Couple - Three questions or four

[Carrpond Steve]

I have just finished my coat over my bricks and am now worried about a couple of things.

1. Did I cover my dome with way too much concrete?

I built a 42" round oven with medium duty fire brick each one cut in half for a 4 1/2" thick wall. I have been watching many videos, reading the instructions from Forno Bravo DYI, and now looking at posts on this forum, I am thinking I have too much mass.

I have 1" concrete slab under my brick oven floor and about 2" of concrete covering my brick dome. I am now thinking do I want to use my offset grinder and cut some mass out of my dome before I insulate it. I am not looking to start a bakery; however, I want a quality oven that is quite versatile. I am thinking of pizza, beef and pork roasts, baking foods like lasagna and poultry and who knows what else.

Has anyone done a build such as this and can you help me understand what kind of time it will take to get to seven, eight or nine hundred degrees for pizza. I don't want to have to start a fire 10 hours before my cook. I also understand I may overfire my oven and have to wait for the oven temp to come back to my desired cooking temp. Am I just asking for trouble here? Should I cut out some mass?

2. Covering the dome insulation.

I have not seen anyone talk about this, the folks at INFAB where I bought my material suggested I cover the insulating blanket with foil just under the chicken wire, before I mud. Is this a good idea or will it come with unintended consequences?

3. Waterproofing membrane?

I see everywhere it is of the most importance to keep water/moisture out of your oven, otherwise you will have to repeat your drying fires. My build is outside, and I intend to finish the oven in tile, has anyone used a waterproofing membrane such as one that a tile setter would use in a shower enclosure. I have found a membrane that will work in steam rooms, showers and pools. If this membrane will not cause some problem with the performance or the build I am going to look into the product and see if the product will hold up to the thermal conditions.

4. I used a ratio of 3:1:1:1 of Silica, Hydrated Lime, Portland Cement, and Clay for my mortar to build my oven. Can I use this as my dome cap just over the insulation? My plan is to tile my oven, and this would make a good substrate for my tile.

Thanks in advance for the help. I have attached a photo of where I am currently in the build.

P.S. I am an old guy who isn't even on Facebook, please forgive me if my forum etiquette is not up to snuff. I will definitely take some constructive criticism.
Once I figure this forum thing out, I will share some photos of my build, this has been more work than I thought "like all my projects" and so far, very rewarding. I look forward to the help and I am very anxious to get back to my build.

[JRPizza]

That is quite a bit of mass - do you have good access to cheap wood? I won't comment on heating times as others may have more to offer, but I was curious how much insulation you have between your floor and the hearth?

[Carrpond Steve]

I have 3" Skamol board directly under the 1" slab under the brick floor. I think I am going to move forward with the mass and take advantage of the longer heating and cooling cycles.
I have had a halogen light in the oven for 48 hours the oven started at 130 degrees, for the last 24 hour or so it has reached 165 and stopped climbing. I have had a clear plastic one square foot swatch under a brick on the top of my dome capturing moisture as it leaves the dome over night and this morning I had more moisture under the plastic. I am assuming because it is under the plastic it is in fact moisture that has left the dome and not moisture from the cool night air?

[Giovanni Rossi]

Agree w JRPizza "That is quite a bit of mass"

Refractory mass and insulation work in concert to determine time (and fuel consumption) to desired temp and the slope of the cool down curve.

I think there is some value to extra mass in the floor. It increases to time before having to recharge the floor when doing a lot of live fire baking like pizza.

Just not sure the extra mass on the dome is going to get you better returns on your fuel investment than what good insulation over just the brick layer would have given you.

An area of concern with the concrete layer extending to your slab is that you've created a conduction path for heat around your floor insulation to bleed heat from your dome.

Not sure how practical it would be to remove a band of the concrete at the base and replace it with some perlite or vermiculite concrete??

About your foil question...I believe the consensus opinion on this forum is no.


If you've read enough builds here, you should have concluded that it is inevitable that moisture will find its way into an oven and that the way to deal with that is to provide various methods of egress. Unfortunately, some of those ships have sailed for your build. Since that's the case, I'll let others weigh-in on the waterproofing membrane, but I've not seen that done here. Plus, the primary location of moisture penetration is at the dome, slab intersection. Considering your location, I would seriously entertain building a shelter to keep the rain (and snow if you're thinking about wintertime cooking) off of your oven. Plus, it makes cooking much more pleasant if the weather is less than ideal.

If you've looked at my build, you saw that I did most everything recommended by the experienced builders here to manage moisture. With all that, I still do an easy spring wake up fire to slowly bring the oven out of its winter slumber.

[Carrpond Steve]

You are correct on many things, ships have sailed and I have created a bridge from my oven wall to my concrete slab under the oven. For now I could destruct the lower couple of inches around the oven and install insulation to disconnect the heat flow from the oven to the slab or go with it and see how the oven performs. I am going with the latter, if I can live with the performance I will save myself some work. About the water issues, after many sleepless hours I have decided to work on a roof for all the reasons you cited above.

Thanks for the insite and time you have given to help, much appreciated.

I will be sure to share new developments as they come.