Brick porosity

[david s]

I did a test of the brick porosity of one of my firebricks yesterday. The brick was 12"x 9 1/4" x 3" and weighed 9.25Kg dry. Soaked for 24Hrs it weighed 11.5 Kg which is approx.20% I did not remove moisture from the dry brick first and my old spring bathroom scales are not too accurate but it indicates that the brick has taken on a lot of water. This indicates that the brick is very porous and not very vitrified. This quality is desirable to make the brick highly refractory but undesirable in that it will absorb water easily and hold a large quantity. I have read that it is the moist heat that is the WFO's secret, so perhaps the porosity of the bricks is an important factor in the WFO's success in cooking superiority.

[brickie in oz]

Slow day at work was it?

[david s]

No, flat out actually, but it is a topic I've been getting interested in and was hoping someone else might might chime in to give some constructive input into the subject so we can all benefit from increased knowledge. And weighing one brick is way easier than cutting lots of them.

[brickie in oz]

Originally Posted by david s

And weighing one brick is way easier than cutting lots of them.

Why are you cutting lots of wet bricks?

[david s]

I didn't say I was.

[Karangi Dude]

Hey David,
Interesting point you make about the porosity of fire bricks.
When describing how WFO's work, I have often said to people that Gas and Electric Ovens have openings that allows heat and moisture to escape and that there is constant air flow cooking but also drying out whatever we are cooking. But with a WFO (with a proper insulated door) that does not apply. We apply water to create steam when baking bread and meat is allways moist when baked, but the WFO never seems to humid I presume the bricks must absorb that excees moisture.
David I have been cooking for 40 odd years (all styles of food) and I am really impressed with the control and versatility of my WFO.

Cheers Doug

[david s]

I agree, but is it the fuel used or the porous bricks that give it that superiority?
I think also that a WFO cooks with radiating heat rathe than by convection like a standard oven.
Maybe someone with experience with both a steel dome and a firebrick dome may chime in. Although a steel dome with a firebrick floor is still half a firebrick oven.

[Tscarborough]

The ones we carry give a rated porosity of 13-17%.

http://www.wgpaver.com/files/PDF/Fir...heet%20Red.pdf

[david s]

Thanks Tscarborough,
Given the high degree of porosity of fire brick, presumably some containment of water, rather than full saturation, in the brick when laying them is desirable to reduce the tendency of the brick to suck water out of the mortar too fast. Is this a logical conclusion?

[Tscarborough]

Yes, as I have stated a dozen times, the proper amount of water is SSD. Saturated, surface dry. That is to say, the surface will not have a sheen, but it will be damp. Usually, a dip before use is adequate, but in hot (like yours and mine hot, 95+ degrees) and windy, you may have to either soak them and then allow them to dry a bit before use, or, as recommended by the BIA, hose the pile every now and then.

As an FYI most common brick have less than 5% absorbtion, and hard fired face brick are usually far less than 2% in a 24 hour soak test.