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kebwi 09-21-2009 07:54 AM

Vermiculite/perlite confusion
During my initial research I found the super expensive bags of vermiculite and perlite at Lowes. They were in transparent bags so I could see what they looked like and I remember them being gray and rather large in granularity, several mm if I recall.

Then I found a super cheap source of perlite at a masonry store and this morning bought three 4 ft^3 bags without a second thought (I anticipate using five or six eventually). This stuff was much whiter, ivory perhaps. More to the point, it is much finer than the stuff I saw at Lowes. It looks like laundry detergent, grain size of half a mm perhaps? My concern is that smaller grains might pack tighter, leaving less "fluff", less air, and weaker insulation.

Are there different types of perlite and did I get the wrong kind? The bag even lists insulation as a possible application, so that gives me hope.

My final decision for perlite over vermiculite was based on the facts that it is the cheaper of the two and reportedly has a slightly higher insulative R value.

Shouldn't I want something with large grains so it will pack loose with large air pockets? Is this a vermiculite/perlite distinction (which implies that I am not remembering the appearance of the perlite at Lowes accurately) or does perlite come in different grain sizes...and would I be correct in assuming I want the largest grains possible for the loosest fill?

BTW, my application will most likely be concrete, not loose fill, since I'm doing a dome, not an enclosure, although I am considering the approach of a rebar-chicken-wire stucco dome with a dead space around the brick dome and filling it with loose fill as opposed to concrete, haven't decided yet. Obviously, the hearth is concrete either way.

Thanks a lot.

dpike 09-21-2009 12:50 PM

Re: Vermiculite/perlite confusion
i found the fine stuff did not create a very good layer, as it became one with the concrete and was not oatmeal-ish enough. So i tore it out. This vermiculite was from McClendon's. The good, coarse grained, setup well, and looked just like oatmeal vermiculite came from DeYoung's in Woodville.

kebwi 09-21-2009 12:56 PM

Re: Vermiculite/perlite confusion
Thanks. Rats. Thought I was set up on this. It was only $15.40 a bag at Salmon Bay in Ballard (pretty near where I live in Lake City).

EDIT: Actually, I just called DeYoungs and their prices are $26.98 vermiculite, $15.98 perlite, so effectively identical to Salmon Bay for perlite.

Thanks again.

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