36" build in heart of Europe, Czech Republic

[UtahBeehiver]

A number of builders place cheap ceramic tiles down to raise the CaSi off the hearth with spacing such that leads to weep holes, 2-3 holes should be sufficient. I do not think you need to channel the hearth. A more expensive option is a layer of FoamGlas insulation first, this material does not absorb water but it is fairly expensive and hard to find.

[mrotter]

Yea, foamglass is very very difficult to get here, price would not be that critical, but it is just unavailable. I have also seen someone using aluminium foils placed under/around CaSi to a height let's say 5 cm to create "enclosure". That would perhaps be the way?

By the way, all of this would not be needed if there will be some kind of roofing over the oven right?

[david s]

As the moisture travels away from the heat, the foil under the cal sil board simply acts as a vapour barrier that traps the moisture in. I think a better solution is to provide an exit for the moisture to escape by. Some weep holes through the supporting slab and some tiles for the cal sil board to sit on, do a much better job IMO.

[mrotter]

As the moisture travels away from the heat, the foil under the cal sil board simply acts as a vapour barrier that traps the moisture in. I think a better solution is to provide an exit for the moisture to escape by. Some weep holes through the supporting slab and some tiles for the cal sil board to sit on, do a much better job IMO.

Makes perfect sense. Do you see the importance of weep holes even if there will be roof made above the oven?

[david s]

The need is reduced because you won’t have the problem of possible rain entry. However the initial purging of moisture from the oven, particularly the underfloor moisture that is the hardest to eliminate, still needs an exit path. Depending on your weather conditions the porous materials will pick up moisture from the atmosphere if the oven has not been used for a few weeks. In this case a roof is of no use in preventing moisture. We live in the tropics and during our wet season when humidity is extremely high, even if there has been no rain, the oven will pick up a lot of moisture. You can easily assess this condition by placing your hand on the outside of the oven during firing. It will be hot rather than warm because the insulation is moist and damp insulation doesn’t work particularly well. The remedy is to fire gently for a much longer time (around (5 hours) and the oven’s performance is restored.

[mrotter]

The need is reduced because you won’t have the problem of possible rain entry. However the initial purging of moisture from the oven, particularly the underfloor moisture that is the hardest to eliminate, still needs an exit path. Depending on your weather conditions the porous materials will pick up moisture from the atmosphere if the oven has not been used for a few weeks. In this case a roof is of no use in preventing moisture. We live in the tropics and during our wet season when humidity is extremely high, even if there has been no rain, the oven will pick up a lot of moisture. You can easily assess this condition by placing your hand on the outside of the oven during firing. It will be hot rather than warm because the insulation is moist and damp insulation doesn’t work particularly well. The remedy is to fire gently for a much longer time (around (5 hours) and the oven’s performance is restored.

OK, I made a note, I will buy cheapest ceramic tiles (8 mm thickness, frost-resistant) and will lay them under CaSi. Sides will be completely enclosed with fire blanket+perlcrete anyway.

Do you have any photost of the actuall process where tiles are visible?

Btw just ordered some material for spring - 75 kg of heat resistant mortar, 70 mm CaSi board of required dimensions etc. - will start preparing - cutting CaSi to shape when it arrives.

[mrotter]

I am at 85-90 cm inner diameter (34-36"). What diameter should CaSi layer have? It must be placed under floor + dome side "wall" + blanket. So let's say: 12 cm (side of dome), 6-7.5 cm of blanket insulation on each side. So the actual circle of CaSi should have about 130 cm in diameter, right?

[Gulf]

Check this link out, Hello from Sandpoint, Idaho ,for a good example of using tiles for elevation and drainage.

[mrotter]

Nice photos, thanks.

Additional question: I have about 150 firebricks and I want to make some work ahead and I was thinking about splitting about 60 of the bricks to be used on the dome. I have made some brick works in the past and I want to ask, do I need to cut bricks with tilt/bevel or is it enough to just split each brick in two same halves? I understand that I will need (much) more mortar, but that is not necesarily bad, right?

[Gulf]

....do I need to cut bricks with tilt/bevel or is it enough to just split each brick in two same halves? .....

Beveling firebrick is a relatively new thing thanks to the advent of power tools. Brick ovens have been built without beveling for centuries. Halves with no beveling will be just fine IMO. It's your choice

[mrotter]

Will do, thanks.

[UtahBeehiver]

Like Joe said, ovens can be made without beveling or taper (angle). Just be aware that if you do not bevel you will see what is called and "inverted V" mortar joints in the upper portion of the dome. These joints will be exposed more to higher heat and flame. Attached is a pic of inverted v joints. The inverted v joints can be reduced by doing a partial bevel on the bricks in the interior of the dome. JR Pizza did this in his build..

[mrotter]

Like Joe said, ovens can be made without beveling or taper (angle). Just be aware that if you do not bevel you will see what is called and "inverted V" mortar joints in the upper portion of the dome. These joints will be exposed more to higher heat and flame. Attached is a pic of inverted v joints. The inverted v joints can be reduced by doing a partial bevel on the bricks in the interior of the dome. JR Pizza did this in his build..

Thanks! This is eyes opening stuff. You are correct. I will very likely incorporate "bevelling" into my concept, probably not for first 3-5 rows of dome bricks, but in higher rows, the need will manifest itself. Thing is, that when implementing bevel, the "width" of brick for next row is changed (smaller), therefore leading to unavoidable waste of some brick material + it could be harder to stagger bricks on subsequent rows?

[UtahBeehiver]

The bricks do not need to be beveled the whole width or depth of the brick to achieve a tight inner dome joint only where to two opposing brick conflict (this causes the inverted v joint). The loss of brick material in the scheme of things is relatively nominal. Again, look at JR Pizza's thread. I did a full depth taper and bevel on my build, and the joints are very tight front to back just to prove I could but IMHO it is not worth the effort. Mortar easily can fill the backside of the joints and have tight inner joints at the same time. Also you will not see and inverted v joints for the first 3-4 courses.

[david s]

The wedges you cut off from each brick can be inserted into the gaps on the outside to reduce waste and required mortar.