vermiculite/portland and weather

[jnpe]

I will be ready to add insulation to my slab in a few days for my WFO here in southwest VA and have a question re. vermiculite/Portland.

Is this mixture weather resistant? I plan to extend the insulation past the edges of the dome but I am concerned about exposure in that area to the elements. Will it wick moisture under the dome and lose insulating value? Should it be waterproofed?

Thanks

[Jed]

Re: vermiculite/portland and weather

Hey Jnpe,

I can't say I remember any conversation about this question in the past, but here are my two cents on the subject...

The vermiculite / Portland cement mixture is a very porous product. It will absorb water.

It would certainly hold water andwhen it gets wet it will wick the water through the full structure. And if you live where it will freeze, the frozen water will break up the structure created by the Portland cement.

I think if you want your structure to last, you will cover the exposed vermicultie / Portland insulation with tile, or stone or some product that will protect this insulation from the weather and keep it dry.

JED

[dmun]

Re: vermiculite/portland and weather

Those builders who take their vermiculite concrete out to the edge of the support slab usually cover it with whatever surface treatment they use for the stand/structure be it stucco, tile, stone or brick face, etc.

It's not recommended to leave your insulation open to the weather.

[jnpe]

Re: vermiculite/portland and weather

Thanks for the replies!

Most good thermal insulators by design have a high degree of porosity and just wanted to make sure I wasn?t missing something re. verm./port. Encapsulating the exposed edges with stucco sounds like a reasonable approach and planning to proceed that way.

Found one bag of #8 vermiculite locally and have ordered the remainder.

Thanks Again
Joe

[cvdukes]

Re: vermiculite/portland and weather

Definitely don't leave the vermiculite mixture exposed to the weather! See my post from last year about failed attempt to use it as a roofing material. It will continue to sorb moisture if not weatherproofed... then it will freeze and chip off in small chunks.