I also took my time to air dry the mortar before doing the bakeout (1 whole week). Even then, I kept things around 250-300F for a few hours before going up higher, but nothing more than 400F for the first few firings since mortaring. But I got little bubbles the first time, then more and bigger ones with each additional firing. Some of the mortar bubbles are as large as my palm.
Now that Humpty's insides have been mortared, I've noticed condensation on the mortar almost every time I lift the lid after he's cooled down (say overnight or longer). At first I thought it was due to our West Coast humidity - it rains a lot here. After all, Humpty is kept outside under cover but doesn't get rained on.
However, now I'm wondering if the condensation is due to the trapped moisture that collects on the mortared walls when I snuff out the coals by closing the bottom damper and use the ceramic top. After all, water is a by-product of combustion.
This picture of the dome was taken after Humpty had cooled down overnight after a cook. The shiny sheen is condensation. It's usually wetter near the neck opening but the condensation also extends down into the bottom walls too.
For what it's worth, I never noticed condensation on the bare claypot walls before mortaring the entire inside.
So, I'm thinking that the trapped condensation diffuses back into the "cured" mortar. Then when I fire up again, the water makes steam, which gets trapped in the mortar causing it to puff up and make more bubbles.
One thing about curing the mortar in an electric oven is that it is a DRY environment as there is no combustion happening to produce water (can't say the same for a gas oven).
Because the mortar continues to bubble after each firing and cookout, this tells me it has not fully cured.
- Maybe I have to get the temperatures up even higher? But I did get to about 550F during my last cook. And I've been warned not to take it much higher so as not to crack the claypot further....
- Perhaps the Imperial furnace cement I'm using has different properties than the Rutland brand you're using?
- Maybe I got a bad or expired batch? But I bought 3 different tubs on 3 different occasions... and the mortar's behaving the same wherever it's been applied....
All this might explain why other people's mortar repars are NOT bubbling and why mine IS continuing to bubble... but then maybe not.
Project Humpty: SLIDESHOW
, PHOTO ALBUM
Kamado Claypot, Cobb