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DougK 04-01-2014 10:45 AM

dome touching outer masonry...
My mason wants the base of his oven dome to butt into the surrounding concrete block (the housing, basically). I'm concerned about lack of insulation, and have read there may be heat expansion differences that could cause trouble. Can anyone shed some light on this subject?


cobblerdave 04-02-2014 01:00 PM

Re: dome touching outer masonry...
The hearth and dome should be completely surrounded by insulation. Under the hearth and over the dome. If it isn't it will be hard to get it to a decent temperature and hard to maintain that temperature. Like most things if it proves difficult and hard to use you'll soon lose interest and will not use it.
Regards Dave
Check out the forno plans its all explained in there

GianniFocaccia 04-02-2014 02:08 PM

Re: dome touching outer masonry...
I wholeheartedly agree with Dave. Insulation is critical.

I am assuming it's your mason building your oven. Ask him what the reasoning is behind his request to butt the dome base directly into concrete. If it's because he feels the dome geometry requires buttressing, that may be legit. There are alternative methods of buttressing without sacrificing insulation. If its because the dome integrity requires buttressing, you may need a new mason.

If he doesn't understand the significance of uninterrupted insulation, don't fold. How 'bout some pics?

DougK 04-02-2014 03:07 PM

Re: dome touching outer masonry...
He feels the dome needs some buttressing. he's backing down a bit - now talking about three 1-brick buttresses at 9, 12 and 3 o'clock. ceramic blanket over the dome, then pack the first course of dome bricks (outer dome to outer housing) with vermiculite/cement, then loose vermiculite over the top.

he's very old school. Took a couple of days for him to understand the need for insulation under the firebricks...

Gladly share some pictures when I get started tomorrow.

thanks guys!

Greenman 04-02-2014 06:17 PM

Re: dome touching outer masonry...
If you have the bricks of the dome touching other masonry then that is where your heat will leak to. Dave and GianniF have it completely right. The insulation (uninterrupted) is critical to getting any sort of decent performance from your oven.

Be interested to see what your mason comes up with.

stonecutter 04-02-2014 06:19 PM

Re: dome touching outer masonry...
Get another mason.

Tscarborough 04-02-2014 08:02 PM

Re: dome touching outer masonry...
Some of the best masons I know (and I know a lot) have no clue on how to build an oven correctly. They are masons, not thermal engineers or ovenbuilders, so they need to be given strict specifications as to how you want the oven built. It doesn't have to be complicated, 2 or three of the pages from the FB plans will suffice to show them what you expect regarding insulation and thermal isolation, as well as the important dimensional information regarding dome height, door height, and flue size and location.

Remember, they may be expert masons, but very, very few have built anything more than a fireplace (if that), and you do not want a funny looking fireplace.

DougK 04-02-2014 10:06 PM

Re: dome touching outer masonry...
Thanks for the input. I've shared a lot of the FB stuff, and he's come around on most. I told him the other day it's my oven and my money, so I don't expect any other issues. Just new to him. The fact that he's also building my Rumford fireplace (very nicely) helps.

Love to share photos soon.

GianniFocaccia 04-03-2014 10:03 AM

Re: dome touching outer masonry...
If the dome is constructed properly, depending on its geometry, there shouldn't be a need for buttressing.

DougK 04-03-2014 11:15 AM

Re: dome touching outer masonry...
Thanks all. We had an hour long review of the project this morning using the FB plans/photos; the result is a change in attitude and a clear plan to achieve what I want. No buttressing, no touching.

Btw, anyone if the Seattle area looking for calcium silicate board (CalSil), West Coast Insulation provided me with 1.5" thick for $1/s.f.
Marine Insulation | Insulation for Boats | West Coast Insulation - West Coast Insulation Incorporated


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