Vermiculite not seeming to stick to chicken wire/fireblanket

[paul600rr]

Hi just starting to put my vermiculite mix over my chickenwire/fire blanket ive started off with a thin layer but seems like it wants to always fall out at back of dome at base for some reason and start topull chicken away from blanket I'm using a 5:1:1 mix vermiculite cement hydrated lime any advice to try get it to stick better stronger mix or change whats in it cheers Paul

[UtahBeehiver]

It is tricky stuff to work with 5-1 is typically under the floor bricks with 8-10 to 1 for the dome. You cannot do too much or thick at once or it slumps. I made a curved trowel and only did 3" lifts at a time.

[david s]

Hi just starting to put my vermiculite mix over my chickenwire/fire blanket ive started off with a thin layer but seems like it wants to always fall out at back of dome at base for some reason and start topull chicken away from blanket I'm using a 5:1:1 mix vermiculite cement hydrated lime any advice to try get it to stick better stronger mix or change whats in it cheers Paul

Skip the lime but a little (a handful for every litre of cement does help a lot to make it hold together better. Adding more cement just increases its conductivity which in turn reduces its insulating capacity. (see the table Russell posted previously)

Another important factor is to get the water content right. Too much water will wash the cement off the grains and too little makes it crumbly. Diffferent grades of vermiculite require diferent amounts of water. The finer the grade the more water you will require. When mixing, combine the dry ingredients in a barrow with a spade then add water slowly while mixing until the water just pools a little in the bottom of the barrow. Continue folding in the mix and the grains will absorb that little water in the bottom, or add a little more dry material.

Another trick to avoid collapse is to build up the wall from the base abot 6" and leave it for 24 hrs. It will be firm enough to build higher without risk of collapse. Doing this allows you to carve away any bits that are left proud and gives you an idea of the materials strength. Any hollows can also be easily filled with the subsequent mix.
Once the wall starts to lean in as you go higher it becomes far easier. Make sure you wear rubber gloves or your hands will regret it the next day.

[paul600rr]

Skip the lime but a little (a handful for every litre of cement does help a lot to make it hold together better. Adding more cement just increases its conductivity which in turn reduces its insulating capacity. (see the table Russell posted previously)

Another important factor is to get the water content right. Too much water will wash the cement off the grains and too little makes it crumbly. Diffferent grades of vermiculite require diferent amounts of water. The finer the grade the more water you will require. When mixing, combine the dry ingredients in a barrow with a spade then add water slowly while mixing until the water just pools a little in the bottom of the barrow. Continue folding in the mix and the grains will absorb that little water in the bottom, or add a little more dry material.

Another trick to avoid collapse is to build up the wall from the base abot 6" and leave it for 24 hrs. It will be firm enough to build higher without risk of collapse. Doing this allows you to carve away any bits that are left proud and gives you an idea of the materials strength. Any hollows can also be easily filled with the subsequent mix.
Once the wall starts to lean in as you go higher it becomes far easier. Make sure you wear rubber gloves or your hands will regret it the next day.

David vermiculite going on better thanks I'm thinking for the 2nd coat to swap over to perlite as granules smaller think that be easier to work with will that be ok no issues you see ??? Cheers Paul

[david s]

Actually I've found a mix of both perlite and vermiculite works better than either of them alone. I use half medium grade perlite and half fine vermiculite.

[paul600rr]

I was going to finish last coat in pure perlite buy a bag think it help me get done ready better for rendering as I’ve nearly ran of vermiculite safes bags 2 bags thanks for your help assume perlite be similar ratio 6:1 ish

[david s]

No, if you want it to insulate it’s better to make it leaner. Because it is not supporting weight it only needs to be strong enough as a substrate for the outer render/stucco layer. Look at the table Russell posted for strength:insulating value. If you have 3” of insulating blanket, you may not be so concerned about the perlcrete/vermicrete insulating layer. I use 10:1 ratio which produces about the same as insulating blanket (for equivalent thickness) and is strong enough to act as a firm substrate. Going any leaner makes application more difficult.
I just finished a 35mm insulating layer four days ago. The job took me 2 hrs. Now waiting for it to dry in the sun and wind before a series of drying fires.

[david s]

After 6 days of drying (no rain) I did some drying internally too, I completed the render layer today then wrapped the whole thing in cling wrap to enhance the strength of the outer shell.