Thermal Breaks: Definitely Worth It!

[cleverdick]

Re: Thermal Breaks: Definitely Worth It!

Breaks were mentioned on another thread. Out of curiosity, can you cook on the fourth day?

I know thermal breaks have been discussed on here before, but I just thought it might be helpful to bring the subject into the foreground again, for anyone currently debating whether to go to the trouble of engineering them in.

Can I cook on the fourth day? Honestly, no. The second day maybe. But there are several reasons for this:

(1) My cooking floor has only a 25mm layer of calcium silicate board under it, plus a 10mm layer of lean mortar (6:1). That sits on a 10mm layer of poured floor levelling compound on top of the slab. So yes, I should have used thicker insulation underneath. The dome is covered by CalSil blanket (like FB blanket?), with a 150mm layer of rockwool over the top. Then there is loose vermiculite poured in around the outside, which goes to about halfway up.

(2) It's a really small dome, of about 600mm internal diameter. The dome and cooking floor are something like 50mm thick. So it won't have anything like the same thermal mass as one built with firebricks. (The upside is that it doesn't take as long to fire.)

(3) It's cold here! And damp! It's all very well for people who live in climates where it's 40c and doesn't rain for 3 months to say "my oven is still hot after 4 days". In those conditions mine probably would be, too.

If I'd followed the instructions from the manufacturer, I doubt I'd be cooking even an hour after the fire had gone out. Plus, I most likely would have burnt my nose on the front of the oven!

[Les]

Re: Thermal Breaks: Definitely Worth It!

Breaks were mentioned on another thread. Out of curiosity, can you cook on the fourth day?

[Lburou]

Re: Thermal Breaks: Definitely Worth It!

It sounds like your thermal breaks were real clever, Dick

Congratulations! Very desirable outcome. Well and truely done.

[cleverdick]

Since I am in England, where it's normally cold and damp (like now), I took the extra precaution of building in two thermal breaks - one between the pre-cast dome's arch and an intermediate firebrick arch, and the other between the firebrick arch and the decorative outer arch (over which the front wall is built). Each thermal break is about 1cm, stuffed with soft, fire rope caulking.

I just took some temperature readings with a laser thermometer. The inner arch (part of the dome) was about 250c, the intermediate arch was about 150c, and the outer arch was 40c.

Looking at finished project photos on the forum of a well-known French manufacturer of pre-cast domes, you still see people building the front wall of their housing directly onto the front of the dome! (They tend not to insulate under the floor, either.) Not only do many of them end up with cracked facades, the heat losses must be colossal!