42" Pompeii - Florida

[TomYork]

So it looks like I screwed up the template I used to pour the insulation layer and oven floor. I'll just have to add additional layers of mortar on the outside to even it all out. I removed a brick in the middle of the floor to temporarily throw in a wood insert to support my trammel. My next step is to figure out the front arch / inner tapered arch. I've looked at a variety of posts but still somewhat unclear on where my front opening arch should start etc. Also, I'm just using a wood trammel. I haven't seen anything indicating after what courses I should be cutting the trammel down to account for the lower height dome.

[david s]

I got to thinking about permeability so did a little test of how much water some calcium silicate board would take up. I weighed a piece first, then soaked it in water, not for 24 hours, but for 1/2 hr by which time no bubbles were rising from it and it was just floating with around 0.5mm above the water surface. I figured that was probably sufficient and I removed it and weighed it again. The difference in weight indicates an increase of 250%. (135-35=87 87/35=250%).
I have left it in the sub and wind and will repeat daily weighings to see how it dries. I think this is a worthy and instructive test.

I've completed the cal sil drying experiment.
As previously posted the calsil took on 87 g of water from its starting point of 35g. The attached graph shows how it dried back to its original weight and condition in just 3.5 days.

During drying it was elevated from its base so 3 sides were exposed to sun and 4 to wind.

Bearing in mind calcium silicate covered on the base and sides, or totally encapsulated would take way longer to dry. The piece was restored to normal condition when dried again with no apparent loss of strength.

This simple method of testing porosity can also be used to test bricks

[rsandler]

No, you don't need to mortar down the first ring of bricks. The considerable weight of the dome will keep them in place. I'm not sure about perlcrete, but with CF or CaSi board insulation, you couldn't get a good mortar bond anyway, so it's clearly not needed for the structure of the dome.

Note that since you already have cut a ring of flat-laid bricks, you don't need a half-soldier course, and it would be a little unusual to have one. Usually that would be the very first course, directly on the insulation. I used a half soldier course in both my ovens, but the course went directly on the insulation. Current trend seems to be to skip the soldier course and just do a flat course or two before starting the curve of the dome--as you already have started doing.

[SableSprings]

Not necessary to mortar down the outer cooking floor bricks to the base insulation, the dome weight and outer insulation/render shell will keep everything from "walking away". Also, you don't need to mortar the first perimeter chain (row) to the floor bricks...just ends. Remember to stagger joints between the chains as you build up...it will mean some half or quarter bricks in most chains.

Start in the back so these partial bricks will tend to be closer to the opening (purely for aesthetics ) and set at least one brick in for " tomorrow's chain". This last brick of the day gives you an anchor point for tomorrow's work.

I like how you tied your entry bricks into the herringbone main cooking floor pattern, looks great to my eye.

[TomYork]

Should I be mortaring down the outside ring of bricks before laying my half soldiers on top?

[david s]

I got to thinking about permeability so did a little test of how much water some calcium silicate board would take up. I weighed a piece first, then soaked it in water, not for 24 hours, but for 1/2 hr by which time no bubbles were rising from it and it was just floating with around 0.5mm above the water surface. I figured that was probably sufficient and I removed it and weighed it again. The difference in weight indicates an increase of 250%. (135-35=87 87/35=250%).
I have left it in the sub and wind and will repeat daily weighings to see how it dries. I think this is a worthy and instructive test.

[david s]

The degree of permeability of different tiles can vary considerably, but most ceramic tiles have been vitrified almost to the same degree as porcelain tiles. Vitrification occurs as the silica content begins to turn to glass. This process occurs at higher temperatures over 1000C and can be increased under the presence of certain fluxes which lower the melting point. Generally clay bodies fired to stoneware temperatures 1230+C have vitrified sufficiently to become totally waterproof, while clay bodies fired to Earthenware temperatures 1030-1200C only attain a waterproof quality if glazed. Clay bodies fired to porcelain temperatures 1300+C are also totally waterproof, but need a low silica content and very low levels of fluxes to prevent the clay body from excessive distortion caused by it melting.
The nature of heat loss, as we all know from firing our ovens, is that the higher the temperature the greater the heat loss and higher the input required. And the graph is not a straight line. More than double the energy used for stoneware firings is required for porcelain firings.

To test for permeability, weigh a dry tile then soak it in water for 24 hrs the reweigh again. The difference in weight will give you the quantity of water absorbed. I think you will probably find it is negligible.

[TomYork]

I ended up breaking up a bunch of leftover tile I had so there were a lot of smaller channels. I ended up using weed mat as I had 50 yards of that just sitting around as well. Seemingly I didn't have any issues but I don't have a lot of visibility; only time will tell. I also ended up using ceramic tile, hopefully that doesn't make difference.

[david s]

Aluminium insect screen might be a better solution than weed mat as it’s relatively stiff and would hold up the wet vermicrete better. But it probably just depends how wide you make the tile gaps.

[TomYork]

Thanks for responding Mike. Here is where I'm at now. No mortar was used in the oven floor but i feel like the outside blocks should be mortared down right? Everything is just sitting there by gravity right now.

[SableSprings]

Yes Tom, the porcelain tile is impermeable to moisture and the gaps between tiles provide channels for moisture to "find" and escape out the weep holes. Using some sort of mesh overlay keeps the 5:1 insulated concrete from shutting/filling those escape channels. The reason I like to promote the mesh backed mosaic tile squares is the gaps between tiles is well protected when the sheets are laid upside down. Using the tiles as you have works great as long as you are "protecting" the gaps from being filled. Sorry I didn't get you this answer earlier, but it definitely looks like you already had it figured out.

Looking good and excellent work on sloping the hearth to encourage moisture away from your build.

[TomYork]

I drilled a few weep holes and have to add some more tile, but want to make sure this is what you guys are talking about below the 5:1 perlite / portland cement mixture. The hearth is slightly sloped back to front so I have 3 weep holes near the oven landing. Once the rest of the tile is added I plan on covering the entirety with landscape fabric. Thanks.

[WaterDog]

Thanks for confirming. Will incorporate into the plan.

[david s]

Aluminium insect screen is another option. Cheap and easy to cut, but stiff enough to hold up the vermicrete over a substantial gap.

[UtahBeehiver]

Yes, same stuff. Something that is permeable to transmit any water that gets in there but to keep the pcrete mix from blocking the channels to the weep holes. Sometimes, some smaller tiles have a fine mesh backing that some builders have placed face up but you can't tell for sure if this works or not after the pour.