Perlite insulation

I am planning on using perlite insulation under my earthen floor. Does anyone have experience with this material?

And by planning on using, I mean I just unloaded a semi truck full of it and it is sitting at my building site.

I have not used it, but I read up about it.
Here are some facts;
- Being so lightweight, perlite can be blown away and tends to float in excess water.
- Nonrenewable resource. ...
- Dust can create respiratory problems and eye irritation.
- It is used as insulation inside hollow brick walls.
- it drains easily and does not hold water

Scott Lawhead wrote:I am planning on using perlite insulation under my earthen floor. Does anyone have experience with this material?

The only experience i have is with my Rocket Mass Heater...  built the stove in my shop, fired it on and off for 2 or 3 years, and when i took it apart to lighten the shed for moving, found out that the perlite insulation had changed colour only half way throung the 6 inches of material that was in the stove.

The inside of the stove routinely hit 2,000 degrees, and the outside of the stove was always cold, so it does insulate.  Not sure how it would work under a slab at room temperature, with the possibility of exposure to moisture.

https://permies.com/t/40107/hot-barrel

Thanks for the input. I have many many super sacks of perlite to use under the earthen floor. Seems like a way better below grade insulation than polyisocyanurate.

And if I have any left over, it can go in the garden!

On another note, what do you folks do with empty super sacks?

I envy your supply of perlite. It's amazing stuff.

Regarding your sub-floor, I think the biggest concern is water incursion. Like any insulator, perlite provides tiny air spaces that slow the movement of heat from warm places to cold places. It also dries out readily, which is awesome. But if it is constantly wet, it provides essentially no insulation at all. So from my perspective, moisture management (from above and below) is pretty important in your design.

It worked! I now have about 14” of perlite underneath my floor, which is kind of a crazy amount. It was super dusty, and almost felt like swimming in a ball pit, but once road base was set down on it and compacted it turned into a super solid floor. A bit more expensive than foam for a similar r value, but… no foam insulation!

Love your perlite snowshoes!

What is the layer you put underneath?

I'll be interested to hear how it performs for you. Please keep us up to date.

The platform shoes were definitely necessary while leveling… it did compact more than we thought, we meant more roadbase on top of it (so.much.wheelbarrowing). There is 8” of drainage rock underneath it, with a commercial grade vapor/radon barrier between drainage rock and perlite.

It amazing, and unfortunate, that as many natural building systems one uses, it still comes down to a big sheet of plastic between the building and the earth, and a big sheet of plastic between the building and the sky. It’s debated on forums, but I think for longevity and reliability, a vapor barrier underground and a waterproof membrane on the roof is absolutely necessary.

Earthen floor is in a couple weeks! Need to install below grade plumbing lines and radiant tubes, but it’s close!

Scott Lawhead wrote:The platform shoes were definitely necessary while leveling… it did compact more than we thought, we meant more roadbase on top of it (so.much.wheelbarrowing). There is 8” of drainage rock underneath it, with a commercial grade vapor/radon barrier between drainage rock and perlite.

It amazing, and unfortunate, that as many natural building systems one uses, it still comes down to a big sheet of plastic between the building and the earth, and a big sheet of plastic between the building and the sky. It’s debated on forums, but I think for longevity and reliability, a vapor barrier underground and a waterproof membrane on the roof is absolutely necessary.

Earthen floor is in a couple weeks! Need to install below grade plumbing lines and radiant tubes, but it’s close!

One of the best uses of plastic I can think of. 50+ year lifespan vs the mere minutes that plastic dinnerware is used for.

I just got perlite insulation and see that you put the vapor barrier on top of your perlite.  I have two questions, does that mean you put the perlite directly above the gravel and then you put the vapor barrier on top of the perlite?  A lot of times in natural building, having something for the materials to grab onto seems essential (e.g. plaster on a cob wall or burlap, but not on bare wood).  Putting a base floor onto a vapor barrier seems counterintuitive.  Maybe gravity is holding it down?  So, were there any issues?  Cracking?  
Thanks,
Dimitri

The perlite is above the vapor barrier.

The layers are

Undisturbed earth
Drainage rock
Vapor barrier
Perlite
Road base
Earthen floor

How did you get it to tamp down level? I've only used perlite in a gardening context but it doesn't seem easy to compact.

Look at the "snowshoes"... pressing/tamping  with a big flat object keeps it from squishing up around the tool. He also mentioned that it settled more after the road base was installed, which makes sense as there  is only so much compaction you can do while the top layer is free to move around.

Glenn is correct. I actually avoided tamping it down. Insulation works because it is fluffy and has lots of air pockets, tamping would nullify those qualities. I used those silly snow shoes to level it to within 1” of where I wanted it to be; then I laid out a path of plywood to for me to wheelbarrow roadbase on top of the perlite. After 3-4” of roadbase, I ran a gas powered plate compactor, then another 3-4” of roadbase and the compactor again. Then ~2” earthen floor basecoat and a 1” finish coat. It’s about a 150,000 pound floor, all wheelbarrow by me. Great fun.

I did end up digging up a floor drain all the way down to the bottom of the perlite, and it was super firm, basically the density of polyiso “blue board” foam insulation. I did this right before the earthen base coat, after all the compacting and 1 year of working/walking/settling had taken place.

Amazing work Scott,

How is it performing?
What would you change?
Was digging the pipe later best or would you had preferred to have prepared pipe before?

I would be interested to hear what was done to source that amount of perlite. Were other types of volcanic rock considered for the project?