First firing of cream hard clay bricks.

[deevex]

Hi, I have misunderstood the process, I guess I studied in a differant enviroment to your wood fired ovens. I appoligize.

[david s]

Re: First firing of cream hard clay bricks.

Hi deevex,
Yes the 200 C and 500 C points are important, thectrouble is most oven owners want to get their ovens to temp as quick as possible, unaware of the chemical and physical changes. Also when using wood as a fuel it is difficultvto control the temp rise and with flame hitting the apex of the dome while the sides at the bottom are still cold there is considerable temp difference resulting in expansion stresses which are uneven. I always advise a slow heat up even after curing in order to be kind to the refractory, but reality determines folks desire to get it to temp as quick as possible. Many potters boast about how quick they can do a stoneware firing obviously oblivious to the changes taking place.

[brickie in oz]

Re: First firing of cream hard clay bricks.

deevex, you are talking about firing wet clay not firing the oven built with firebricks arent you?

[GianniFocaccia]

Re: First firing of cream hard clay bricks.

My guess is that its prudent to fire one's oven slowly, allowing time for equalizing rests at 100C (212F), 200C (392F) and 400C (752F). If time is a factor, total firing time could be shortened by using more wood (extending the ring) at each stage.

[david s]

Re: First firing of cream hard clay bricks.

deevex, you are talking about firing wet clay not firing the oven built with firebricks arent you?

The same applies to the clay content of the mortar. It is doubtful that you'd get all of the mortar up to 573 C , so it probably never gets truly "fired"

[david s]

Re: First firing of cream hard clay bricks.

This page is well worth reading
What Temperature Does to Clay - How Temperature Changes Clay

[brickie in oz]

Re: First firing of cream hard clay bricks.

Just read that page David, they are talking about wet clay being fired and not fired bricks being refired, or did I miss something?

[Tscarborough]

Re: First firing of cream hard clay bricks.

The processes he describes have already happened in a home built oven. After initial firing and cooling (at the brick plant), the coefficient of expansion for both fire clay, fire brick, common or even facebrick is very small.

[brickie in oz]

Re: First firing of cream hard clay bricks.

Thats the way I read it too.
The thread is confusing and makes you think its the fired brick doing the weird and wonderful things everytime you fire the oven.

[david s]

Re: First firing of cream hard clay bricks.

The same applies to the clay content of the mortar. It is doubtful that you'd get all of the mortar up to 573 C , so it probably never gets truly "fired"

I was actually referring to the clay in the mortar which has not been fired.

[brickie in oz]

Re: First firing of cream hard clay bricks.

Id doubt that the minuscule amount of clay in the mortar would create a problem.
Is so, just make sure the bricks are all angle cut, problem solved.

[david s]

Re: First firing of cream hard clay bricks.

Yes, I was just suggesting that it is advisable to proceed with caution, especially with the first firings. We really push the ability of the materials to cope with the rapid temp increase even though the materials have the capacity to withstand temps. way in excess of that which we fire.The clay content in a 3:1:1;1 poor mans mortar is not miniscule it is about 17%

[deevex]

Re: First firing of cream hard clay bricks.

Hi, I dont mean to confuse you I guess it's more relevent to the wet clay, method of construction, and also wet mortar setting. I have an interest in digging mud from the ground.

[david s]

Re: First firing of cream hard clay bricks.

The processes he describes have already happened in a home built oven. After initial firing and cooling (at the brick plant), the coefficient of expansion for both fire clay, fire brick, common or even facebrick is very small.

When i made my first oven, i built it with a flue in the centre of the dome and had an arrangement to cope with the expanding inner dome where the flue met the outer shell. The height of the inner dome increased by about 2 mm so i would also assume that the dome diameter at the base would have increased by 4mm. This is more than very small and oven design should allow for this expansion. I believe that if you have a thermal break it should be made of a material that has some elasticity like vermicrete.

[david s]

Re: First firing of cream hard clay bricks.

[QUOTE=brickie in oz;113505]David youll have to excuse me but you come across as an alarmist.

Dont fire the oven too quickly or itll shock your oven with catastrophic consequences.
Dont dry too quickly as it will all collapse.
The clay will expand too much and cause the oven to explode.
Curing an oven built of firebrick with a fire too quickly will make the moisture in the brick explode the brick.

My apologies if what I have posted is construed as alarmist, it is only proceeding with caution. You exaggerate what I have posted. I have never said any of those things you mentioned. I only want to provide information gained through experience to assist those who want to build their own ovens. I have seen quite a number of failures, including my own mistakes.