Insallated hearth - Is a water barrier needed?

[towersurf]

Hello, I finally started my 42" pompeii build last week and Im a little unsure of how to proceed so Im hoping someone can point me in the right direction. Ive built the hearth on the block stand and poured a 4" vermiculite - concrete mixed at 8:1 on top of the hearth. Next I will add 2" ceramic fiber board and then start the fire brick oven floor. My question is, should I put some type of water proof render on the vermiculite concrete before I add the ceramic fiber board? My build is in a hot and humid tropical climate and I plan on encasing the oven in a brick enclosure. Im new to posting so let me see if I can attach a photo of the hearth and insulation. Thanks for any advice you can give.

[UtahBeehiver]

Looks like a good start. There is one concerning issue is the Vcrete ratio on the hearth. 8 to 1 is usually used for the dome insulation since this high of ratio of Vcrete is not structurally strong, It is normally 5 to 1 on the hearth. So there is a concern about load from the dome as well as the brick for the enclosure not having a solid enough base. You need to think about this a little. Wet insulation is on the the biggest oven performance issue problem. A waterproof layer can also keep any water from egressing as well. Weep holes are suggested in the hearth. But being in a brick enclosure minimizes water working it way in as long as you flash properly.

[towersurf]

Thanks for the feedback UtahBeehiver. I have learned alot from your posts over the years. Going over my notes I see that the ratio of Vcrete was 7:1 not 8:1 as I had posted. Still not the 5:1 I should have done. I could remove the Vcrete on the edges where the brick enclosure will be built so that its weight is on the concrete hearth but that still leaves the weight of the oven on the 7:1 Vcrete. If you guys feel that its still too great of a concern, I would appriciate if you could let me know any suggested options, even removal if necessary. On the other hand the Vcrete did set up very well and feels more solid then I had expected. Great advice on the weep holes. I'll add them once I remove the forms from under the hearth. What is a typical waterproof layer that oven builders have used? I really appriciate all the advice forum members can give and please have pacients with me as Im sure Ill be back asking for advice throughout the build.

[UtahBeehiver]

I am going let you decide and evaluate loading of brick walls on the dome and the enclosure. Attached are some data on various ratios of vcrete.

[towersurf]

Thanks for the physical properties document, it helps me better understand the loading that can be placed on the Vcrete. By my estimates the surface area of the first course is about 658 square inches and the weight of the brick in the dome would be about 1600 pounds so Im looking at about 2.5 PSI on average. A 7:1 Vcrete mix has a compression strenth of 125 to 140 psi so I should be OK.