How to make insulating structural lightweight concrete using polystyrene beads : LUSENET : Countryside : One Thread

After just about living on the internet for two days I've learned how to mix and apply my own insulating concrete. There seems to be some interest from others on the forum so I thought I'd post it.

Concrete turns out to some really cool stuff, you can make anything with it, even boats(!) or canoes(!!). It turns out that there are a lot of companies that are making lightweight concrete, its nothing new at all and you can nail it, screw into it, even saw it with a hand saw. Lightweight concrete turned out to be a interesting coctail of stuff and you can mix it in thousands of different ways, the one below is maximized for insulating value with just enough strength to let it be a load bearing wall for 1 story, for stronger concrete with 2 storys remove 1 part beads or replace 1 part with construction sand. I guess you could also just make the bottom thicker and taper it up to the second story.

So, on to what I learned:

To make it you MUST have a rotary mixer to mix it right, otherwise what you will get inside the form is layer superstrong concrete on the bottom and a thick layer of weak beads on top. The beads have a extremely low density and tend to float up through the mix if your not careful. You can make your own mixer with a 55 gal drum, skateboard wheels, 2x4s, a long belt, a pulley and a hand crank or electric motor to attach to the pulley.

The mix (for a hundred pounds of dry-weight concrete):

70 lbs of Portland Type I cement.

30 lbs of Fly Ash (must-have else there are shrinking and strength problems)

[together the above two make up the total cementious material and are considered 1 part for volume calculations]

1/2 part sand

30 lbs of water. (there must only be 30% MAX by weight of water to cement ratio, too much water will ruin it, the fly ash reduces the water requirement a lot)

1 OZ of an Air Entraining Admixture (I have no idea what's in it, just know that it makes super small bubbles inside the concrete so when it freezes the water remaining inside the concrete can expand into these bubbles and not cause the concrete to spall [flake] or crack)

4 parts by volume of expanded polystyrene beads

Place dry ingredients ONLY in mixer and mix for 5 mins, 1 rotation of the drum every 2 or 3 seconds, MAKE SURE YOU PUT A COVER ON THE OPENING OF THE MIXER - else the fly ash will billow out and its nasty stuff to breathe. The idea here is to score and roughen the surface of the beads to let the cement attach to it otherwise they might float up to the top of the mix.

slowly pour water into mixer, mix until ingredients are thoroughly mixed and concrete is plastic (about 5 mins)

pour into form (in wx above 50 degrees F), there should be structural reinforcments inside the form like rebar, wire mesh, steel pipe, etc. Dont use galvanized steel, it reacts with the cement and forms gas bubbles that inhibit adhesion to the steel and therefore strength.

Let sit until soft cured (cured enough to maintain own shape), the concrete needs to retain the water inside it to cure correctly which can be lost through surface evaporation, since putting it under water isnt practical for most people - either keep it moist with a spray, soaker hose, wet burlap sacks, etc. Or wet sacks and enclose your new concrete with plastic sheeting for a few days. It will attain structural strength in about 3 days, and most of its full strength in 28 days, depending on weather conditions. Concrete gets stronger the older it gets over years as the chemical reactions continue within it. You can put another form full of concrete on it in about a day and a half, again depending on weather.

Its best to do forms that are around 4 foot high (dont know why)

This mix will give you concrete that is about 60 lbs per cubic foot, with a compression strength of around 600 - 700 lbs/sq in. In comparison wood has a compression strength of 350 - 600 lbs/sq in perpendicular against the grain, 1400 lbs/sq in with the grain. Regular concrete has a compression strength of about 4000 lbs/sq in (depending on mix).

This concrete has an R value of about 1 to 1.1 per inch, in comparison wood studs have a R value of .9 per inch, regular concrete an R value of .08/in , Polystyrene Bead Board an R value of 3.57/in.

Dont use solvent based penetrating sealers on this concrete, they can melt the beads and ruin the finish. Water based penetrating sealers are readily available. The concrete is almost totally waterproof.

It can be nailed, sawn, screwed, filed, etc, just like wood.

You can also use a material called Perlite or Vericulite (sp?) as the aggregate, strength goes up, but insulating factor goes down.

This concrete is classified as a Class A fire resistant material with a resistance of 5 hours for 8 inches of concrete.

Footings have to be full strength rebar-reinforced concrete and at least twice as wide and thick as the wall its supporting.

