Can insulating concrete be exposed to the weather?

[Alan]

It's the first week of October here in south central PA - 3 weeks or so until the first frost. Our Casa 90 is up on the stand, the brick landing is partially in place, the arch is in layout, and we've changed our minds from gabled house to igloo. So my questions:

- Does the insulating concrete for the igloo need to be put in place and shaped in one day? I'm thinking that the answer is "no" especially if I leave it rough where I left off.

- If I don't get stucco on the outside before the cold weather arrives, will the insulating concrete make it through the winter, or do I need to plan some kind of temporary protection? Is perlite or vermiculite better in this regard?

[maver]

I think both perlite and vermiculite are used in gardening to retain moisture in the soil - exposed insulating cement is likely to absorb quite a bit of water over a winter. Ideally stucco before the frost, but a tarp or other cover would do fine. Mine is a gable style so I did not use insulating concrete on top but I bet it's a lot easier to apply it over a couple days to allow the lower coverage to firm up before applying more mass on top.

[james]

I would agree with Maver. A vermiculite/perlite concrete would absorb a lot of water. Not the end of the world, and it won't decompose, but I think it is worth the effort of putting up a good tarp. I think that would be time well invested -- in that it will save you more time and hassle later trying to dry everything out and worry about where the moisture would go it you finished the Igloo over it.

As a complete aside, we had our roof off for a home extension during a huge storm a few years ago. High winds blew the tarps off and water flooded into the house. And there I was with lightening coming down in the pour rain, on the roof trying to hook the tarps back down. Ah, memories.
James

[Alan]

I've seen reference somewhere to building a stucco or plaster shell over a pencil rebar frame and dry filling with vermiculite. If rough coat stucco is at all like refaractory mortar then it would mold like clay (but perhaps sag in the absence of something to draw out excess moisture). Is the insulating concrete approach taken because it's been found to be easier?

[Scott Welker]

Exposed insulating concrete does gather water

And should never be used as the permanent outermost coat of your oven. I have a dome that I stuccoed, with a stucco heavy in latex to repel water. Any water-repelling solution will work.

Now the water won't harm your oven directly, but if you build a big fire after a heavy rain the water the vermiculite/perlite/pumus will expand and possibly crack! Yikes, that would be terrible. Well, you'd have to patch it.

So what the other posters said is right on the money...cover with a tarp until a permanent solution becomes available. Stucco and gabled house are the two most common, but indoor ovens need none of that, they're protected from water by a "house".

Happy baking

Scott

[Scott Welker]

Multi day application of the insu-concrete works fine

In fact it took me months (chagrin).

Scott