dome 'cap'??

[boccu]

Hi - I have read through many of the success stories on the forum and notice that the most challenging part of the construction is probably the final few rings of the dome. The bricks get harder and harder to shape and gravity always tries to win. This has resulted either in excellent looking oven roofs seemingly worked with precision cad cam instruments, or other more earthly looking - but hopefully similarly robust - roofs with mortar-filled gaps. I have come across a magazine article published earlier this year in NZ which makes the simple suggestion of making a plug out of refractory cement in place of the final rings of fire brick. This is moulded using a piece of plywood propped up on a box and then covered in sand to the level of the bricks and domed. The sand is covered with wet newspapers before the refractory cement is poured over it to form the plug. I also thought that keeping the odd bits and pieces of fire brick and crushing them to use in this final mkortar plug will probably also help.

To me this sounds far simpler than trying to shape those final bricks .... but will it work? Any thoughts on this from the more experienced masons out there?

John

[KiwiPete]

Hi John,

nice to see another Kiwi having a go!

Pouring a dome cap is really a piece of cake.

I used styrofoam vanes for support.

Have a look here http://www.fornobravo.com/forum/pomp...petesoven.html for more info. Page two shows the dome cap process in quite a bit of detail.

Good luck.

Peter

[boccu]

Hi Peter - good of you to make contact! Yes I have been through many of your postings - just to see what tools and materials you managed to find here in the land of the long white cloud! I had seen the plug that you made, and I thought it was a really good job. I think this only replaced the very last ring of bricks? It seems like the plug on the magazine article I mentioned (from The Shed) replaces about three or four rings, thereby doing away almost completely with the more difficult bricks and the need for styrofoam vanes. I'm not sure whether this would be structurally sound, that's all.

On another note could you please let me know where you got the insulation blanket that you used? What it it called ...and how costly is it?

cheers!
John

[james]

Making a plug

John,

You can make a plug, if you don't want to cut those last bricks. There are a few builders who have done it that way. I like your idea of using brick fragments within the refractory concrete. I would also make sure you make the plug from a real calcium aluminate refractory -- as that part of the oven will see lots of direct flame.

As a fun side note, check out the ancient Pompeii Ovens. They built their ovens that way. Here are the photos:

http://www.fornobravo.com/pompeii_ov...tos/dome2.html

Welcome aboard and enjoy your summer!
James

[CAM]

Refractory Concrete

Any suggestions on what type of refactory concrete. I would love to eliminate the cutting of the last bunch of brick. I'm guessing all brands are not created equal.

[KiwiPete]

Re: dome 'cap'??

Hi John,

With regards to the insulating material:

I used "Rockwool" from Forman Insulation in Penrose, Auckland.

You can find more info about it here: Forman Insulation

I got a roll of the stuff of about 3 metres which was about 3 inches or so thick. It came with a backing of wire mesh which was handy for "shaping" it and tying it down.

With regards to your other questions about the plug: yes I only did the final bricks. If you have a reasonable saw to cut bricks with, tapering bricks is not that hard, although it can be time consuming.

Re the styrofoam vanes: I do not think that I could have built my oven without them. I did make a fairly aggressive shape dome (low ceiling), so maybe you might be OK. I found they made life much, much easier.

[KiwiPete]

Re: dome 'cap'??

John,

re some of the other stuff:

I got perlite from here: Inpro

I bought new firebricks from a refractory place in Manukau called "Crow Refractory Ltd" ph: 09-278 2005.

They also sold me the refractory concrete and also have vermiculite.

Alternatively, you can go to Shinagawa Refractories Australasia NZ Ltd. They are in Huntly (ph 07-828 7019).

And yes, firebricks are bloody expensive here. That was one of the reasons why I decided to go with a thinner walled pizza oven and cut the bricks in three. (so ending up with about 3 inches of wall thickness). I tried to counterbalance the potential loss of thermal mass by going all out on the insulation.)

I know that it may not be a lot of use to you, because you're in Palmerston North, but there it is..

[boccu]

Re: dome 'cap'??

Thanks peter - some good leads there as I have not yet managed to find any refractory cement or fire clay here. I'll call the suppliers that you used and see what it will cost me to have it sent down to PN. Do you remember how much refractory cement you needed? 1 bag of 25kgs enough?

My base is now done and I'm just waiting for the damn rain to stop so that I can get on with setting the hearth and starting on the dome.

Enjoy your xmas!
John