Dome

[EricBrick]

Hi, I build my first real brick oven this past summer 2025. Using the Pompeii Oven Plans.
My issue is that after the dome was make i waited about a week then started my five fires. my last fire i saw in some places that smoke was coming through between the Heat Stop 50 Refractory Mortar and the bricks. So i put a layer of Heat Stop 50 Refractory Mortar over the dome hoping that would solve the issue. Well the layer of Heat Stop 50 mortar is coming off the dome.
My Questions are.
1) why is the mortor coming off?
2) can i put the installation over the dome even though the smoke is coming through the cracks?
3) is Heat Stop 50 Refractory Mortar - Dry Mix: Fire-resistant mortar ok to use over the dome, then put the installation, chicken wire, normal mortar?
4) If i use a liquid form of Heat Stop 50 to fill the crack will that help?
thanks
eric

[david s]

Hi Eric,
I suspect that you’ve gone at it a bit too hard. In the construction there is an enormous amount of water added and only a week of curing does not allow wind and sun much time to dry the oven, weather dependant of course. Secondly, the drying fires are better done with the oven insulated to reduce the big difference between the inside and outside surfaces which of course also lead to a big difference in thermal expansion. If it were mine I’d be continuing low and long fires to eliminate moisture. You can check this by throwing a large sheet of plastic over the dome to see if moisture is condensing under it. When most of this has gone you can seal up any cracks with the heat stop, insulate and then proceed to do more fires building up to decent cooking temperature to get

[EricBrick]

Hi David thanks for getting back to me with this info. i will try this and let you know what happens
thanks eric

[SableSprings]

Your mortar probably didn't stick because the bricks sucked out the moisture too quickly to form a bond. Try going over the bricks with a wet sponge before applying the mortar (I'm assuming you are using homebrew or bagged mortar here). As to the cracks, it is a rare build that doesn't have them. Normally the oven interior cracks are much less evident simply because the design has the bricks stacked so you don't have mortar joints showing (which is where the cracks occur). Your dome literally expands and contracts during firing/cool down and the mortar joints are what gives. Since you have aligned your brick joints instead of staggering them, your inside cracks will be more evident. Not to worry...that's the beauty of the dome design! When the oven cools, the dome structure "settles" back to it's original form and the cracks close.

Because of the brick stacking to create the dome, the mortar joints are obviously larger on the outside. Filling the larger outside gaps/joints simply adds to the heat retaining mass and because the dome is covered with insulation and an outside, cosmetic shell...you'll never see those big cracks open & close. By the way, heat stop mortar usually does not fully set at the pizza oven temps nearly as well as homebrew or just plain mortar.

As David advised, do plan on doing your drying fires with the insulation layer on to reduce inside/outside temp variation. Drying fire mantra is to go very slow building temps, you'll be surprised how hot the dome top gets compared to the lower sides with just a couple small sticks of wood. Better to start initial fires with a few charcoal briquettes (low & slow wins!)

Hope this helps, relax...it'll be fine

[EricBrick]

SableSprings
Thanks for responing to my issue.
I would like to write down the steps to make sure i understand everything.

1) i will do what David recommend about putting the plastic over the dome
2) then wet the bricks with sponge.
3) Put the Heat Stop 50 mortar over the whole dome or just the cracks?
4) Insulate
5) Chicken wire
6) 2" Bagged mortar over the whole dome
7) Heat oven slowly or put my decorative tile stone over the dome?
thanks

[SableSprings]

The heat stop mortar is not necessary and does not set at our oven temps (and it's pretty spendy for minimal return value...IMHO). Just bagged mortar over the dome's exterior is fine. It will fill in the cracks and allow you to shape the outer dome a little more smoothly. Embed some hooks or eye screws in a little thicker ring of mortar around the dome base, A little air dry time here is good. Lay your blanket insulation over the dome and secure it with wire or mesh...using the embedded hooks/eye screws to secure the wire. When your insulation blanket is on, you can start doing a couple days of very low heating. The blanket helps reduce temp variation within bricks during firing schedule as well as allowing moisture to escape.

Just a few charcoal briquettes-heat beads is all you need, you'll be surprised how hot it will get! Using just a few briquettes. Another advantage using them is you can move them around on the floor for more even heating. A couple of low & slow days this way before you start the gradual, week-10 day long process of drying/heat fires bringing the dome up to pizza temp operating range is recommended...there can be a lot of water contained in a new build. After you've gone through the drying/heat cycle schedule you can put on the outside render/mortar coating. You don't want to do this until AFTER all the moisture has been driven out. Your step 6 just needs to be done very last so the mortar and tile won't block the moisture's escape path

Hope that helps!

[david s]

SableSprings
Thanks for responing to my issue.
I would like to write down the steps to make sure i understand everything.

1) i will do what David recommend about putting the plastic over the dome
2) then wet the bricks with sponge.
3) Put the Heat Stop 50 mortar over the whole dome or just the cracks?
4) Insulate
5) Chicken wire
6) 2" Bagged mortar over the whole dome
7) Heat oven slowly or put my decorative tile stone over the dome?
thanks

1. No. The plastic sheet test goes on after you’ve insulated. An alternative is to use a simple garden moisture meter. Firing an uninsulated oven is a recipe for thermal shock cracks.