Sand dome

[Patrick.S]

While I was reading the Forno Bravo plans they mention that building your oven over a sand form is the "old world" way of doing it. My own observation is that many people build at least a third over a form anyway. Apart from some mortar spillage is there a reason a sand form wouldn't work to build the whole dome. I imagine that it could allow for a slightly lower dome height than one built with the indispensable tool, but i might be missing some other issues. If a sand dome is the traditional way of building brick ovens, is there any reason it couldn't still work today?

[david s]

I presume you are referring to using a sand mould to lay up bricks against. A sand mould has the disadvantage of not being able to tidy up the mortar joints on the inside as you build. This job then needs to be done after the dome is completed and the sand removed. It is only cosmetic and wouldn’t really matter if those mortar joints were left a bit rough anyhow. The advantage of using a sand mould as you point out, is that you are not constrained to the hemispherical form. A low dome or even an oval form either in a horizontal or vertical cross section is simplicity itself. Another advantage of the sand dome is that the damp sand helps to retain moisture in the mortar joints, if using homebrew mortar, which is important for its curing. If you use a calcium aluminate mortar this is not necessary as it achieves its full strength in 24 hrs.
If building a cast oven a sand mould it is also an easy method, simpler, quicker and cheaper than constructing inner and outer mounds. You can save quite a bit of sand by piling some polystyrene boxes in the middle and then covering them with sand.

[Patrick.S]

Thanks for your input, David. In your experience, what is the best tool to clean up dried mortar that may have spilled out of the joints? Would a cold chisel be best or something more like a sander? I'm figuring a quick once over inside the dome with something could finish it to a decent standard.

[david s]

Yes a cold chisel or perhaps a paint scraper would be a reasonable choice.