The slab dimensions listed below are 8 " wider than the dimensions of your concrete block stand, providing you with 2" for finish material, and a 2" reveal on either side of the stand. The slab is also 10" deep, allowing for 4" in the back (2" finish and reveal), and 6" in front (the additional space makes a nice edge for your wood storage). The foundation slab will also be used to support forms that you will use during the hearth slab construction The finished top of the slab should be 2"-3" above ground level.
The recommended dimensions of the foundation slab and block stand for the size of your oven are as follows (check back for more sizes):
Click on the building material pages to see a list of what is required to construct your foundation slab.
Lay a 3" base of pea gravel (or crushed rock), compact the rock (Photo 2), and cover it with a layer of 6ml plastic sheeting to stop the slab from wicking water.
Place a sheet of wire mesh inside the foundation frame, and install a two piece grid using 1/2" rebar (#4) set 4" and 8" inside the foundation frame. Tie the rebar together with tie wire, then set the wire mesh and rebar half way up the pad (2 3/4"), using either rebar stand-offs or fragments of brick (Photo 3).
Mix your concrete (Photo 4), then pour (Photo 5) and level. Use a 2"x4" to screed and level the concrete, then finish to a smoothness that works for you as the bottom of your wood storage area. Allow the slab to cure for a day or two.
You are ready to continue to the Block Stand.
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The foundation work on this oven was done in 8 hours.
Hints and Tips
Compare both diagonal measurements of your foundation frame to ensure that your foundation is square. Double check that your foundation really faces the exact direction you want you oven to face.
The volume of concrete in the foundation can be heavy (40 80lb bags or more), and mixing it by hand in a wheelbarrow might use up energy and time that will serve you better later in the project. Rent a mixer from Home Depot, and ask a friend (or pay a local teenager) to help you mix and pour the slab.
Remember that while the slab has to be square, level and structurally sound to get your oven off on the right foot, it will never be seen. It is worth saving your best finish work for later in the project, and don't be afraid to go fast at this stage.