Re-starting from scratch

[Miguel]

Hi everybody,

Time to re-start an old project.

http://www.fornobravo.com/forum/f43/clay-oven-6303.html

It is a year now that I started my oven, but unfortunately I arrived too late to this forum and found myself with a total lack of insulation on the floor.
The end result is that the oven is unusable. No heat retention to talk about.

It is now time to gather momentum and restart.
Needless to say your help will be much needed. First problem: Due to the fact that the house is partially excavated in a mountain, the support slab is lying directly on the ground, and can get moist by capillarity. I would feel better if I could place a water barrier between the mortar hearth slab (already installed directly on the terrain) and the 4" 5:1 vermiculite mortar that will come next, to stop water to get into the insulation slab.

Do you think this is doable?

Any recommendation as to what material to use?

Do I need to get rid of mortar slab already in place) ?(please answer no to that one if at all possible.)

Thanks in advance

Miguel

[texassourdough]

Re: Re-starting from scratch

I would think you could use the slab... But creating a water barrier sounds like a good idea. The insulation you choose may help depending on what you use but a solid sheet of aluminum (or something like that) might be preferable. Then block insulation (or vermiculite as you suggest) and your hearth mass and floor. I think it should work fine!

You will probably end up raising the hearth of the oven a bit but that may not be a problem if it is not too high already. (Might even be beneficial).

Good Luck!
Jay

[Miguel]

Re: Re-starting from scratch

Hi jay,

The additional 4" rise is welcome, and this is one of the reasons why I am thinking on using vermiculite, instead of thinner materials.

In relation with the water barrier, thick aluminum foil seems a very good idea, but maybe not that easy to find in the neighborhood. Do you think that a sturdy plastic film will be up to the task?, I really do not know what is the temperature that can be expected under the insulation floor.

I do not even know if the vermicrete 5:1 is very water absorbent or not, but I failed the first attempt and I prefer to err on the other side, just for a change.

All the best
Miguel

[nissanneill]

Re: Re-starting from scratch

Hi Miguel,
it would be much easier to comment if we had a picture or two.
From your description, the oven is sitting on a concrete footing and the firebricks are on top of that?
The water from the surrounding ground is rising into your heath bricks through capillary action.
Well, there are solutions to all your problems, but you will need to get some gear and do it right next time.
My oven foundation is excavated into the ground behind a retaining wall but insulated with vermicrete and sitting in builders plastic.
I have since dug a reasonable trench around the rear of the oven through the clay, placed some plastic lining over the base and up the side of the oven footings, laid in some agricultural drain (slotted to capture any free water), covered with rounded river pebbles and then stacked dry retaining wall blocks or similar. That has solved the water problem easily.
To get your oven floor insulated, well I would excavate a couple of trenches beneath your oven approx 1/4 and 3/4 the diameter of the base. I would then slide some steel I beams through to the other side, dig out under the ends of the beams, put in a cement pad and locate a hydraulic jack under each end. Then I would carefully raise each jack slowly to give me sufficient room to insert a couple of sheets of insulation board over some plastic membrane. Getting the I beams out after lowering will be the challenge though. You might lower them onto the insulation board and carefully jemmy bar each side little by little, slide out the beam and slowly lower the hearth until it sits on top of the insulating board. Using a piece of steel plate between the jemmy bar and concrete hearth will help distribute the load over a larger area which would be easier to slide out once down completely.
A lot of work but unfortunately a small price to pay for that initial lack of knowledge but it will convert your oven to a good usable item.

Cheers.

Neill

[Neil2]

Re: Re-starting from scratch

As Neill notes, good drainage is important. With that, I would think that you don't need anything special on top of your slab below the proposed vermicrete layer.

I would make sure the existing slab has some slope and there is no ponding. You may have to grind a bit from the edge in to ensure this.

[lwood]

Re: Re-starting from scratch

There are many waterproofing materials that you can apply to concrete to stop any water from coming in. I would use something like a concrete based waterproofer and add your insulation on top of that.

[Raffy]

Re: Re-starting from scratch

I'm with John (lwood) on this one. I've done some research for my oven on waterproofing. My oven is an igloo style oven located outdoors and will be exposed to tropical storms and heavy rains which are common in my country. I didn't want an enclosed or gabled house oven because I like the look of an igloo, so, I went about researching waterproofing methods for the dome and hearth.

Here is a link to the thread on waterproofing: Waterproofing


Here are other links on waterproofing you might find useful:

Capillary Waterproofing

Other Waterproofing Options

Hope these help. I will be going with the capillary waterproofing. In addition, I strongly agree with Neil2 and Nissanneill about the drainage. Making a canal/trench leading away from the slab is important to keeping your oven dry.

Good luck


Raffy

[texassourdough]

Re: Re-starting from scratch

Hi Miguel!

I would not recommend plastic - it is too suspect to melting which could be a mess in MANY ways! (including fumes).
Jay

[Miguel]

Re: Re-starting from scratch

Thanks for all the input,

There is photo on this thread, I will try to find more and post them;

http://www.fornobravo.com/forum/f3/h...html#post52241

The oven construction on the photo will be inevitably destroyed.

As you (do not) see, the hearth concrete slab is sitting directly on the ground, and can become moist, absorbing water from the terrain.

If I understand right, I can; keep the slab as it is, then grind drainage channels on top of it, put a thick aluminum (no plastic) foil, pour the layer 4" of vermicrete 5:1, and continue from there with a nice, insulated and hopefully dry base.

Will keep you posted, but this is oven is sitting far from where I normally live, and will take some time.

Cheers,

Miguel