Poured hearth, questions about concrete and insulation...

[Frances]

First the questions:

I read somewhere that if you add some washing-up liquid to the water in the cement, you can get away with using far less water for the same workable consistency because it reduces the surface tension of the water - does anyone know anything about this? I tried it on some smaller projects and you do need less water, but I didn't on the hearth as I was worried it might reduce the strength or something.

I've been looking for insulation and someone suggested using stonewool. Someone else gave me some (10 year old) glasswool that they used on their oven, though not enough for the entire insulation. I googled both products and was a bit worried by some of the results. One company wanted the equivalent of about 500 USD just for insulating slabs to put under the oven! However, I did locate vermiculite... I'll put the information in the vermiculite thread in a moment. The only thing is, my hearth is alread quite high - I'm worried I'll have to use a step ladder when I use it.

So, stonewool, 10-year-old glasswool, stepladder, keep looking, what do you think?

Anyway, here are the picks. I used my tried and true learning-by-doing-hope-no-one-ever-sees-this method of construction, and its still standing. Btw, the righthand corner is not in fact lower than the rest, it just looks that way because the frame walls are uneven...

[Frances]

So, after all the advice , I decided to go with the Vermiculite. I put it down two days ago, and now, like everybody else, I'm suddenly worried. In this case that the Vermiculite particles were too big... they're 4-8 mm and the consistency is more like chocolate coated popcorn than oatmeal. All the pictures I can find seem to show a different consistency. How big is the US Vermiculite then? Will I be ok with mine?

Sorry to whitter on, but you all know what Vermiculite is like. Hope someone can reassure me...
Frances

[asudavew]

What was your mix? 5 to 1?

And did you just wet it until you could squeeze just a bit of water out of it?

If so, from what I've read, it should firm up nicely in about a week.

It should eventually feel and act like cork.

But this is just what I have read.

[Frances]

Yeah, I think I got the mix right - actually I thought the stuff was quite fun to work with. It seems to be firming up ok, too.

The thing is, its going to be more like cork made from popcorn than cork made from oatmeal. As it were. I mean it was a really chunky mixture.

[asudavew]

I think you will be fine.

It's recommended to use the fine grains, but the coarse ones will work too.

[barbarian]

can a extra thick layer of fine grade vermiculite be used instead of the fire bricks to make the hearth ? anyone tried that yet or does it crumble and end up on the bottom of your pizza ??

[asudavew]

Originally Posted by barbarian

can a extra thick layer of fine grade vermiculite be used instead of the fire bricks to make the hearth ? anyone tried that yet or does it crumble and end up on the bottom of your pizza ??

Nah. The vermiculite is for insulation purposes. The bricks hold heat, provide thermal mass, and create a hard surface to cook your pizza on. You pour a concrete layer for strength, followed by a vermiculite layer for insulation, and then a layer of bricks for thermal mass and heat storage.

[barbarian]

Thanks .. duh I should have used my brain..
I have done 9 hours straight of reading I just stumbled on one thread discussing a similar question.... I am not kidding I just paused 30 min. for dinner
this is the date of my subscription to the forum LOL
Date: September 14, 2007 2:33:40 PM EDT
this is awesome and pathetic at the same time

Originally Posted by asudavew

Nah. The vermiculite is for insulation purposes. The bricks hold heat, provide thermal mass, and create a hard surface to cook your pizza on. You pour a concrete layer for strength, followed by a vermiculite layer for insulation, and then a layer of bricks for thermal mass and heat storage.

[asudavew]

Originally Posted by barbarian

Thanks .. duh I should have used my brain..
I have done 9 hours straight of reading I just stumbled on one thread discussing a similar question.... I am not kidding I just paused 30 min. for dinner
this is the date of my subscription to the forum LOL
Date: September 14, 2007 2:33:40 PM EDT
this is awesome and pathetic at the same time

Obsessed already?

I understand......... trust me!

[barbarian]

Originally Posted by asudavew

Obsessed already?

I understand......... trust me!

Yup I caught the bug