Friday, 24 January 2014

Building a wood fired bread and pizza oven - First curing fire

In the last couple of days we have made significant progress on my our wood fired bread and pizza oven. The final bit of cast refractory needed to be finished as early as possible as it needs at least 24 hours to dry out at 20 – 30°C before it can be cured at higher temperatures. This last bit of cast refractory covers the reducer arch and brings it up to the height of the door lintel. On the centre of these two components will sit the chimney.

pointing the inside of the oven

After all the vibrating of the cast, refractory is completed. We are confident that the reducer arch temporary supports can be removed. This then allowed just enough space for me to squeeze in and do a little pointing and cleaning up any unwanted mortar.

The main bits of brickwork have been heated for a few days now with an electric heater. The temperature has been gradually increased until for the last 24 hours the brickwork was held at around 40°C. The small amount of mortar used for pointing quickly dried out and so this evening I decided it was time for the first curing fire. The first curing fire was started, very small initially and then increased in size until a reasonable amount of embers built up.

For the first hour the inner surface temperature was kept to less then 120°C, this was at the point directly above the fire, then in the following 3 hours the temperature was gradually increased until most of the inside of the top part of the dome was at around 160°C. The highest surface temperatures reached were directly above the flames and were no higher than 220°C. At the front of the oven, around the chimney transition, where the refractory was only cast 24 hours earlier, the temperature did not exceed 90°C. This is in line with the curing protocol provided by PCO the manufacturer. The final temperature reached on the outside of the dome brickwork was 80°C. This was my target temperature for the day as it is the maximum surface temperature for the extruded polystyrene that is currently cladding the outside of the oven.

Monitoring internal surface temperatures using an infra-red thermometer 

Buried in the hearth of the oven at the hearth / insulation transition is a thermocouple. The temperature reached at this point, after 4 hours of gently firing was 46°C. I expect this continued to rise for some time after I wrapped up the oven and stopped monitoring in order to come inside and write up this post. It is -10°C outside at the moment, so I am glad to be finished for the night and inside drinking a hot coco.