EPS-crete wall

First 10" of EPS-crete wall

I’ve got the EPS-crete wall started.  The forms come off today and they get moved up ready for the next layer.  So far, I’m liking both the process and the result.  It’s dead easy to mix, light to shovel, doesn’t require herculean forms and is easy to press into place.

The reinforcing wire isn’t necessary for EPS-crete used as post-and-beam infill, but the lower part of this wall will be backfilled for the first foot plus a bit, so the wire’s insurance.  When the foundation was poured I included old bolts, drill bits and big bent nails sticking up down the centerline to which the reinforcing wire has been fastened.  This is light duty construction.  The posts do all the “hold the building up” work.

Before I give you the mix recipe, here’s how I prepared the EPS for mixing.  You’ve already seen my foam shredder/grinder.  I transferred the ground EPS from the shredder box into tall kitchen garbage bags.  Into each bag I added between 2 and 3 pints of warm water to which I’ve added a squirt of dish soap.  The dish soap is a surfactant to break the surface tension on the EPS.  Mix the soap to water ratio as if you were planning to wash dishes with it.  Tie the top of the bag closed.  The bags I use have four “ears”.  I tie them diagonally in half-bows I can undo.  The goal is to keep the EPS and water/soap mix inside when I start rolling the bag around to distribute the soapy water.

The longer you can leave the mix in the bag (and even in the sun to help reduce the soapy water’s viscosity and allow it to spread) and the more times you can rotate it to get the liquid evenly distributed, the better the result.  Otherwise the water drains to the bottom without evenly coating the ground EPS.

The beauty of this method is, when it comes to the point where you’re mixing the EPS-crete, the ground foam is quite controllable.  It doesn’t float around, blow around or stick to anything via static electricity.  You can measure and mix it without getting it everywhere.  In other words, it ends up in the mix instead of all over you, the ground, the equipment, your other ingredients and your helpers.

Here’s the mix part.  Bear in mind this is subject to change based on how this wall  performs.

  • 2 parts cement
  • 2 parts sand
  • 1 part water
  • 1 part recycled latex paint
  • 16 parts ground EPS  (This is the most flexible part.  More or less depending on what you’re doing.)

I made my first batch in a cement mixer but it’s more work any way you look at it.  See my note at the end regarding using the mixer.  Lucky for me, our cement mixer stopped working after the first batch.  <wince>  The cement mixer came to us used with a history of being poorly maintained.    In addition to a new cord, the intermediate drive shaft needs rebushed and the central pinion (shaft fastening the barrel to the frame) needs replaced.    I’ll fix it but it’s going to be a major job I don’t want to make time for right now.

After losing the use of the cement mixer, Wadly mixed the remainder of the batches by hand.  It’s really easy to do using a short handled shovel.

For measuring, I’m using a plaster straight-sided plastic pitcher.  The shape, material and fact that it came pre-equipped with an integrated handle means the plastic pitcher works awesomely well.  It would be nice to have one for each type of ingredient.  Hmm.  It might be worth hitting the dollar store to see what I can find.

Because this recipe is by parts, it’s an easy recipe to duplicate.

  1. Give the bag of EPS a couple of flips to distribute any water that’s settled out.  Measure the ground EPS into the wheelbarrow, leveling it out.
  2. Sprinkle the sand over the top.
  3. Sprinkle the cement (be careful not to create dust and yes, you should be wearing a mask) over the top of that.
  4. Mix the latex paint and water together.  I use an old paint can to mix this in.  Stir thoroughly.  I should use a 5 gallon bucket and premix a whole bunch at once.  Next time.
  5. Drizzle the paint and water mix over the top.
  6. Shovel mix until everything is completely combined.  Watch for and break up any paint balls.  I would like to have a drill mounted stirrer for combining the paint and water to help avoid this problem.
  7. Shovel the mix into the form.  It’s fluffy so you’ll need to pack it in you will have voids in the project.  If one person shovels and one person packs, the work goes quickly.

I’ve combined ingredients in a different order but the steps above produce the best result.

This mix isn’t runny like regular cement.  It’s wet enough stay in place when you pack it into the form and not so wet as to have any of the parts separate out.  If you make it too wet, you’re doing two negatives things; you’re weakening the concrete and making it wet enough to allow the EPS to separate out.  You’re after a mix that’s wet enough to stick together when you pack it and dry enough to have zero slump.  If you try to pack it and it crumbles, it’s too dry.  If you pack it and moisture comes out ANYWHERE, it’s WAY too wet.  If your mix is too wet, reduce the amount of water you’re adding to the bags of eps.  If you reduce the amount you add when you’re mixing, you’ll get more paint balls.

From experience I’m going to say you will have to scrape the sides of the concrete mixer if that’s what you use to mix.  This stuff, because it’s so light, will stick to the sides and not mix thoroughly.  There’s not enough weight to the mix for it to scrape the sides of the mixer for you.  Be prepared to stop the mixer, scrape the sides and restart.  Success depends on thorough mixing.

Once the mix has set, spray it twice a day with water to help keep the cement hydrated so it will cure strong.

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