curing temp question

[tulowulo]

I have been curing my oven for the last week and I'm using the low, long and slow method. The first 4 fires I used lump charcoal and increased by temperature 100 degrees each day. I was taking temperature readings with an inferred thermometer on the brick at the top of the dome and then on the sides as well. On day 5 I started using small pieces of wood and kept the fire going making sure not to exceed the target temperature.
Now that I am using wood I'm not sure when to take the temperature reading. If I take it while the flame is licking the top of the dome it quickly reaches 600 + degrees. When the fire dies down a little and I take a temperature reading on the dome it reads closer to 500 degrees. My question is do I take a temperature reading when there is a flame or wait until after the fire has died down a little. Is it the temperature of the brick that needs to reach the desired temperature or is it the peak temperature of the fire.

I'm also looking for advice about the best way to finish the outer dome.
The hearth is insulated with 2" thick ceramic fiber board which I understand should not get wet. I put a layer of the Forno Bravo waterproof mortar over the entire dome before insulating. There is 2" of ceramic blanket insulation covered with 2" of pcrete mixed 4:1. Over the top of this I was planning on using an acrylic stucco. I understand the acrylic stucco is flexible and less likely to crack but I've also heard that it will eventually crack making it no longer waterproof. Should I put another layer of the waterproof mortar over the pcrete before applying the stucco?


Any information you can provide me with would be greatly appreciated. Thanks!

[david s]

The colour of the vermicrete layer indicates that it is still very moist. It is usually a very pale grey colour when most of the water has left the surface. A 4:1 vermicrete is a very rich mix, with poorer insulation value than a leaner brew as well as taking longer to dry due to a lack of air spaces between grains. They're all filled with cement. I recommend a week of drying (at least) before attempting any fires. Try to keep direct flame impingement off the dome as the difference in temperatures is what creates the damage. If you shoot the temperature at the base of the dome you'll understand what I mean. The crown of the oven will dry first and then create much faster heat up of that area the next time you fire. Waiting a day or even two to allow moisture to migrate back a bit is also a pretty good idea, but really hard to do when you are getting keen to finish.

I hope you have some decent foundations on the downhill side of your oven, or you may have some leaning problems down the track.

[Gulf]

You did good by starting with the charcoal method. However, you will never get an accurate temp while there is a live fire in the oven. The first live fires should be very small, trying to keep direct flame impingement off of the dome. That means just adding a few twigs at a time. To get a temp using live fires, there are two things working against you. First, the live fire is delivering radiant heat directly to the brick surface. The surface is super heated but the back of the brick is no where near that temp.The other is the draft air being pulled in to the oven. Once the flanme is out, It will cool the surface of the brick fairly quickly, so getting an accurate temp is still difficult to get.

Here is where a door (insulated or not) comes in handy. Once the flame burns down to coals, close the door for 30 minutes. Then remove the door and get a quick temp with the IR. That will get you at least in the ballpark.

"Forno Bravo waterproof mortar"?

[tulowulo]

David, Thanks for the quick response.
The picture I posted was taken the day we applied the pcrete and it has been more than a week since then. It is now that pale green color that you speak of. I tried to do a leaner mix with the pcrete but found that it was impossible to get it to stick to the chicken wire so I added more portland cement until I could get it to stick. I'm not sure what I was doing wrong and hope that it doesn't affect the insulating properties too much.
Great info on waiting a day or two between firings. The oven holds the temperature pretty well and I wasn't sure if I should wait until it cooled down to ambient temperature before starting the next curing fire.

As for the foundation on the downhill side, there are four 4" x 6" PT posts over 8 liner feet set in 3' of concrete holding the pressure treated wall. Keeping my fingers crossed that it's enough.

[tulowulo]

Gulf,
That is just the information and advice I was looking for.

I've had a door in place and fire is just a few embers. My top of dome reading is 404 and the row of bricks just above the soldier course is about 370.

The information that comes with the Forno Bravo mortar says that it is a waterproof mortar.

[david s]

Ok, all sounds well in hand. Folk nearly always have trouble applying the lean vermicrete brew the first time. The secret is getting the correct amount of water in the mix. It is hard to get it to stand vertically at the dome base and you’d swear it’s not going to harden enough, but it does.You’ve got what you’ve got, it will still work, but take it slow. Roast some chickens for a while, use the heat from the drying fires, but resist going to pizza temps. You will probably notice a persistent black ring around the base of the dome. This is indicative of moisture in that area still. Also try a sheet of plastic over the dome during firing to see if moisture is still condensing under it.

[tulowulo]

Just for informational purposes. This is what came in the bag of Forno Bravo mortar.

[Gulf]

Waterproof. Non water soluble.

To me that means that it wont dissolve if it gets wet after curing. It will still allow moisture to escape imo. That is a good thing.

[tulowulo]

It will allow moisture to escape but will it allow moisture to penetrate? I interpreted it to mean that water would not penetrate. Of course that would only be true if it didn't have cracks.

[Gulf]

I will yield to any of the engineers on the forum. But, “non water soluble” doesn’t mean that it is a water proof barrier. A water/vapor proof barrier would be a bad thing for a cladding imo