Medium vs Fine grade Vermiculite?

[GianniFocaccia]

Re: Medium vs Fine grade Vermiculite?

I do not know about freeze-thaw properties, but you do not need any block to augment the strength of the support slab. A 4" thick slab with rebar spanning your block stand is sufficient. It might be advisable to let your support slab concrete set up a little (next day) bit prior to pouring your vermicrete insulating slab. Vermicrete dries to a firm, but spongy texture that can be easily scraped away with a fingernail, but is plenty strong to support a floor firebrick lying on it's side.

[dmun]

Re: Medium vs Fine grade Vermiculite?

4x8x16 cement blocks under the cement base hearth for support. I do not feel too comfortable with the rebar supporting the weight of the entire oven and dome.

You are of course welcome to do anything to increase your comfort level, but you really don't need to worry about the support of the dome. First of all, it's over engineered to begin with, and second of all, most of the downward forces are on the periphery of the dome, the floor and insulation in the center are lighter weight by comparison.

There are lots and lots of ovens completed, and only a handful have center supports under the dome.

The vermiculite concrete hardens, but it's not rock hard. "Cork like consistency" in how it's usually described, meaning it can flake off at the edges. It has more than enough compressive strength to support your dome. Again, it's a technology that has been widely tested and supported. They make swimming pools out of the stuff, and man, water is heavy.

[thamnophis]

Re: Medium vs Fine grade Vermiculite?

I'm glad I found this thread. I've been waiting for days for my 5 inch vermiculite layer to dry rock hard. It is indeed a bit spongy or cork-like. I guess it is time to get back to work!

[Neil2]

Re: Medium vs Fine grade Vermiculite?

A 4 inch suspended slab with about 1% rebar by volume is plenty strong enough (0.5 % each way). Do some research or get advice on rebar placement. Do not have "loose ends". Rebar ends should have a hook or a 8 to12 inch right angle bend.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

A 4 inch suspended slab with about 1% rebar by volume is plenty strong enough (0.5 % each way). Do some research or get advice on rebar placement. Do not have "loose ends". Rebar ends should have a hook or a 8 to12 inch right angle bend.

I finally got the cement blocks mortared in place. I need to do the cement slab next. Standard readymix quickrete cement will do here I suppose?

Should the rebar grid be at 1 foot spacings? This is the first mention of hook in the rebar that I have come across. Should the hook go into the holes of the cement blocks? Not sure what is meant by loose ends??

After the cement block comes the verimculite. The formula is 5 parts vermi to 1 part portlamd cement , correct? No rebar in this step either?

Any advice from the oven masters is appreciated.

[dmun]

Re: Medium vs Fine grade Vermiculite?

Standard readymix quickrete cement will do here I suppose?

Two different things. Readymix is the stuff that comes in the big truck. Quickcrete concrete mix comes ready to add water in bags. Either will do fine: Needless to say having the readymix truck come in saves a lot of work.

If you are going to mix your own concrete, get help. It's a lot of work, and you want to work fast enough to pour the entire slab before the first batches set up. A mixer is a big help.

I didn't bend the end of my rebar. Stuff's hard to bend. No rebar in the insulation layer.

[leckig]

Re: Medium vs Fine grade Vermiculite?

you can rent a concrete mixer from Home Depot or Ace Hardware for less than $30. Do it!

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

Thanks for the responses. I poured the suspended cement oven base yesterday. Tomorrow I will do the vermiculite.

The mason I hired is trying to convince me not to use old red bricks as the oven walls/ceiling. I plan on firebricks for the base and to save $$$, I planned on old red brick as the walls/ceiling. The mason says it will not last one season and to go firebricks all the way. Any bad experiences with old red brick from others is appreciated.

[leckig]

Re: Medium vs Fine grade Vermiculite?

I dropped one of those red bricks on my foot once. Horrible experience it was!

Seriously: he is right.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

Are your oven dome and walls all firebrick?

[aeu99217]

Re: Medium vs Fine grade Vermiculite?

i've built mine out of old pressed reds as i didnt want to spend hundreds on firebricks which seem to be more expensive here in the uk. However, i did ask on this forum and there seems to be a school of thought emanating mainly from oz that old pressed reds can be used as they were fired at a higher temperature. Next week i'll be ready to start firing the oven so i'll post back in a couple of weeks and let you know how i got on.

[Tscarborough]

Re: Medium vs Fine grade Vermiculite?

How much did you save if you have to tear it down and start over again?

[aeu99217]

Re: Medium vs Fine grade Vermiculite?

it wont have cost me anything cause i got the bricks for free off gumtree.

They aren't any old engineering bricks though. They are old pressed reds which according to the aussies can cope with the demands of back garden pizza baking. Summers in Glasgow last for 4 weeks, if you're lucky, so it's not going to have to withstand industrial scale cooking.

[Tscarborough]

Re: Medium vs Fine grade Vermiculite?

Dry pressed solid commons as a rule are fine. They are also not very common and cost almost as much as firebrick in most parts of the United States. For example, I sell used solid commons for .80 each and firebrick for $1.40, so for an average oven you will save maybe a 150 bucks?

And that is if you can find the right kind of bricks, because 90% of what are available are not the right kind over here. Unless you can tell, and I assume his mason can, why take the risk?

[aeu99217]

Re: Medium vs Fine grade Vermiculite?

well let's hope mine are that type. I had someone from oz have a look at photos of them and he asked me to bash them up: he seemed to think they are ok. I got them from old tenement buildings which are about 100 years old (the bricks themselves probably arent that age as they are from internal walls) so i wonder if they are rare because they are mainly found in old buildings?

Certainly if the difference is that little then obviously firebricks are the way ahead but if old pressed reds are available for much less in the local area (in my case nothing) then the risk might be worth it.

Nonetheless, only time will tell as to whether the bricks are suited. Fingers crossed