Building 42 in Pompeii, any pearls regarding laying down 2 in FB BOARD beneath firebr

[Zagurskij]

Building 42 in Pompeii, any pearls regarding laying down 2 in FB BOARD beneath firebrick floor?

[Gulf]

My 1st recommendation is to elevate the insulation off of the concrete hearth.

Edit: Moving post to new thread.

[rwiegand]

Lay down 4"?

No one seems to suggest putting a vapor barrier between the board and the concrete. Since water can wick through the concrete and reach your insulation, depending on the enclosure design, that would seem to be a simple precaution. I don't know why it's not done. I didn't think about it in time or I would have put down a sheet of stainless steel under the insulation to create a barrier.

[Gulf]

No one seems to suggest putting a vapor barrier between the board and the concrete.

Well, I know a few of us who have been preaching moisture barriers for several years now. I also now advise elevating the insulation up off of the hearth. Installing a layer of concrete pavers is a quick way to do that. That same moisture barrier placed on top of the pavers would be much beter than a moisture barrier alone. A moisture barrier is great to stop wicking but, it can't stop water that is being introduced from the side on top of the concrete hearth . Any water pooling there will definately be deeper than the few miils thickness that a moisture barrier would be.

[david s]

Lay down 4"?

No one seems to suggest putting a vapor barrier between the board and the concrete. Since water can wick through the concrete and reach your insulation, depending on the enclosure design, that would seem to be a simple precaution. I don't know why it's not done. I didn't think about it in time or I would have put down a sheet of stainless steel under the insulation to create a barrier.

I agree, I‘be been recommending this for years. In my own builds I seal the tops of the concrete piers to prevent water wicking up the stand as well as adding Xypex to the concrete slab to make it waterproof. In addition a hole or two through the supporting slab near the middle will act as a weep hole to help eliminate water if the insulation gets damp. Gulf’s idea of raising the insulation with some concrete pavers is also a good one provided the spaces between them are not too big.

[brad mole]

I am in the middle of my build, a 42” pompeii with 4”” calcium silicate board under the firebricks. I was aware of the problems with wicking water so i decided to put an overlapping layer of aluminium foil down first, i hoped this would act as a barrier but still allow water out if required (through the overlaps) i also made the foil base oversides so i can fold up the edges incase water does pool

i cant say if it has worked yet though, see post 34 of my build thread for pics

https://community.fornobravo.com/for...-pompeii/page3

[rwiegand]

Aluminum in contact with concrete will corrode pretty quickly, so you might want to choose a different material if it's not too late. It's both the alkaline nature of the concrete as well as a possible galvanic reaction between the steel rebar and the aluminum if the concrete is damp.

[brad mole]

Too late im on the third course now

[SableSprings]

I agree, I‘be been recommending this for years. In my own builds I seal the tops of the concrete piers to prevent water wicking up the stand as well as adding Xypex to the concrete slab to make it waterproof. In addition a hole or two through the supporting slab near the middle will act as a weep hole to help eliminate water if the insulation gets damp. Gulf’s idea of raising the insulation with some concrete pavers is also a good one provided the spaces between them are not too big.

Just to further enforce what David S noted (I know you are past the point of changing/improving your moisture barrier), I thought it was worth putting in a link to a post (#22) with pictures of my stand showing how water does wick up the CMU (concrete blocks). The last picture in the post's attached pics best shows the dark stain (of water) moving up from my slab.

https://community.fornobravo.com/for...509#post387509

[brad mole]

Im panicing a little now about mine only having aluminium foil down, its too late to get anything else under so does anyone have any ideas for other ways to give me the best chance to keep water out?

I am thinking i will put some sort of silicone bead around the base to stop any surface water seeping in, i will also be covering the dome with vermicrete and either waterproof render or brick slips. my worktops i havent decided yet but i will be butting them up to the dome and probably sealing with silicone again. I was hoping to not have a canopy over the oven but i think i will do now to keep the rain out. Do you think this will be enough to keep moisture out of the calsil board?

Also what happens if it does get wet, is it just that it will need regular firing to drive the moisture out and no perminant damage will be done?

[UtahBeehiver]

I can't remember if you have weep holes in the hearth or not. If not, you can still drill a couple from the bottom side of the hearth so any water getting in can egress out. If water does migrate in, there is not permanent damage, it just the the CaSi will not perform well until dried out again (which is a pain in the #$%) but not the end of the world. You just have to do some drying fires to dry out the CaSi. By sealing the ends you do risk forming a basin for errant water to sit if you do not have weep holes.

[Gulf]

Brad,

Don't panic..You are in the same boat as 95% of this forum that did not include a moisture barrier or elevate the insulation.. Myself included . Though, I now (highly) recommend both. I also highly recommend a roof over the oven. If you do a roof over the oven, extend it out over the entry to allow yourself a dry work area. Aside from it calming your fears over a wet oven, it will greatly extend the number of days per year that your oven can be comfortably operated.

[brad mole]

great thanks for the reassurance guys!, i dont have weep holes as of yet but is it just a case of drilling from the log store underneath up into the slab until i just poke through into the calsil board in a few places? I think i will definitely build a canopy over the roof eventually and just keep it covered as much as i can until then

[david s]

it is far easier to cast them in when laying the slab, but drilling up from the bottom will work.

[david s]

Brad,

Don't panic..You are in the same boat as 95% of this forum that did not include a moisture barrier or elevate the insulation.. Myself included . Though, I now (highly) recommend both. I also highly recommend a roof over the oven. If you do a roof over the oven, extend it out over the entry to allow yourself a dry work area. Aside from it calming your fears over a wet oven, it will greatly extend the number of days per year that your oven can be comfortably operated.

A roof is the best solution to keeping your oven dry and if you do have one then waterproofing the exterior of the dome is unnecessary. This allows the dome to breathe. If the exterior is waterproofed moisture is also trapped in. We live in the tropics and after prolonged humid weather even if it hasn’t rained the oven still picks up significant moisture making the exterior hot to touch. In that case not even a roof would prevent the moisture getting in.