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cut into the hillside - Forno Bravo Forum: The Wood-Fired Oven Community


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cut into the hillside

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  • cut into the hillside

    What I hope to do is like building a basement house cut into the hillside. When I stand in my back yard the garden rises to about 5 foot so I have cut out a level into the clay and laid the concrete base, ran drains around but the water soaked up through and kept my oven floor wet. I just had to take my first oven apart due to constant rising damp.

    Ready to start again, so need advice how to build an oven directly on to the clay ground.
    Should I just lay some plastic sheet under the insulation, and then up the back of a retaining wall to keep the hillside soil separated from the dome outer skin, when built.
    I would prefer not to leave a gap of a few inches but somehow allow the soil to fall directly against the back of the oven dome.
    So it will need protection from damp rising and water penetration.

  • #2
    Re: cut into the hillside


    If I am understanding corrrectly, it would seem to me that all you would need is a water proof membrane between the insulation of the WFO and the soil. Since you would be on the cool side of the insulation something like EPDM would work.

    EPDM is the same material modern tire innertubes are made of and is available in quite large sheets as it is commonly used for pond liners. They don't give it away but often those building ponds have "drop" which can perhaps be gotten cheaply (or at least at a significant discount from retail). Likewise another source is drop from roofing projects, although roofs being usually rectangular are less prone to having drop as opposed to ponds which are rounded making for corners which are usually cut away.

    I would recommend it over polyethylene (polythene) sheeting which breaks down even when buried.

    It's quite flexible and absolutely waterproof and although larger sheets weigh alot, is fairly easy to work with (a 40ft x40ft sheet of 45 mil weighs almost 500lbs). Thinner thicknesses are available.

    Hope this helps,


    • #3
      Re: cut into the hillside

      Yes, or even lay it on the finished dome before backfilling. That would work too if it didn't also trap rainwater that ingresses, wicking water to the base. Is that why you suggested putting it inside the outer course? Aha! Clever. Thank you so much Wiley.

      What did you use for the outer skin? From reading the site it seems a 3course stucco but how does that give a waterproof outer surface? Perhaps by using ceramic and vitreous mozaic as I have seen on some Italian jobs.


      • #4
        Re: cut into the hillside

        there are two issues to solve, the base sits on clay, and the hillside leans against the backside of the dome.

        So I should use a membrane under the floor but not over the dome.... inside it.

        EPDM under the floor insulation, but on top of the slab is that correct?

        EPDM up the back, over the insulating blanket but under the wire and first render. Is that correct, prevents capilliary wetting of the outer face which could happen if I were to wrap the dome in waterproof membrane.


        • #5
          Re: cut into the hillside


          On my WFO I simply ended up painting the outer stucco with an acrylic paint. That lasted quite well for three years and recently I repainted using 3 coats of elastomeric acrylic (a product called "Kool Seal" which is white in color) as it came from the can followed by a fourth which I tinted with the same acrylic paint I used previously and then a final coat of that same acrylic paint. The reason I tried the elastomeric was because I was starting to see some fine hairline cracks where the dome transitioned to the base. To soon to tell if the recent multi-layer/coating will be worth the effort and time expended but looks fine. Although the effort and time were minimal taking less than 30 minutes to paint and clean up afterward for each coat.

          If the dome is well insulated such that the outer surfaces stay ambient temperature I think one can probably use any good exterior paint that is compatible with stucco.

          As for where one would place the previously suggested EPDM layer: I would build the entire dome all the way to stucco exterior surface and then have the EPDM lay against it followed by the backfill. I would suggest if you go that route that you simply excavate the hillside; place the EPDM (folded corners at the back of the hilside excavation with the vertical portion temporarily held upright with light bracing); build the base and WFO then lay the vertical portion of EPDM against the dome and backfill. The stuff is the same material as innertube; it is strong, stretchy without being too elastic and conforms quite well to irregular surfaces. Covering a dome might create a few wrinkles but I think would pose no insurmountable problems. Don't cut the EPDM when making the back corners rather fold them like one would a bedsheet...the stuff doesn't pinhole at corners. It can be glued and they make tape for seams but that is much more hassle than simply folding.

          Hope this helps,


          • #6
            Re: cut into the hillside

            In addition to Wiley's suggestions, I would attempt to place a 4 inch granular drainage layer both under the slab and if possible between the fill and the dome.


            • #7
              Re: cut into the hillside

              Today, 12:10 PM
              Il Pizzaiolo

              Join Date: Apr 2007
              Location: Adelaide, South Australia
              Posts: 1,606

              My oven is built into an earth wall and it sits upon the reinforced concrete and brick retaining wall.
              When I dug the foundation slab into the heavy clay base, I laid some builders plastic (called Fortecon), beneath the slab which stops any moisture from rising through the slab. However, the falling rain simply ran down to the foundation and entered the oven through my soldier course and caused me to have to dry the oven out before heating to pizza temperatures. I overcame this problem by digging a "moat" around the foundation, ensuring that it was at least 150mm lower than the cooking surface, lining it with plastic, laying a perforated agricultural pipe in the trench and burying it with river pebbles.Any moisture and water now runs into the trench, through the pipe and down the drain. I also covered the oven with a polycarbonate roof to keep it dry from the rain and the water that flowed off the patio roof.
              I now have no water problems at all allowing the oven to reach 500˚C in just over an hours firing.




              • #8
                Re: cut into the hillside

                Thanks Neill, I reposted your note here for the thread.

                When I say I removed my first oven, (it was a barrel oven anyhow, it never reached high enough temps, stopped rising at about 450deg after an hour nomatter how many more logs I burned)
                I still have the concrete slab remaining, Wiley. hope it will do to run the epdm over it. As for the 6" trench, I did run stones and agricultural pipe around the back, but not that low, and the slab sits on clay not granular drainage, so the water is obviously not getting away. By granular drainage I presume you mean gravel about 15mm?