insulated floor question

[johnedm]

i'm am planning to mostly follow the pompeii oven plans. i'm installing it outside. I read somewhere the fb board shouldn't get wet, but lookin at the plans, it seems it would be exposed to water from rain (through the oven door and maybe vent).

instead, I planned on using concrete with vermiculite. looks like the structural concrete is supposed to be 3.5" and the light concrete 4 inches for a total of 7.5 inches. then, with the 2.5" fire bricks on top of that i'll have a total thickness of 10".

unfortunately, I also plan to put a gas burner in there, which only has 7 7/8" max clearance. how do people do that?

couple ideas:
1. don't worry about the fb board, it is fine to get wet? or design it in such a way as to not get wet?
2. use angle irons spanning from one side of the blocks to the other in the middle of the oven (for extra support), then pour the concrete only as thick as the angle irons right below where the oven will be (still with rebar, etc), then fill in that area with vermiculite concrete.
3. something else one of you fine ppl will come up with.

thanks,

john

[david s]

All concrete is porous to varying degrees, depending on the porosity of the aggregate used, proportion of cement and additives used. Generally the denser the concrete, the lower the density. There are additives you can use to reduce porosity, but a5:1 vermicrete is pretty porous. Likewise other insulation materials eg cal sil board has similar porosity to a 5:1 vermicrete. There is a water resistant cal sil board, but I think it’s pretty expensive. Not available to me, so haven’t tried it.

For piers wider than that recommended in my build, I suggest using 50 x 50 x 4mm galv. angle as shown in the pic. Making cuts in the blocks with a diamond blade on an angle grinder is very easy. This way a thinner supporting slab can be used.

[johnedm]

thanks so much for the help!

just curious, how do you keep your fb insulation under the floor dry? or is it ok to get wet?

[david s]

I think a lot depends on your weather conditions. Obviously a roof is the best solution, but that requires considerable labour and expense as well as compliance to building regulations. Next is a dog kennel style oven which can shield quite a lot of rain entering the mouth better than an igloo style. Also it’s not only rain but very high prolonged humidity can get into the oven even if it’s perfectly sealed. In practice most ovens are out in the weather and it’s fairly rare to have to do repeated prolonged drying fires.
If you want to explore waterproof/water resistant calsil board, that could also be an alternative solution

[UtahBeehiver]

Thermo Gold 1200 is water resistant CaSi and Thermo Gold 12 is not water resistant. You can also look at a product called FoamGlas which is a water proof insulation material which could be the first layer against the hearth but it is very difficult to find in the USA now. You can also add weep holes and scrap floor tiles as the first layer.

[johnedm]

thx so much for all the responses... I will definitely be using the angle iron under the stand floor... and also, will look for the thermal gold 1200... all that said, I do live in the phx area, which doesn't get much rain or humidity... my oven will be enclosed with waterproof stucco... only the door and vent will be open... the vent will have a cap and I can keep the door closed when not in use (a good idea regardless due to the number of critters we have in our area)... I would guess that i'm likely over-thinking this part...

[Giovanni Rossi]

Read through mongota 's build https://community.fornobravo.com/for...-s-42-ct-build

He used a product called RedGard as extra protection for the CaSil under the landing and provided a 5 yr update as well. I would have used it, but my design was different. However, I used it in other ways. You definitely want to add the tiles and weep holes as Russell suggested. Better to plan to have an escape route for water and moisture infiltration than to depend only on keeping dampness out.