#11  
Old 05-27-2014, 02:04 PM
Laborer
 
Join Date: May 2014
Location: France
Posts: 95
Default Re: Concrete Calculations

Hi folks,

So I've actually cast the first of 4 sections of my dome. Everything going well so far. I used iced water and had plenty of time to work with the mix. The batch I prepared left me a little short by 1 to 1.5 cm of thickness (I was shooting for 7cm). Is there any problem with adding another layer? If so, do I need to wait until the previous layer has set? I presume I would need to use the same mix?
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #12  
Old 05-27-2014, 02:37 PM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,691
Default Re: Concrete Calculations

You can add on another layer straight away, but it won't be as good as if if it were cast in one go. The other alternative is to leave the casting as it is and thicken it up when the oven castings are all assembled.
Reply With Quote
  #13  
Old 05-27-2014, 03:10 PM
Laborer
 
Join Date: May 2014
Location: France
Posts: 95
Default Re: Concrete Calculations

Quote:
Originally Posted by david s View Post
You can add on another layer straight away, but it won't be as good as if if it were cast in one go. The other alternative is to leave the casting as it is and thicken it up when the oven castings are all assembled.
Thanks David. When you say thicken it up one assembled, won't I risk cracking if I cover over the assembled sections?
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #14  
Old 05-29-2014, 10:30 AM
Laborer
 
Join Date: May 2014
Location: France
Posts: 95
Default Re: Concrete Calculations

Ok, so I've cast my dome... using a ciment fondu/grog/sand mix. Just waiting for the last section to cure.

What's the deal with curing fires? Do they just speed things up, or do they lead to better strength/performance?
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #15  
Old 05-29-2014, 02:18 PM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,691
Default Re: Concrete Calculations

By casting your dome in sections you are telling it where you want the expansion stresses to occur. If you cover over the dome with another layer any expansion cracking will take place where you have designed it, rather like grooves in a concrete slab.

Re driving out the water, firstly, did you add any burn out fibres to your home made castable? If not then you will need to proceed extremely slowly. Recommended firing schedules for commercial castles (that do include burn out fibres) are in the range of 25 to 50 C /hr Particularly for the 100- 300 C range where steam explosions are most likely to occur. The temperature of the castable will vary wildly between the top of the dome and the base as the base is way wetter and cooler. You can't take it too slowly, but you certainly can take it too fast. If you are having fine weather then leave it exposed to the sun and wind for a couple of weeks to do much of the drying for you. It's a bit like trying to fire a clay pot that hasn't dried. It can be done, but is way more risky.

The firing will not add extra strength to your castable unless you fire it to around 1000 C. Do not attempt to do this as rapid chemical changes take place around 550 C that can damage the refractory and firing with wood is impossible to control in a slow enough temperature rise to do this safely at this range.Your mix should perform ok, but will never be truly sintered.

Last edited by david s; 05-29-2014 at 02:42 PM.
Reply With Quote
  #16  
Old 05-29-2014, 03:19 PM
Laborer
 
Join Date: May 2014
Location: France
Posts: 95
Default Re: Concrete Calculations

Thanks David, really appreciate the advice.

I did add burn-out fibers. I cut up some polypropylene rope. Not much though, and I didn't separate the fibers very much. Nice weather here in the South of France... I might just let it dry naturally for a good while before firing up. Since mine is in sections, I could, for example, turn them upside down in the sun to dry the inside.

Here is the advice from the Ciment Fondu website:


It is advised that the first firing does not take place
before 48 hours after casting. Then to carry out a
gradual rise of 50C/hour and holding for at least 3
hours at 110C before then continuing up to 500C.

What do people generally use to control the temperature of initial firings?
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #17  
Old 05-29-2014, 06:34 PM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,691
Default Re: Concrete Calculations

Using an alternative fuel is a very good method, but we're not allowed to discuss it on the forum. You may be able to find some good solutions on the curing thread or PM me.

Last edited by david s; 05-30-2014 at 04:40 AM.
Reply With Quote
  #18  
Old 05-30-2014, 04:21 AM
Laborer
 
Join Date: May 2014
Location: France
Posts: 95
Default Re: Concrete Calculations

Thanks again Dave.

I'm wondering, since my oven is cast in sections - would it make sense to do some curing before I mortar them together? There'd be a lot more surface area for moisture to escape.

In this case, are there any special precautions I should take? Otherwise, I could just follow the standard instructions with my un-mortared dome and then some again once I've mortared. Would that make sense?
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Concrete Counters UtahBeehiver Pompeii Oven Construction 27 03-21-2014 09:55 AM
Alternatives to concrete hearth kebwi Pompeii Oven Construction 9 09-02-2009 08:58 PM
Concrete for the hearth slab. I burnt my fingers Getting Started 6 08-23-2009 08:46 AM
Alternative to concrete block foundation ekah Getting Started 6 12-02-2008 06:56 AM
Curing Concrete and Masonry Xabia Jim Tools, Tips and Techniques 21 03-31-2008 02:15 PM


All times are GMT -7. The time now is 03:40 PM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC