Hello from Sandpoint, Idaho

[Huckleberry Hill]

I've been reading posts here on and off for a few years while thinking of building a WFO. There is an amazing group here.
Originally, I wanted to do my build from scratch but decided not to for various reasons and instead purchased a Casa 2G 90 kit. It arrives today and I'm getting ready to pour my concrete hearth and will soon put the kit together.
My WFO location was not conducive to a trench footing due tree roots I wanted to preserve so I did piers and posts. I know it's not recommended to use wood but I had these treated posts so built the base with them. Here's a few pics of it so far. Cement board and rock veneer will be added later.
Cheers!

[SableSprings]

Looks like your slab base is plenty stout! Form for slab looks good...since it looks like your oven will be outside, now would be a good time to put in a weep hole or two. We've had lots of discussions here about keeping the ceramic board under the oven dry. If you have a little bit of leftover drip poly pipe (1/2" diameter) or pvc, you can drill a 1/2" hole (or two ) in your cement board under where the oven will be located. Push the poly pipe just through the hole and then cut it to just below the projected concrete surface of your slab. Doing this will help you avoid hitting a piece of rebar if you decide to put in weep holes after the concrete hardens (and you need to drill ). Stuff the poly with some stale bread or paper from your cement bags to keep them from being filled with concrete during the pour. After the slab starts to firm up, you can locate the top(s) and make a slight depression around them to help funnel any water out (through the weep holes).

Hope that helps...and if your insulating board ever does get wet, the weep holes will help the water "escape" as you do recovery curing fires. Since bugs may like to make a home in the weep hole (or that nice warm ceramic board), you can use a dab of silicone seal and a piece of screening over the hole from below.

Looking forward to seeing your progress.

[Huckleberry Hill]

Hi mike, thanks for the advise! I was going to do weep holes- but just drilled holes. I like your method much better! I am planning to raise the oven of the slab with cement pavers to help keep the ceramic board dry. Good idea?
cheers
michael

[SableSprings]

Pavers are worth adding to raise the board off the possible dampness of the base slab. Set them with small gaps between pavers that lead to the weep holes. Looking good!

Based on the next post by David S, I'm thinking sheets of mosaic tile might be a better option than pavers. I expanded on this in post #11 below

[david s]

I’m not convinced that pavers are the ideal material for this application. Because they are quite water absorbent. You could seal them but their interior would still be water absorbent and the sealing would make any moisture that did get in that much harder to eliminate. A material that is not water absorbent but provides space between the supporting slab and the insulation would be a better solution. Foamglass with spaces between pieces of it or some galv steel mesh would achieve this.

[Huckleberry Hill]

That makes sense as. Does anyone know where you can acquire foamglass in my area (Pacific Northwest USA).
with the galvanized mesh would you put only that beneath the board? You're talking about the same mesh you would use with a stucco finish?

[david s]

Sorry, no I was thinking of something like 6 mm weld mesh with around 50 mm squares so it would create a 12 mm air space.

[Huckleberry Hill]

David, I don't know what you mean by galv steel mesh. Can you post a picture or link? Thanks


i added 3 1/2 poly tubes for weep holes today. Screened the ends and will trim to just below finish tomorrow before I place the slab.

[david s]

Sorry, no I was thinking of something like 6 mm weld mesh with around 50 mm squares so it would create a 12 mm air space.

Something like this. It is 3 mm galvanised bar, so is 6 mm thick with 45 mm square spacings. In Australia it is commonly known as weldmesh. My wife grew up in New Guinea in the mid 70’s and it was commonly used as security screening, it was known there as “boy wire”

[UtahBeehiver]

FoamGlas - I got mine at Distribution International, they have a branch in Spokane, WA just down the road from you. The key, as David S says, is to make sure the CaSi is not sitting directly on the concrete hearth so it cannot wick moisture from the bottom but you also need to pay attention to possible ingress water points from the top as well.

