vermiculite insulation

[irelande5]

Hi all,

Having a hard time locating vermic locally, I did find some at Menards but it is the consistency of sawdust is this okay to use or should it be the size of peanuts thanks Patrick

[Gulf]

Re: vermiculite insulation

Have you tried any of your local plant nurseries. Many carry it in medium to course grade in usually 4 cubic feet bags.

[Neil2]

Re: vermiculite insulation

"but it is the consistency of sawdust"

You want something coarser than that. As Gulf suggest, try your local nurseries or lanscapers. Coarse grain pearlite will work as well.

[irelande5]

Re: vermiculite insulation

Thanks gents good call, just got back from nursery supply house, got 3 bags of course perlite, what kind of consistentcy do I need, thick or thin. Believe its 5 to 1, just don't know how much water to add, thanks again

[Neil2]

Re: vermiculite insulation

5:1 for under the oven. 12:1 for dome insulation.

Mix gently by hand, adding only enough water for workability. If water is running out and collecting in the bottom of your wheelbarrow than that is too much. Otherwise the water content is not too critical.

Once poured, keep the mix well supplied with water for at least 7 days and keep it covered with poly to hold the moisture in. You can start laying the floor as early as the next day.

[irelande5]

Re: vermiculite insulation

Thx Neil, this is for the oven top, already have the board for underneath, its 12 to 1 for top? I am also using 3 layers of blanket, probably over kill. Thanks again

[david s]

Re: vermiculite insulation

Be sure to allow the vermiculite to dry well before covering over it with stucco to prevent excess steam pressure build up cracking your outer shell.
Check my experiment on drying vermiculite slab attached.It illustrates how much water needs to be eliminated. You can do it all with fire but I find it easier to allow the sun and wind do most of the work. If done in one inch layers you can let each layer dry before proceeding to the next.
With three layers of blanket your vermiculite layer is really only needed to get the shape back, over all those folds and bumps, to a nice hemisphere so you can stucco over it neatly. I use 10:1 which makes it slightly more manageable to apply.

[Neil2]

Re: vermiculite insulation

"its 12 to 1 for top?"

Yes. That is what I used.

[david s]

Re: vermiculite insulation

Thanks gents good call, just got back from nursery supply house, got 3 bags of course perlite, what kind of consistentcy do I need, thick or thin. Believe its 5 to 1, just don't know how much water to add, thanks again

For every 10 parts vermiculite you need about 3 parts water, but if the vermiculite is fine it needs about 4 parts water. I guess every vermiculite batch is a bit different and the amount of water it contains would vary from the weather. Use the water left in the bottom of the bucket or barrow method. You can always just adjust it by adding a little more dry material.I don't know quite why, but I find a 50/50 mix of vermiculite and perlite makes a far more workable mix than either of them alone.

[irelande5]

Re: vermiculite insulation

Thanks David/Neil,

Just finished installing blanket and topping with perlite mixture, that was a messy job, there were areas I couldnt get it to stick well, mostly on the sides near the middle, but got good coverage on top. Just curious, how long should I let it dry before starting on stucco? How many fires and how hot/long would you recommend to help drive out the moisture/steam? I have done the 5 curing fires, though the last one I didnt let it get above 650f, want to go up to max heat slow as possible. Thanks again for all your help.

Nice work on documentation of you slab David!

[david s]

Re: vermiculite insulation

It is difficult to say how long you should wait before doing the stucco because the rate at which the stuff dries will vary as my experiment demonstrates. I don't really think that strength is an issue in the vermiculite layer because you only need it strong enough so you can stucco against it, so drying as soon as possible is the way to go IMO and as there is still lots of excess water in the layer it should be plenty to allow the hydration process. I've cracked a couple of outer shells from not drying the vermicrete layer sufficiently, so I'm now more careful to take it slower and longer. When the layer looks dry it will still have quite a lot of moisture in it. Try placing some sheet plastic over the vermicrete when you are firing. You will see condensation on the underside of the plastic if moisture is still present. Unfortunately because the blanket insulates so well, not too much heat gets into the vermicrete layer to assist drying. Just monitor the thing carefully and trust your own judgement. Good luck.

[Neil2]

Re: vermiculite insulation

"how long should I let it dry before starting on stucco?"

You want it to cure not dry. Allow seven days and keep the vermicrete well and continuously supplied with water. It needs water to cure.

[david s]

Re: vermiculite insulation

Whilst it's desirable to make the underfloor slab strong, curing it for a week makes sense, but the vermicrete/perlcrete layer only requires enough strength so you can stucco against it. That is part of the reason we use such a lean brew,we don't need strength. The other reason is of course to make it a more efficient insulator. If you end up adding more water to the layer after it has set, you end up having to remove most of it prior to stucco anyway. Apart from the surface there should be plenty of water retained in the grains of vermiculite/perlite for adequate hydration. (See results of my experiment).

[irelande5]

Re: vermiculite insulation

Hi Dave, when you stucco, did you just install over perlit/concrete, or did you prep surace at all? Thanks, Pat

[Neil2]

Re: vermiculite insulation

I would keep all concretes wet for at least a week. Vermiculite / cement is a type of concrete. You may as well get a reasonable amount of available strength from it.

Removing excess water after curing is, in my opinion, not that difficult.