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Dave Blakey 05-12-2010 06:28 AM

Vermiculite mix
Hi All,
New to forum and am halfway through building oven in garden in Northumberland England. Next stage is to put insulation heatrh of vermiculite on top of base. Any advice on mix ratio and what best to put in mix.
Dave B

Glosta 05-14-2010 04:06 AM

Re: Vermiculite mix
Hello Dave B-I also just joined the forum. Building a 1st oven. I believe the site suggested a vermiculite 5:1 portland. I could be wrong. I used a 6:1 as an insulator an insulator around my chimney flue. Mix to an oatmeal consistency. If you use too much water the vermiculite starts to settle. So just add a little more dry ingredients. Good luck. Glosta

Dave Blakey 05-15-2010 12:07 AM

Re: Vermiculite mix
Hi Glosta, Thanks for reply and advice. Sun is shining up here, so will be mixing today. Dave

jota112233 05-15-2010 01:18 AM

Re: Vermiculite mix
I've seen some ratio's here as high as 10:1, but I went for a 6:1 and it seems to be fine.


Glosta 05-15-2010 03:33 AM

Re: Vermiculite mix
Serf-I like how you formed the vermiculite bed and concrete platform in one pour. Nice job. Did you use rebar in the bed? So what is your next step? I think it is laying down the fire brick oven tile floor--which I understand is laid dry & not mortared? In a fire place the firebrick floor is laid larger than the internal pit & the firebrick sides and and firebrick back are mortared on top. I guess this is to allow expansion of the fire brick hearth without breaking out the sidewalls? & just floats? Are you building a Pompei or Barrel oven? Good luck. Glosta

WoodchuckDad 05-15-2010 06:00 AM

Re: Vermiculite mix
I did mine last night. did about 7 1/2 to 1. I was surprised at the amount of water I needed to add.

jota112233 05-15-2010 03:08 PM

Re: Vermiculite mix
Hi Glosta - yep did use rebar. here's a couple of photo's of how I managed it.

Hope this helps


Dave Blakey 05-21-2010 10:47 AM

Re: Vermiculite mix
Hi Glosta, Finished laying vermiculite mix. Settled for 5:1 mix in the end. Set nice and firm. Now ready for laying oven floor. So many opinions on vaious sites of best way. Some say layer of fine sand some say few blobs of fire mortar under floor and level. which you doing? Anybody else have advice? Dave

Derkp 05-21-2010 11:37 AM

Re: Vermiculite mix

This is Derkp (Derk), I am just at the stage of pouring my hearth slab and have forms set up very similar to yours. Did you have any problems pouring the 1st layer and then adding the vermicrete forms and filling in around them? Any tricks you could suggest?


Glosta 05-23-2010 08:26 AM

Re: Vermiculite mix
I poured a four inch slab with 1/2 inch rebar six inches on center on top of 1/2 inch durarock/concrete board. The extra steel is to compensate for the four foot clear span over the wood storage area and span over the ash pit at the rear of oven. I am going to follow Jota112233/Jon's approach and form the interior insulating bed with 2X4 while leaving a concrete perimeter. Slab was screeded level. Will cut 100+ firebricks in half as preparation for the oven build and retreive the sand for leveling between the insulation layer and firebrick floor. However I wonder if we couldn't just use fine beach sand. The sand in my area, New England is silica dioxide. Although Portland cement volatilizes from the high oven heat, silica sand is melted for glass blowing & should survive the oven heat. The fire bricks are a mixture of silica dioxine and aluminum oxide. :o I will try to post a few photos later under my user name GLOSTA; but have no success this morning. Good luck. Glosta.

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