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morrishuckeba 07-15-2010 01:27 PM

:mad:I have a question on insulating the dome. I am using the ratio of 1 to 10 of vermiculite and with that mixture Iím having trouble getting it to stay on the dome. It seems to be very crumbly and hard to work with. Do you have to let it set up overnight and then add more? If you have any suggestions please let me know.:confused:

Neil2 07-15-2010 01:38 PM

Re: vermiculite
Go up in 6 inch "lifts". Allow to set for an hour or so. The next lift then rests on the lift below.

david s 07-15-2010 10:02 PM

Re: vermiculite
Make sure that you mix the correct amount of water with it ie for every 10L vermiculite add 1L cement powder and 3L water. Mix it really well and work from the bottom up making sure you leave a ledge to hold the next lift. Also pressing and holding the mix in place for a couple of seconds helps. It seems like the mix won't hold but it does set up firm enough to take the outside stucco.

turkey 07-16-2010 01:59 AM

Re: vermiculite
dont people alot use mesh to give it something to grip into for the first layer?

dmun 07-16-2010 05:33 AM

Re: vermiculite

dont people alot use mesh to give it something to grip into for the first layer?
It won't stick to mesh. It's not like mortar. It's like stacking up oatmeal. As Neil says, you have to do it in courses, giving a while for the previous layer to dry, or the whole mess will collapse in a heap.

morrishuckeba 07-16-2010 07:45 AM

Re: vermiculite
It is like pushing a car up a hill with a rope.

Dolf 07-16-2010 08:52 AM

Re: vermiculite
Will it be much worse insulating when mixed 1:5 for instance?

david s 07-16-2010 06:13 PM

Re: vermiculite
A1:5 mix will set up better, but you are adding heaps more weight to the resulting mixture, increasing its density and hence reducing its insulation value. I usually cover the whole dome in one go,with a layer about 35 mm thick, leave it for a few days so nature will do most of the job of removing the water, then do a second layer. Tapping with the flat of a trowel will give you a perfectly formed hemisphere.

Dolf 07-17-2010 03:12 AM

Re: vermiculite
Thanks, I will definitely go weaker then. A tad worried now as I did my floor 1:5. While that is lower & thus less prone to heat leak, I am also worried for another reason. I use 2nd hand bricks which are very!! hard (8 cuts per diamond blade :-() so I used a build-soldiers-on-floor approach so as to get away with chisel break ends only. Problem comes in that I have casted my vermiculite in a circle within a concrete border and the excess length and corners of the floor bricks which are "sticking out" the soldier outer circumference is now resting on the concrete floor! Thus small ends not insulated at all. In my enthusiasm at the time & focussing on starting round & first encounter with fire clay etc (which hid the outer perimeter & thus allowed me to forget), so no excuse other than neglect at the time, but now 5odd rows up, its too late to redo.
On the positive side, I see many entrances not insulated to a big degree, so perhaps the loss to the lower & outer fringes may be little enough to get by.
Unfair to ask for anybody with such experience as you guys all do it right, but I am somewhat concerned.

david s 07-17-2010 03:51 AM

Re: vermiculite
Don't worry you'll be ok. You won't lose too much heat from those bricks in contact with the concrete. You are also correct with the floor mix. It needs to be about 5:1 for the strength required as it supports the floor and dome. I was referring to the mix (10:1) over the dome.

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