparently the styrofoam does not affect the stuctural integrity of the cement. Environmentally, styrofoam may be a pain but chewing up trees to make plywood (which is probably as toxic as styrofoam) is not much better. I doubt that I would mix styrofoam chunks with cement because gravel is cheap and easy to come by. Besides that I favor smooth surfaces and styrofoam tends to float towards the top (even in cement).


    Reply 9 years ago on Step 4

    For me, it solves a little bit of the general recycling problem we all share by taking care of what comes to me. -- Gravel is cheap, and heavy to transport. Styrofoam trash is free. If we all sucked up what was local to us and built out of it, it could be a very sculptural material to build an interesting city out of. -- Well, I know it has some uses. I don't know its limits.


    Reply 9 years ago on Step 4

    I've actually got no problem with your use of styrofoam. I save a lot of the stuff myself and may try using it in a similar mannner for a couple of future projects like planter boxes and other garden things. Environmental considerations aside, styrofoam is everywhere, trash bins and landfills are full of it, it degrades slowly and there is no real way to get rid of it safely. Using it as fill material for sculptural cement is a novel idea but I would reduce the size of pieces to increase the overall strength of the material. The manufacturers of styrofoam packing parts and other items commonly run their "mistakes" through mechanical chippers connected to large collection bins or baghouses. That ground up styrofoam is then combined with unexpanded styrene balls in huge molds to produce styrofoam blocks that can be cut into slabs. The steam injected into the mold expands the new material and bonds the ground up materials into a single solid piece. Essentially you are doing the same thing but using cement as a binder. The larger the pieces are that you use the less structural integrity your finished product has, and if chunks of styrofoam are close to the surface there is the possibility that the cement will wear away and expose the styrofoam beneath. To avoid this, to ensure a better finish, and to improve the workability of the slurry I would run the styrofoam through some sort of chipper or leaf shreader to make smaller pieces. You could still use large blocks and chunks to build up the basic form, but then go with a finer ground mixture for the top coat. The finer ground slurry mixture would allow you to produce works with better detail capabilities and surface texture not possible with packing peanuts and large pieces. I imagine that you could mix a lot of of ground material with your cement before you reduced the quality of the surface or the sturctural intergrity of the finished work, but you would have to do some experimenting to find a good mix. I would not be afraid to use a three to one ratio to start with, but the smaller the styrofoam pieces, the better it will bind together and that equates to better detail and surface texture. Styrofoam may be an environmental disaster but there is a lot of it around, it is still being produced and that is not likely to stop any time soon. Finding alternatives to filling landfills with the stuff is a worthy pursuit and I think your idea is a pretty good starting place in that direction.


    Reply 1 year ago

    Hi mstar; I know it is sometime since you commented here. Wanted your take on using styrofoam and cement for a slab roof. We live in Jamaica and must use serious amts. of steel in our structures because of earthquakes. Would you suggest what ratios to use and what levels to pour the cement. Trying to use the styrofoam as a heat break in the slab roof and for it to be structurally sound. If you have some questions to gain clarity on what I trying to achieve, just ask. Hoping for a reply and thanks.


    Reply 3 years ago

    What would happen to the Kool-Aid Man if he tried to break into the city by running into the walls? OH YEAH!! :)


    Reply 9 years ago on Introduction

    Wow, What is it with you people? Before even thinking about what you are saying you jump right in with all of this politically correct rubbish. (Now that is one kind of trash that should never be recycled but unfortunately it does, again and again). However, you seem to want your cake and be able to eat it too. Is it not the aim of all responsible people to recycle rather than send to a land-fill? That aside, you are totally wrong on several other accounts too. Organic fill would not be readily prepared and would be fibrous and useless as an aggregate unless it was something like wood shavings but that would be next to impossible to get any kind of smooth finish. As to the material being unrecyclable, wrong again. If the author chose to get rid of the material, it is easily crushed and used again as an aggregate as now the styrofoam is encapsulated in the cement slurry rather than light pieces which are the real pollutants as they will be easily blown about the landscape. The real howler is your psuedo knowledge of construction. Light weight screeds have been used as floor screeds for a long time (such as Boral-Lytag which uses 'blown' particles of lightweight material as an aggregate) as they are a very good insulators, but something as light weight as this material could never be used as a foundation as it would crushed under the building weight but suitably moulded into blocks (a wooden box will do), this material could be used for internal, non-load bearing walls and it's texture would easily over-coat with a decorative finish.


    Reply 9 years ago on Step 4

    Old nylon-cement rubble and styrofoam-concrete rubble can all be used in road fills. -- To modify old structures with these materials is easy. The nylon-cement cuts easily with a cold chisel and a knife to cut the nylon. I have never broken up an old styrofoam-concrete structure, but I imagine all the old pieces could be mixed into a new batch of styrofoam-concrete and built with somewhere. -- The idea of the Termite Nest City, might be built using these materials. In such a city, very little of old structures would ever be demolished, since city growth is always upwards and outwards. Rubble would not be an issue.


    9 years ago on Introduction

    My company manufactures Styrofoam and concrete. There are additives you can add to the mix that promote the beads to mix more evenly. (I don't remember the names, and the names vary by country and market) As you all can imagine, until the concrete "wets" the beads, they are floating on top of the mix. (Problematic) One of the keys to a good mix is the mixer, which should be a slow pear type mixer that revolves the mix on itself (think bread dough). High speed mixers promote high shear, and this would destroy the Styrofoam beads. On a small scale this material works, but industrially speaking, there are better alternatives, including foams that are mixed with the concrete that leave large air bubbles in the mix.

    3 replies

    Reply 9 years ago on Introduction

    Thanks for the info. Mixing it with a shovel on the patio is the way I usually do it, but on a windy day that gets a little out of control since the Styrofoam weighs so little. I was making a hand-cranked mixer inside a plastic 55 gallon drum once, with mixing paddles attached to the crank shaft. I figured for light-weight concrete it might work, but I never got around to trying it.


    Reply 9 years ago on Introduction

    You might try plaster as well. If I recall, one could mix white glue with water, then pre-wet the eps (expanded poly styrene = Styrofoam) before adding it to the concrete mix. It all comes down to economics. We take in eps and add it to new block manufacture so we don't have any waste what so ever. You can also mix the eps with a solvent like Toluene and make glue. Or mix eps with styrene monomer to dissolve it and make other things. You can mix styrofoam with potting soil so it retains the moisture better. Styrofoam is a plastic that has many uses and creatively can be used for many things.


    Reply 9 years ago on Introduction

    Potting soil using Styrofoam particles in it is one thing that I could never understand. Other than on its surface, I don't think that plastic particles in the soil can retain much water. The little white particles always seemed cosmetic to me, just to make the potting soil look more special to the customer than it really was. -- What with the Pacific gyre garbage patch and plastic entering the food chain anyway, it seems odd to dump plastic into our gardens, on top of everything else. -- I have heard of disolving Styrofoam with gasoline and using it as a roof sealer. Do you know how that holds up under UV radiation? It sounds like a poor man's sealer, with health risks using it, though.