Walls should be at least 8 inches thick for one story, (my barn/garage is going to have 12 in thick walls), I wish I had found out about this stuff a long time ago, it would have saved me a bundle in insulating the basement. My barn is going to have 2 inch black pipe in a pattern kind of like this: |/|\|/|\| embedded in it along with the wire mech for added strength and shear resistance to earthquakes.

This stuff is so versatile from now on everything I build here is going to be concrete! As soon as I can get the materials Im going to mix up a batch, pour it into a 2in by 2in by 2 foot mold and test it, I have no idea how though how to test the compression strength though. If somebody makes it before me please let me know.

Whew, Long one! Hope this helps


-- Dave (AK) (, May 05, 2000


Thanks for the leg work could you email me with some web sites to follow up on Shaun

-- shaun cornish (, May 05, 2000.

Oh man, I must have quite literally gone through 150 different web sites, the bonanza was when I did a Web Ferret (it hits about a dozen different search engines) search on "Lightweight concrete bead" and I just started going through them one by one. I also did searchs on and Lycos

Give me a couple of days to retrace my steps and Ill post the sites and pages I hit, or I can email them to you directly.

-- Dave (AK) (, May 05, 2000.

Dave thanks again I can tell it took a lot of time and trouble to do all that research! 6 of 1 1/2 dozen of the other but I think a lot of Us would like to know were to get more ( and you already gave Us alot) information. Your right cement is cool stuff Edison did a lot in the early 1900's IE a single pour house with furnitur and all thanks Shaun

-- shaun cornish (, May 05, 2000.

Thanks, DAVE, VERY interesting! Just what I like, information, how to, data! When you go back and find some of your best or favorite web sites on building with concrete or concrete with things in it such as foad beads or sawdust or whatever, would you please post the sites?

Again, I for one, am very interested and I know others are, too!

-- Elizabeth Petofi (, May 05, 2000.

I did some web-surfing, and found info on sawdust cement. In fact, the article I remembered originally (without pictures) is up on the Web at Sawdust, Sand and Cement. For those who may be metrically challenged, rough approximations are 300 millimetres=30 centimetres=1 foot, and 25 millimetres=1 inch.

I also found other information - for instance, much North American sawdust is fairly acid, and needs the addition of lime to neutralise it. However, I'll leave others to search out the information relevant to them, if the subject is of any interest at all. I found the above, and much else, by using Google and searching on the term "sawdust cement". I use a few search engines, mostly multiple-submission ones that call on many others. Some good ones (easy to use too) are:

Ask Jeeves
Inference Find

Dave, just a thought: a lot of packing material these days is foam things - in shape like worms or corn-chips or hollow hemispheres or just about anything. For most people that stuff is just a nuisance once the package is opened. It might be worth your while seeing if that stuff is readily available, and if so running a trial with it - straight and in conjunction with the foam beads. You might need to break it down a little - it's generally bigger than the standard beads, but it could be a cheap source if it works. Another - would breaking-up foam boxes provide something acceptable? How about packing material and broken-up boxes mixed? If not for all the walls, how about just the tops of the walls, or above doors or windows, or maybe even below window frames?

-- Don Armstrong (, May 07, 2000.

Here is a partial listing of the sites that I used to gather my information, I cant find again all of the sites that I used, but it has the essentials. You might have to convert from metric though. practice.html,1149,'article_ar chive~search_article_archive',00.asp (search for lightweight concrete bead)

Unfortuneatly I cant find the a post I stumbled on in a professional construction forum that said you can get away with not putting a aqueous dispertion of polyvinal propionate for proper dispertion and adhesion of the beads by dry mixing the beads for five mins in a rotary mixer and using a cement mixture that is lean on water.


You probably could use the styrofoam peanut packing material and shredded up solid styrofoam as your aggregate, but one of the posts I read said you should use virgin beads so it adheres properly, it was also said that the beads should be fairly small to maximize bead surface area.

Hope this helps too, I actually had a lot of fun learning about concrete and I just scratched the surface, there are a lot of people out there that are so smart about this stuff its almost scary :-)


-- Dave (AK) (, May 07, 2000.


For those of you that want to try the PVP anyway, a company called BST makes a product called AGRIMER. (Polyvinylpyrrolidone (PVP)) for agricultural use.

-- Dave (AK) (, May 07, 2000.

Another thought, or trick I just remembered my brother talking about a cousin using. He was building pig pens, concreting the floor. He laid a layer of beer bottles in the concrete, holding them down somehow - with mesh? The trapped air was insulation from the cold ground, the volume saved cement, and doing it that way was at least a defensible reason for emptying the bottles - and you couldn't waste the contents now, could you?

