Go Back   Forno Bravo Forum: The Wood-Fired Oven Community > Good Background Information > Forum Guidelines

Like Tree1Likes

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 12-07-2010, 07:48 PM
Serf
 
Join Date: Dec 2010
Location: usa
Posts: 10
Default Pouring the hearth

If one plans on having a hearth made up of a concrete slab and an insulated slab on top of it do you wait until the concrete dries/cures before poring the insulated slab and, if so, how long do you wait before pouring?
Also, is the surface of the insulated slab diferent in appearance and texture from the conrete slab? That is, will it have the same finished look?
Lastly, if you want to add color to the slab will the two different types of concrete end up looking the same?

Thanks
bobnnorm@ptd.net
Reply With Quote
  #2  
Old 12-13-2010, 09:59 PM
Serf
 
Join Date: Nov 2010
Location: Denver Colorado
Posts: 5
Smile Re: Pouring the hearth

Hey I am new to this and will build this summer; but I am in construction and if you leave the hearth slab a little rough then when you pour the insulating slab it will have "tooth" to attach to the lower one and then finish the insulated slab with a hard trowel finish ( flat). As for color if you add the same amount of color to each slab they should be close to the same color the insulating materials might cause some color variation, that I am not sure about. And you should not have to wait until the lower slab cures before installing the insulation slab on top. There maybe other threads out there that are more correct than what I have said, I am coming from general construction experience.
Reply With Quote
  #3  
Old 12-13-2010, 10:43 PM
Il Pizzaiolo
 
Join Date: Jan 2007
Location: Tampa, FL
Posts: 1,446
Default Re: Pouring the hearth

You do not have to wait between pours. In fact, the original Pompeii oven plans actually directed you to pour the perlite concrete or vermiculite concrete immediately after the support slab. The thinking was to get the best possible bond. It has been proven to not be necessary. NEITHER slab is going anywhere once poured and the oven built. So, if you want to or need to take a break between pours there will be no problems.

Insulating concrete (perlcrete/vermicrete) will both have a consistancy of oatmeal. YES, it will look funny and be a bit crumbly when dry, this is totally normal. Everyone seems to come on the forum directly after the pour, concerned something is not right. Do not be alarmed and give it a week to dry before proceeding with your floor and dome. A 5-1 ratio of perlite OR vermiculite and portland cement.

As for color, WHY? the insulating layer CANNOT be left exposed and must have some type of finish applied if extended beyond the footprint of the oven. The area under the oven is just that...under the oven so it won't be seen. The same applies if you are using it for your dome insulation, it must be finished. Even when used in a concrete mix, both perlite and vermiculite can absorb a tremendous amount of water (that is why it is used as a soil additive and conditioner by gardeners and horticulturists). Each grain can absord 10 times its weight in water. Speaking from experience, you do not want to have a saturated insulating layer at anytime after your oven is built.

RT
Reply With Quote
  #4  
Old 12-14-2010, 09:08 AM
Neil2's Avatar
Il Pizzaiolo
 
Join Date: Oct 2006
Location: Vancouver Island
Posts: 1,374
Default Re: Pouring the hearth

RT is correct. I, personally, would do the insulation pour the following day. The form work is going to be different anyway. The insulating layer will be smaller and "inside" the suspended slab.

Try to limit the insulating layer to between the suspended slab and the the oven. It should only be to the footprint of the brickwork and the corresponding insulating layer over the dome. Do not extend it to the edge of the suspended slab.
Reply With Quote
  #5  
Old 12-14-2010, 07:33 PM
dmun's Avatar
Moderator
 
Join Date: Jul 2005
Location: New Jersey USA
Posts: 4,216
Default Re: Pouring the hearth

Quote:
finish the insulated slab with a hard trowel finish ( flat).
I think you will find it is hard to get any kind of finish on the vermiculite concrete. About the best you will be able to do is pat it flatish. That's why a leveling medium is called for, between the insulating slab and the brick floor.
__________________
My geodesic oven project:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
,
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #6  
Old 05-12-2011, 04:53 AM
Leao's Avatar
Peasant
 
Join Date: May 2011
Location: nomad
Posts: 30
Default Re: Pouring the hearth

Quote:
Originally Posted by RTflorida View Post
Do not be alarmed and give it (the vermiculite or perlite mix) a week to dry before proceeding with your floor and dome.
Hi, is a week really necessary before you can proceed with the next step?

