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Seattle 36" Pompeii

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  • Seattle 36" Pompeii

    I finally decided to pull the trigger and build my oven. After months of lurking on this board, absorbing all the knowledge I could, I began with my excavation three weeks ago and have made great progress in the time since. I plan to use this thread to share my progress and anything I might learn to help future builders.

    I live near Seattle and this spring has been pretty wet, but I've lucked out and dodged the rain every weekend since I started. That said, it hasn't been all that easy so far. I live on the side of a tall hill (read: ancient mountain) and that meant digging through hard clay that's full of large rock. Most of the rocks I excavated varied from the size of a small potato all the way to the size of a watermelon. By the time I was done excavating my build site, I came away with enough large rock to edge most of my front yard landscaping.

    Because I knew all the rock was there (although I didn't realize it would be this much), I didn't dare rent a tiller for fear of the damage the rocks would cause. I was limited to using the hand tiller I bought for my garden. It did a decent job of breaking up the dirt but the constant "clink" of a new-found rock turned it into a long and painful ordeal. It took the better part of three days to excavate enough dirt to place my forms and bring in the gravel, but the forms went in easy and I was fortunate to get it square with very little work.

    Attached photos:
    1. This bucket is a good representation of the rocks I found starting about 3 inches under the surface. I ended up filling two of this size of container with rock.
    2. An assortment of some of the larger rocks I found. It's no wonder I couldn't grow anything in my back yard with all these large rocks just below the surface.
    3. The forms are in with roughly 3 inches of gravel for drainage under the slab.

  • #2
    Re: Seattle 36" Pompeii

    The weekend after placing the forms and gravel, I bought my concrete and rented a mixer from Home Depot. I opted for 60 lb bags of concrete rather than the standard 80 lb bag. My reasoning is I would rather spend a little more and take more trips with less weight than risk injuring myself with the larger bags that I wasn't sure I could handle. It meant buying and using more bags, but I believe the decision was a good one since I came away with no injuries and only a minimal amount of soreness the next day.

    I used 38 bags of concrete, which meant about 15 "pours" from the mixer, but renting the mixer for the day was a great investment. My neighbor tried to convince me to mix it by hand in my wheelbarrow, but I can't imagine how much more time and unnecessary pain that would have caused. A full-day rental of a concrete mixer was only $42 and it was worth every penny for the time and effort saved. (Retail price for the mixer itself was around $350.)

    After I finished my pour and made a rough screed on the concrete, I decided to trowel it to give it a more smooth look. I had never done this before and I believe I wouldn't do it again if I were to pour another foundation. I wasn't very good at it and the end result was not nearly smooth or level enough. If you have experience troweling concrete smooth, I suppose it would be a good thing to do, but I mildly regret the wasted expense of the trowel and what little benefit it added.

    Attached photos:
    1. Laid down strips of 1' wide sheathing. The 10' wide sheathing was only a few dollars more and I wish I would have used that instead. When I made my first pours, some of my sheathing lifted up and folded, exposing the wet concrete to the gravel below and embedding the plastic in the concrete rather than under it. I can only hope this didn't compromise the long-term strength of my pad too much.
    2. My load of 38 bags of concrete, carried to my back yard 3-at-a-time from the curb in my wheelbarrow.
    3. Pouring a batch of concrete from the mixer. I may have been overdoing it with the chemical splash goggles, respirator and sleeve-length rubber gloves, but safety first!
    4. Troweling the wet concrete. I was told by a friend that I might have had better success if I had let the concrete rest for about 1/2 hour before starting to trowel. If I choose to do it again in the future, I will follow this advice.
    5. My concrete bag pile. Hopefully the garbage man won't complain too much with the trash can packed tight with the remnants from this pile...


    • #3
      Re: Seattle 36" Pompeii

      Well done on the start, looking forward to watching the progress! Don't worry too much about your concrete, as long it's strong (which premix should be) there will be no dramas!
      You probably won't see too much of the surface anyway!

      Boom Shanker! (Neil - The Young Ones)


      • #4
        Re: Seattle 36" Pompeii

        Did you leave any space between the forms and reinforcing bars? I think you're supposed to leave at least 2,5 cm gap from any surface of the slab to the reinforcing bars, otherwise it'll start rust.


        • #5
          Re: Seattle 36" Pompeii

          @Oz - Thanks. I agree about not seeing it and that's why I think it was probably a waste of effort. If there's ever a next time, I'll screed it and then leave it alone. I bought "extra strength" premix, so I would hope it will last for decades!

          @Laku - I followed the downloaded plans that called for the rebar grid to fit just inside the edge of the forms, so there was only a fraction of an inch gap (certainly less than 1 cm) at each edge. It might rust, but it shouldn't be seen since the foundation sides will be covered by the stone pavers I intend to put down after the project is complete.


          • #6
            Re: Seattle 36" Pompeii

            This weekend I built my stand. Saturday, I assembled the stand (which took way longer than I expected). To get it square, it took a few tries of assembling the first two rows and taking them back apart. After all the effort it took to just get it square, I didn't want to risk mortaring the first row to the foundation for fear I would undo all the work to get it squared up. The stand leans slightly to one side, so I'm hesitant to say avoiding the mortar was a good idea, but at least it saved my back (and my sanity).

            Following the suggestion from the Pompeii oven plans, I used angle iron to support the bricks over my opening. I spent the better part of the afternoon and evening grinding away parts of the bottom and faces of the bricks to allow it to sit level in the support beams. Don't be fooled by the documentation in the plans - this is neither quick nor easy work when you're grinding this much. I completely used up 3 masonry grinding wheels and part of a 4th to complete the task. It was worth the effort but was certainly a nuisance to me and the neighbors.

            Today, I poured concrete into every other core of the stand to ensure a solid build. To help strengthen the structure, I placed rebar vertically in each of the corners and one on each side and made sure it poked up out of the core to allow it to embed in the hearth and add more strength to the structure.

            When pouring my foundation, there was plenty of spillover concrete from the leveling process. I broke this concrete off the outside of my form 2x8s and placed the chunks in the bottom of cores to reduce the amount of concrete I would need to pour in. To make sure the concrete made it to the bottom and surrounded the fill material, I added extra water to the point where the concrete was nearly soupy. I figure since the concrete blocks will soak up some of this water it won't cause the concrete in the cores to be weak from being too wet. By the time I was complete, you could already see some of this moisture saturating the concrete blocks as they turned darker around the seams.

            I've worked hard for 4 weekends in a row and my body is starting (actually, continuing) to complain. I'm going to let the entire structure cure and take a week off. My wife and kids were complaining about missing me so I plan to relax next weekend (including Mother's Day) to let my sore body recover and enjoy some much-needed and well-earned time with the family.

            Attached photos:
            1: The structure is complete. It's square, nearly plumb, and appears to be level on every axis.
            2: I put some of my leftover sheathing under the blocks supported by the angle iron. I figure these cores are likely to catch some of the spillover from the hardiboard when pouring the hearth. The sheathing should keep the concrete from pouring out and making a huge mess.
            3: The cores are filled and you can already see the blocks pulling away some of the excess moisture from the fresh concrete. Some of the rebar didn't end up straight when coming out of the cores, so I'll likely have to grind these off before placing the hardiboard of it may not end up level.
            4: The concrete appears to be setting up well and the rebar is ready to embed itself in the hearth.