hearth done - brick floor and dome next

[boccu]

hi and happy new year to you all!

I have laid the hearth using approx 3.5" concrete (with reinforcing rebar somewhere in the middle of that) and approx a further 3.5" vermiculite / cement (6 : 1 by volume) mixture on top. All was well propped up and boxed in, so hopefully that's not going anywhere in a hurry!

Next step will be to lay my oven floor and start off on the dome. That should be the fun bit! Just a couple of quick questions to the more experienced of you out there:
1. er .....will the vermiculite layer eventually harden? This was laid 3 days ago and is still crumbly - I have stood on it so it is solid, but I can dig out holes with my finger if I wished.

2. I have not managed to find any fire clay or refractory cement where I live. Are these really necessary or can I do without either or both of them without risking the oven to cave in?

thanks for your help!
cheers

[james]

Re: hearth done - brick floor and dome next

Happy summer to all of you down south. We just got back from two weeks in the UK and didn't see the sun the whole time.

Your vermiculite concrete will stay pretty crumbly, but it is up to the task of holding your oven upright and level. It has really good compression strength.

It will be OK building your oven without refractory mortar, using the fireclay mortar recipe from the plans. But, I would be nervous about not adding the fireclay to the mixture. I would be concerned that a standard mason mortar would spall and eventually burn out/give up -- which would be bad. With all the effort you are going to put into your oven, it would be a shame for it to not last.

Can you keep looking for fireclay?
James

[boccu]

Re: hearth done - brick floor and dome next

thanks for that James. I'll keep looking for some fire clay, I'm sure I'll find something but may have to pay extra for freight ....... it is quite frustrating not finding exactly what you need on your doorstep sometimes isn't it??

Would you be able to tell me more or less how many kgs of fire clay I'd need for a 42" dome?

It seems like you're having quite a time keeping the spammers out of this forum. Some people just want to spoil it for everyone else - I just hope they don'e manage to ruin this forum coz I think you're doing a great job here!

cheers
john

[jahysea]

Re: hearth done - brick floor and dome next

Hi John. For reference I used 1 bag of fireclay. That was enough to put the brick floor down and to mix enough mortar for the entire dome. I used 1 part fireclay, 1 part lime, 1 part portland, 3 parts sand for the dome mortar. The material is quite light. I don't know the weight of the bag I used, but it was about the same size as an 80 pound bag of concrete.

[boccu]

Re: hearth done - brick floor and dome next

Thanks JC - I'll try to keep this as a benchmark ...... but I'm sure to need more than you as I'm sure to have larger gaps to fill in!!

cheers!
John