[SableSprings]

I’m not convinced that pavers are the ideal material for this application. Because they are quite water absorbent. You could seal them but their interior would still be water absorbent and the sealing would make any moisture that did get in that much harder to eliminate. A material that is not water absorbent but provides space between the supporting slab and the insulation would be a better solution. Foamglass with spaces between pieces of it or some galv steel mesh would achieve this.

I've been thinking about the paver option and although they put a minor barrier between the slab and the insulation board, they are concrete and may absorb/transfer moisture more than we'd like. I think David's right in that we can do better. I thought another solution for those who can't find something like foamglas and don't want to chance pavers, would be to buy some of the porcelain/glass mosaic tile sheets/squares to fit on top of the concrete slab, just below the insulation board. No need to grout them in place, so the channels between each of the small tile pieces would remain open for drainage/moist air escape routes to the slab weep holes. Obviously the glass pieces would not absorb water and at about 5 mm thick would provide all the moisture break/barrier needed between any slab moisture/seepage and the insulation board.

I suspect that most tile places would have sample sheets, partial cases, or discontinued patterns that could be had for quite a bargain price. I would guess most families know someone who's got a box of extra shower or backsplash tiles sitting out in the garage that they would love to trade for a future pizza invite.

I put a few pics of a sample mosaic tile sheet below, just so everyone is clear on the type of product I'm thinking would work best here to do the job. Anyway, just a thought...not extra insulation like the foamglas, but much less expensive and far more available as a water barrier. Probably even the bigger single porcelain floor tiles would work well and there are always big broken pieces available for the asking at any place that does tile work...

[SableSprings]

i added 3 1/2 poly tubes for weep holes today. Screened the ends and will trim to just below finish tomorrow before I place the slab.

How did the pour go? The set up looked great...interested to see some pics of your progress.

[david s]

I've been thinking about the paver option and although they put a minor barrier between the slab and the insulation board, they are concrete and may absorb/transfer moisture more than we'd like. I think David's right in that we can do better. I thought another solution for those who can't find something like foamglas and don't want to chance pavers, would be to buy some of the porcelain/glass mosaic tile sheets/squares to fit on top of the concrete slab, just below the insulation board. No need to grout them in place, so the channels between each of the small tile pieces would remain open for drainage/moist air escape routes to the slab weep holes. Obviously the glass pieces would not absorb water and at about 5 mm thick would provide all the moisture break/barrier needed between any slab moisture/seepage and the insulation board.

I suspect that most tile places would have sample sheets, partial cases, or discontinued patterns that could be had for quite a bargain price. I would guess most families know someone who's got a box of extra shower or backsplash tiles sitting out in the garage that they would love to trade for a future pizza invite.

I put a few pics of a sample mosaic tile sheet below, just so everyone is clear on the type of product I'm thinking would work best here to do the job. Anyway, just a thought...not extra insulation like the foamglas, but much less expensive and far more available as a water barrier. Probably even the bigger single porcelain floor tiles would work well and there are always big broken pieces available for the asking at any place that does tile work...

Good idea Mike, tiles would be a better solution as they'll never rust, many also come pre-glued onto a plastic mat with nice even spaces, although the steel mesh is probably cheaper and provides a bigger volume of air space, could be subject to corrosion living in a moist and hot environment.

[bentedesco]

The tile squares are a very interesting option, actually, I was going to go out and buy pavers today. My only concern is if over time my casi board would slowly "settle" down "into" the tiles? I'm not sure if I'm explaining it right, but could the insulation board eventually be pressed down into the tiles and form indentations where the squares are and thus no longer be 5mm off the concrete?

[Gulf]

I don't think that would be an issue as long as there is not too much of a gap between the tiles. I would be conserned about the mesh unless it were a very close knit mesh. MichaelPBoisvert was thinking about using tiles for elevating the insulation on his build. That was last month, I haven't seen any recent updates on the build.