Which vermiculite (fine or coarse pellets)

[sonomacast]

I wish to cast an insulated base over the concrete base using vermiculite, I see there are two grades, fine and pellets, Which is the better ( I am assuming Pellets would make a much stronger aggregate)
Also which grade would be better for the dome render (I assume fine would be easier to spread and finally what ratio, would it be the usual 5/1 mix. Thank you all

[Mingy]

Re: Which vermiculite (fine or coarse pellets)

I don't know which one is better, but I got the fine stuff, and man, its like water: I had put a couple 'drain holes' in my concrete base, so if any water got in it would drain out, and about half the vermiculite poured out of those holes before I realized what was going on! I frantically plugged up the holes, and eventually jammed window screen in to allow water to get out while keeping the vermiculite in.

It also ends up all over the place if there is any wind.

I wish I had used the coarse stuff ...

[Gulf]

Re: Which vermiculite (fine or coarse pellets)

I haven't seen vermiculite packaged with the exact wording "pellets". What I bought was labeled as "course". For the hearth, I poured a 5-1, but misfigured how much it would take. Pouring on a saturday, I was about 1/2 to 3/4 " short of filling the 4" form. The nursery (where I got the "course") closed at noon for the weekend. I had to finish with expensive "fine" grade horticulture vermiculite. (The "course" is the recomended grade for insulation.) I will say though, the fine grade used in a top coat for the hearth is highly workable and yeilds a cement slick finish.
I haven't got to the dome insulation yet but, I have seen from 8-1 to 10-1 recomended.

[david s]

Re: Which vermiculite (fine or coarse pellets)

I wish to cast an insulated base over the concrete base using vermiculite, I see there are two grades, fine and pellets, Which is the better ( I am assuming Pellets would make a much stronger aggregate)
Also which grade would be better for the dome render (I assume fine would be easier to spread and finally what ratio, would it be the usual 5/1 mix. Thank you all

I find that the finer grade is more workable in that it is less crumbly and you can therefore use less cement. However it also needs more water which has to be removed later and more water means more time for removal. For the mix over the dome I think 5:1 is way too rich. Remember that even a 10:1 mix uses the same mass of cement as vermiculite and increasing density, although increasing strength, decreases insulation value, so the less cement used the better. I discovered that a 50/50 mix of perlite and vermiculite makes an excellent mix with a lean cement addition. i.e. 5:5:1:3 vermiculite,perlite,portland cement, water. However the source of the materials available will differ depending where they come from so do your own tests.
Good luck, hope this helps.

[david s]

Re: Which vermiculite (fine or coarse pellets)

I don't know which one is better, but I got the fine stuff, and man, its like water: I had put a couple 'drain holes' in my concrete base, so if any water got in it would drain out, and about half the vermiculite poured out of those holes before I realized what was going on! I frantically plugged up the holes, and eventually jammed window screen in to allow water to get out while keeping the vermiculite in.

It also ends up all over the place if there is any wind.

I wish I had used the coarse stuff ...

If using drain holes, which is a really good idea, glue some fibreglass insect screen over the holes from the inside. Sorry, I suppose this advice is a bit late now.

[sonomacast]

Re: Which vermiculite (fine or coarse pellets)

Thanks all