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Oven Floor Not as Hot as it Used to Get

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  • Oven Floor Not as Hot as it Used to Get

    I'm a long time owner of my Forno Bravo Casa90 as you can see one of my original pizza photos here in an old post from 2006:

    I've had this wet oven problem since I've assembled the oven back almost 10 years ago with moisture getting in the oven. After trying all sorts of sealants on the outside nothing seems to work except fully covering the oven with a tarp and even then it gets wet somehow?!? I posted about it here in 2006:

    After years of just dealing with it - by drying out the oven for a few days prior to use via a space heater I now have an oven where the floor of the oven doesn't seem to be as hot as it used to get. I have a temperature gun and although it shows a range of 800 down to 600 from the coals moving towards the edge (after I push the coals away) I remember years ago the floor would be even hotter. The problem is that I can tell with the pizza. The top of the pizza cooks in 2-3 minutes to a nice burn but the pizza is never cooked from the bottom and I no longer get those nice black spots on the bottom as you would expect. When I say never cooked from the bottom it cooks somewhat but as a pizza maker you can easily tell that the pizza is pretty much ONLY cooked from the top.

    In talking with others I have decided to try and dry out the oven fully this weekend. Today I had the oven white with a constant fire for probably 10 hours (after keeping it dry and some smaller fires for a few weeks) and then at the end cooked some pizza. Unfortunately it had the same results. The one thing I did notice (since I was looking around) is that under the cooking surface where it's the bottom of the concrete I assembled years ago (i.e., at the top the location where the wood is stored) it was hot - very hot where I couldn't keep my hand touching it. To me that tells me that heat is escaping from the bottom. Now I don't remember exactly the instructions on assembly from back then but it was mixing cement with vermiculite and I probably have the recommended number of inches under the oven floor - I found this set:

    So my questions are:
    1) should the underneath be so hot?
    2) if not then what can I do without ripping the oven apart and redoing the base? Can I buy some sort of insulation to put under the oven floor (i.e., top of the wood storage?)
    3) if it does get that hot then why is my oven floor not getting as hot as I'd like? Do I need to dry it out more? How long?

    Thank you in advance for reading and helping me.


  • #2
    Re: Oven Floor Not as Hot as it Used to Get

    As you have been following the manufacturers plans and instructions then your question should really be referred to them. I believe that the most likely cause of your problem is that you probably still have water in your vermicrete layer and that is causing its inability to insulate properly. I did conduct an experiment (attached) on the drying of a vermicrete slab that demonstrates the importance of drying it out before building over it. There is a large amount of free water that is not used up in the hydration process when the vermicrete hardens. This has to be removed. If this is the problem the remedy is to continue to fire the oven until all the water has been purged.It is too late now to replace the insulation between the floor and the supporting slab. As your oven is 10 years old it sounds like water is re-entering after you've dried it. Perhaps water is wicking up through the stand. Check to make sure no sprinklers are watering it regularly.
    Attached Files
    Last edited by david s; 08-09-2014, 06:42 PM.
    Kindled with zeal and fired with passion.


    • #3
      Re: Oven Floor Not as Hot as it Used to Get

      It sounds like you have diagnosed your problem, as it seems like the heat is escaping through the floor. Additional insulation would keep the heat in.

      I am no expert, I lurk a lot and plan to start an oven, but I only can offer my uneducated guess.


      • #4
        Re: Oven Floor Not as Hot as it Used to Get

        David S, I believe I dried it out initially since my oven was working properly for years. I do believe (well I know) that somehow water has been getting into the oven most likely from below (coming up from the slab) or from the entry where my landing is not leveled correctly and the water is just coming in. In either case I'm sure I still have water in the vermiculite portion and I will continue to try and dry it out with fires.

        In addition I was reading lots yesterday on the forum and I've been thinking about either:

        1) drilling holes in the bottom to let it drain - although I can't see this really working or
        2) adding more insulation underneath - I've read about SuperIsol (Cal-Sil) but have no experience with that or even knowing where to buy some....and not sure if that's my solution either.


        • #5
          Re: Oven Floor Not as Hot as it Used to Get

          Since the problem has developed over time there is usually a reason and like a car that doesn't run well and you find one problem you just keep looking cause there is usually 3!
          Cracks in the dome render, particularly at the base. Even if they are only hairline they will wick water in. Possibly chase them larger and squeeze in some paintable silastic and a full coat flexible paint designed for the purpose.
          Cracks around the steel chimney and render due to uneven expantion. Chase out and high temp sealer possibly an automotive product .
          The hearth floor and entrance floor. If any rain falls on this its a short pathway to the hearth insulation. I've made an external weather door to prevent this, and have found it this to be my major problem area.
          In saying all this I have long ago excepted that from time to time my oven will not be perfectly dry even the inside surfaces will draw moisture from the air. A few low heat fires will bring things back to balance. And any fire I usually find something to cook anyway
          Hope something helps
          Regards dave
          Measure twice
          Cut once
          Fit in position with largest hammer

          My Build

          My Door


          • #6
            Re: Oven Floor Not as Hot as it Used to Get

            Ok this information may be useful for others who are in the same situation.

            By lighting fires for 2 whole days (I did it one week apart) that seemed to do the trick.

            After doing that I was able to get a nice burn on the bottom of the pizza (see image - although the following week it was even nicer).

            The time after that I was able to get the floor of the oven even hotter. i.e.,
            assuming I had the wood on the right, the middle of the oven floor was 850 - 975 degrees and the left side was 750-850. This temp worked very well for my pizza which I was able to cook between 90 seconds and 2.5 minutes.

            I still have an issue of a wet oven which I believe is mostly likely due to two main issues:
            1) water coming up from the footings. I don't know how to stop this. Maybe drill holes in the way bottom of the oven stand??
            2) water coming in from the entry point of the oven. I now cover the whole front part of the oven so no water can come in.

            Also I make sure I use lots of wood to heat up the oven and fully wait for the entire inside dome (and I mean entire) gets white.