-- Don Armstrong (, May 08, 2000.


Are you aware of a product called RASTRA block? The blocks are concrete forms made of cement and recycled (they claim) polystyrene beads. They are manufactured in Mexico. Quite a few homes on the west coast have been built using this material. I believe is their site. I haven't checked out the source sites for your article as yet; I assume they include where to buy the beads and other ingredients.

I never ceased to be amazed at what one can find on the net. I couldn't have programmed at a better article. I too would like to make insulating concrete.



-- Charles Stirling (, January 16, 2001.

Man-o-man masons must be retarded because it appears no one in this newsgroup knows the metric system!

-- George (, April 29, 2001.

Dave, thanks for all the data, and the time you spent researching this product.

I've always been interested in insulating concrete, and this is the first "hard" data I've seen. I've seen lots of CLAIMS about how wonderful different types of insulating concrete were, but no actual numbers.

I love concrete as a building material. My place is all concrete and steel filled split faced, dyed, concrete blocks downstairs. if my other place hadn't sold so soon after we put it on the market, I had planned to do pure concrete and steel walls, and do a fancy finish on the outside with various types of small pebbles and what not.

Have you crunched any numbers on cost of the stuff you describe? Here in Southern Oregon, we use insulation with R-19 (minimum) on up. I usually use R-25 or so. To get this much insulation with the insulating concrete would require walls some 20 inches thick. i wonder if it wouldn't be cheaper and stronger to just pour a six or eight inch concrete wall, then insulate either with expanded polystyrene (R 5 per inch, m/l), or do as I did, and put a 2x3 studwall inside the concrete wall, for mounting fiberglass insulation and for running wires and pipes.

I do like the idea of the recycled foam pellets, though.

My concern about strength is that pure, "regular" concrete is supposed to be only about the same as a wood framed house as far as earthquake resistance (yes, I live on the west coast). By weakening the concrete with the insulation, it looks like you'd be making wall that would be much heavier (at 20 inches thick), adding a lot of mass, without a proportionately greater strength.

If I were serious about this, as you seem to be, why hot pour a piece of concrete, complete with steel, say four feet long, six inches thick, and a foot wide. Put the ends on solid supports, after it's set up. Then load it up in the center, and see how much weight it takes to break the two types. I suspect the "regular" concrete will require well over 1000 pounds to break, and I'd sure be interested in how much weight the insulated type would hold.

Good luck!


-- jumpoff joe (, April 30, 2001.

Found an interesting site on lightweight concrete and other structural applications.

Best regards


-- Drobar (, May 16, 2001.


Thanks for the posting. I found this while doing a search for Expanded polystyrene beads.

Now the question I have is: What is your source for the beads. I am looking for a commercial sourcethat has a very good price.

I recently returned form France where I was documenting ferrocement houses for an ongoing project I am doing at the Ferrocement Educational Network.

These specific houses are double shell ferrocement with a lightweight concrete pumped into the cavity for insulation.

The formula given to me which I have not tried yet is this:

Portland Cement[any type] - 1 cu. meter [250 Kilograms]

EPS beads, 2-3 mm diameter - 1cu. meter note: weight of beads is listed at 14 Kilograms/ cu. meter

1/4 liter dish detergent

100-125 liters of water

The dry ingredients are addes first then water and soap.

The individual batches were 1/5 of the above listed formula and was mixed until homogenous, in a vertical mixer with a sweep arm that rotated around a central vertical shaft.

I don't know the RPM of the mixer but I suspect it was slow.

This mixture is not load bearing. After mixing it was then pumped directly from the mixer into the double ferrocement walls.

What type of mixer did you use?

If you or anyone else is interested in ferrocement you can go to [website always under construction] for more information.

I have also set up an e-mail ferrocement discussion group that cna be joined form that site. Although ferrocement is the main tp[ic of discussion other alt. const. techniques and methods are discussed also.

The discussion group is free.

Dave and others, please reply to my e-mail address at as I do not monitor this group [although perhaps I should] and only found it by chance.

Thank you all,

Paul Sarnstrom

-- Paul Sarnstrom (, May 30, 2001.

How much concrete will this make? How big is a part (for volume calculations)?

-- ted (, July 17, 2001.


I happened upon your site while doing a search for "how to build your own cement mixer". I've read through the information provided. Is there any way you could email me the specifics for your design? My husband and I are building our own stone house in the foothills of Maine. Any help would be greatly appreciated.

By the way, thanks for all of the great information you have posted.


-- kelly mccrillis (, July 23, 2001.

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