Air Pockets in the Castable Refractory

Hello BrickWood oven!!
My wife and I poured the 28” cupola last weekend and I started taking down the foam form. Unfortunately I noticed on the outside an air pocket that formed and I could see through it. Can this be fixed by mixing more refractory cement and patching it? Can it be fixed by patching it with refractory mortar? Or do I junk it and start again?
The pic below doesn’t show the void but it’s further back on the left side. I failed to take pic at the time.
Thank You in advance.

Did you patch the holes? If so, was the oven functional?

The reason I am asking is that I just pulled the mold off and I have holes as well.

What did you do?



If you have some pin-holes in your castable refractory… it is NOT an issue. Especially on the exterior which will be covered with Ceramic Fiber Blanket. Only internal holes larger than a pencil eraser should / can be patched.

BUT - if you really want to fill a few holes, simply order a 15lb tub SAIRSET PRE-MIX MORTAR from HarbisonWalker (about $16) and they will ship it directly to your home via UPS. You will also need a 2" or 3" Putty Knife.

Just make sure you apply the mortar BEFORE you start your curing fires as the fires will leave a layer of smoke / soot film that may prevent a good bond.

Next question for both of you… How well did the large foam wedges come out of the inside of the Mattone Cupola’s? I recently did a small design change on the Cupola’s so it would be MUCH easier to remove the inside foam. Instead of one solid chunk of foam, we are now building the form w/ foam sections so they SHOULD slide out with a little elbow grease. And according to CAD, the foam wedges remove 50% of the internal foam.

Can you let me know your thoughts?

Thank you so much for the quick response! I am very relieved to hear that I can patch it up. I think I will try to patch with the left over refractory and a putty knife. If that doesn’t hold, I will order the Sairset and patch with that.

The foam wedges were a challenge, but once I saw that they were is sections, that seemed to make it a bit easier. Looking back on it, I should have made some sort of a hook, maybe from a wire hanger and shoved it into the wedge and slide it out? Maybe that would have been easier?

Anyway, I really appreciate you advice.



1 Like

Hello, I am planning on removing the foam form this weekend. If I end up with some pin holes, or larger holes on the inside of the oven, would there be an issue if I used a little of the black high temp mortar caulk that comes with the Mattone Cupola kit, or a similar fireplace mortar that comes in a caulk tube for these holes, instead of buying a whole tub of Sairset?