Quote:
I think you will find it is hard to get any kind of finish on the vermiculite concrete. About the best you will be able to do is pat it flatish.
If it is difficult to get the Perlite or Vermiculite concrete flat, surely the oven floor bricks that are laid on top of it will be really uneven?

Thanks again for your help,

LEAO +
__________________
Black Ink Drawings by Leo the Great -
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


Affordable & Imaginative Graphic Design by me & Claire -
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #7  
Old 05-12-2011, 03:16 PM
Journeyman
 
Join Date: Aug 2010
Location: Glendale, Arizona
Posts: 394
Default Re: Pouring the hearth

Hi Bobnnorm,

Here are my comments, I hope they help.

You don't actually "pour" vermiculite or perlite concrete. You shovel it in or dump from a bucket. Please don't tamp it down hard, just enough to fill the corners of the form. You don't want to compact it, it is insulation and relies on air voids. Use an angle iron or 2 x 4 to screed the surface of the vermiculite/perlite concrete. It should be level but you cannot smooth it. Place FB insulation board or other board over the concrete insulation if you want a smooth surface OR use a clay/sand mix to level the hearth bricks. I used 1/2" ceramic insulation board under my last oven to provide a smooth surface for the hearth bricks.

The concrete slab doesn't need a trowel finish except where it will be visible. It is advisable to use an "edging tool" to round the edges of the slab though. Go around once when the concrete is still wet to push the bigger stones down, then again when the concrete begins to set-up a little firmer. No need to get too precise about this since most of it will never be seen. I wish I could remember the forum member that recommended this. Maybe he will read this and offer additional helpful comments.

The vermicrete insulation should be firm enough after a couple of days. If you make your wooden forms using screws then you can leave them in place while you do the hearth work then unscrew the forms several days later.

The vermicrete layer stays very wet. It will set up rather slowly compared to a concrete slab and it will be crumbly if you bump it or rub a brick against it.

Cheers,
__________________
Bob


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



To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #8  
Old 05-21-2011, 03:01 AM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,518
Default Re: Pouring the hearth

Moisture underneath the floor in the perlcrete or vermicrete layer is the most difficult to remove later on, so if you have the time wait a few weeks for it to dry before covering with the floor bricks, which are going to have a tendency to lock the moisture in. I'm assuming fine weather here, you don't want any extra rain on top of it. The amount of water in the vermicrete layer is approx. double that which you would use in a standard concrete mix, so there is a lot to remove, why not let nature do the job for you if you have time.
Apologies if this advice is contrary to the Pompeii plans, just my advice from experience.
Reply With Quote
  #9  
Old 07-15-2011, 09:54 AM
mrchipster's Avatar
Il Pizzaiolo
 
Join Date: Apr 2010
Location: Minneapolis, MN USA
Posts: 1,214
Default Re: Pouring the hearth

Quote:
Originally Posted by david s View Post
Moisture underneath the floor in the perlcrete or vermicrete layer is the most difficult to remove later on, so if you have the time wait a few weeks for it to dry before covering with the floor bricks, which are going to have a tendency to lock the moisture in. I'm assuming fine weather here, you don't want any extra rain on top of it. The amount of water in the vermicrete layer is approx. double that which you would use in a standard concrete mix, so there is a lot to remove, why not let nature do the job for you if you have time.
Apologies if this advice is contrary to the Pompeii plans, just my advice from experience.
I would like to add one additional thought to this topic. the Vermiculite - Portland cement mix is a type of concrete ant thus should be cured damp. I highly recommend a plastic tarp or drop cloth to keep it from drying out to rapidly during the first 5 days or so - this will allow it to cure properly.

Just my two cents.
Chip
Reply With Quote
  #10  
Old 07-15-2011, 01:03 PM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,518
Default Re: Pouring the hearth

True , but as it's not really structural it's less of an issue. Additionally the extra water in the vermiculite should be sufficient to allow full hydration for that first week as the thing dries slowly, but covering would not hurt.
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
Advice on pouring the hearth Matt916 Getting Started 24 10-14-2012 05:57 AM
Pouring the hearth C5dad Newbie Forum 3 12-23-2010 09:01 PM
Pouring the hearth barnesy Getting Started 7 12-16-2009 04:55 PM
Pouring hearth Marc Olson Modular Refractory Oven Installation 12 03-09-2008 09:22 AM
Pouring Hearth Question telehort Getting Started 7 01-29-2007 09:20 AM


All times are GMT -7. The time now is 03:07 AM.

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