Vermiculite + sand as floor bedding material

[shanxk8]

Quick question, rather than adding to my ongoing build thread. My v/p-crete has cured and i'm pleased with the result and hoping to finish cutting & start laying my cooking floor soon. I've ordered myself Heat Stop dry mortar for building my dome & expect it to arrive before the weekend. In part this was because I was having difficulty finding fireclay, which brings me to my question.

The plans and most of the discussion I have found through searching indicate that wet fireclay and sand is the recommended bedding material to level the cooking floor. I have a bunch of vermiculite left over from my v/p-crete insulation, and am wondering if I could use the vermiculite (possibly with sand) as a bedding material under the cooking floor?

[UtahBeehiver]

How level is your p/v crete? If you are level the you can skip this step, the sand/fireclay is really only for leveling proposes. With vermiculite particle size by impact ability to level small amounts. You might be better with a wet sand mix put on with a notched trowell if you need any leveling. IMHO

[shanxk8]

I thought i had levelled & smoothed out the p/v-crete well. It is a rather bumpy surface but thought it would be "flat". It seems to have "shrunk" a little down from the form so the form sticks up at the side.

I laid out my bricks to test on the p/v-crete yesterday, and using my selected bricks with (reasonably) uniform thickness, to mark & cut edge floor bricks. There was a noticeable unevenness between various bricks. This was obvious at the side, but present for bricks in the middle of the floor as well (with uniform brick thickness). I suppose I could mix a quick batch of v-crete only (no perlite) to smooth the top then let it cure again. Then proceed with cutting my edge bricks & 1st course angle cuts.

Wow, I may have just talked myself into a path forward while writing this reply.

[david s]

The usual method is to make a 50/50 mix of sand and clay about 1/2" thick as a leveller. The mix can be applied wet or dry. It is better if the mix is used dry IMO because it makes brick removal easier down the track if required and you want the floor bricks to be able to expand and contract freely, that's why they're best laid loose. It is also best to allow your vermicrete layer at least a week to dry out somewhat before building over it or you lock in the water which is more difficult to remove later.

[shanxk8]

My p/v-crete has cured for over a week already. I am thinking just to deal with the bumpiness that seems to prevent a flat floor to do a small layer of v-crete (without larger perlite particles) to smooth it out.

Part of the reason for thinking of this is that I haven't had luck finding fire clay (and just received my high heat mortar today). Don't want to keep searching just for leveling purposes.

The layer i would be adding would be varying from 0 to 5 mm if i had to guess.

[david s]

Just dry sand will work ok then

[shanxk8]

Thanks, that is easy