Fire Brick Quality / Chemical

[Honeycomb]

Hi everybody..

At the place, where we're about to buy the firebricks, there are a few times used ovens. Most of the firebricks are giving out a kind of white chemical, it looks like salt structure but it's a kind of chemical, i'm afraid worse than mold or fungus.

The salesman said that it's normal, after the heat and cooling down, the firebricks are sweating humidity but after you fire the oven, they disappear..

Has anyone experienced something like that? Could it be something dangerous for food or something natural about the firebricks and/or about the quality?

I'll be very happy if someone can answer as soon as possible..

[ATK406]

Re: Fire Brick Quality / Chemical

I think I know what you are talking about. It is a kind of chaulky residue/powder. I had the same thing after my 4th or 5th curing fire. I only noticed it in the vent/openning area mostly along the mortar joints but some of it was on the face of the brick too. It may have been present inside the oven too but I haven't been inside to have a closer look.

It would make sense to me that as the moisture inside the brick and mortar vaporizes and escapes from the brick, it might leave a residue of the fine particles that were disolved in the water...You will see similar deposits around the opening of well used tea kettle whistle.

I just wiped it off and never thought about it again. If you can wipe it off, I wouldn't worry about it. Maybe others have experienced the same thing?

Regards,
AT

[Honeycomb]

Re: Fire Brick Quality / Chemical

Thanks for your reply, ATK406.. Meanwhile I inquired with the manufacturers overseas. First of all, among all the people I?ve talked, nobody ever experienced something like that. One manufacturer thinks that it can be Sodium Oxide (Alkali); which for residential firebricks must be lower than %1, if not can be toxic for the food.

I also learned the standards about how the bricks are done. It must be heated over 2300 F (1300 C) and firebrick takes out all the chemicals. After this process, in no other circumstances, including wood fire; the brick can not have any reactions..

However.. some manufacturers take second hand firebricks from industrial; break them down and make firebricks all over again. If this second hand firebrick is not done by the right high heat standards, and/or has absorbed some chemicals that can not get out with this heat. If you use this firebrick in wood oven, it may give out chemical with the wood fire..

Another possibility is about mortar giving out residue after cooling down. But it doesn?t explain how it can be on the face, too.. And I know what I saw, it?s nothing about moisture or mild.. It more looks like a white crystallized chemical.

I?m glad at least I?ve found someone that experienced I hope I get more answers with the real explanation.

[Laurentius]

Re: Fire Brick Quality / Chemical

Hi Honeycomb,

I think we all have seen this to some degrees, some recognize it others don't. Whats your concern? Are you just asking had others notice or do you think its a health hazard? If you think thats its a hazard, I would recommend not allow any food to come in direct contact. As for it reacting with the heat and penetrating the food, I would worry so much about that! You and I should be more concerned about whats in air, coming from our neighboring countries, and our owns as a matter of fact.

[neophyte]

Re: Fire Brick Quality / Chemical

Would it be alright to use questionable firebrick as an underlayment with new fire brick? I have many used firebrick but not sure if suitable for oven. I was hoping to use the questionable bricks under new bricks for extra thermal mass. Does anybody believe that I can do this method without the supposed bad bricks leaching into oven? Or is there a way of sealing the used firebrick? Thank You

[texman]

Re: Fire Brick Quality / Chemical

Are you thinking for using them under your floor for your oven?
If so, it would just add more mass to heat and hold temps. Normal ovens dont need that and you still need insulation there anyway. I dont see how you would be gaining anything, especially since they are questionable?
Texman

[neophyte]

Re: Fire Brick Quality / Chemical

Thank You texman.I just thought that it would add to the thermal mass and would hold heat longer with sufficient insulation below and on sides.
The firebricks that i have are very old industrial bricks and i have used them in outdoor fireplaces.How would I go about testing the bricks for heavy metals? Would you texman or anybody else have further information ?
Please explain why the extra brick under floor brick [ new firebrick] would not contibute to holding the heat longer with more than adequate insulation. Thanks

[neophyte]

Re: Fire Brick Quality / Chemical

Honeycomb, would the problem you write about be a type of efforvesence [ spelling ] a leaching out of soluble salts from either the mortar or brick, i am only quessing of course, but i do know it is a common occurrence in masonry [ brick, block, stonework ] if it is this , not to worry , just clean it and it should be ok, but check with other people to make sure, shame not to use your oven if it is only efforvesence.

[Laurentius]

Re: Fire Brick Quality / Chemical

Honeycomb, would the problem you write about be a type of efforvesence [ spelling ] a leaching out of soluble salts from either the mortar or brick, i am only quessing of course, but i do know it is a common occurrence in masonry [ brick, block, stonework ] if it is this , not to worry , just clean it and it should be ok, but check with other people to make sure, shame not to use your oven if it is only efforvesence.

Has Honeycomb been back since January?

[stonecutter]

Re: Fire Brick Quality / Chemical

Honeycomb, would the problem you write about be a type of efforvesence [ spelling ] a leaching out of soluble salts from either the mortar or brick, i am only quessing of course, but i do know it is a common occurrence in masonry [ brick, block, stonework ] if it is this , not to worry , just clean it and it should be ok, but check with other people to make sure, shame not to use your oven if it is only efforvesence.

Efflorescence forms when moisture evaporates through masonry ...the mortar or the firebrick. If it continues to show after cleaning, then the masonry still contains moisture or it is being absorbed from somewhere.

[texman]

Re: Fire Brick Quality / Chemical

Thank You texman.I just thought that it would add to the thermal mass and would hold heat longer with sufficient insulation below and on sides.
The firebricks that i have are very old industrial bricks and i have used them in outdoor fireplaces.How would I go about testing the bricks for heavy metals? Would you texman or anybody else have further information ?
Please explain why the extra brick under floor brick [ new firebrick] would not contibute to holding the heat longer with more than adequate insulation. Thanks

It will definitely hold the heat longer with the added mass of the old bricks. I think the issue is that the mass of the floor is significantly different than that of the dome. So after firing the dome cools faster than the floor instead of transitioning in conjunction with each other. Normally, the added floor mass is desired for mass production.

No idea how to test the bricks for metals.
HTH

Texman