Fire Clay Substitute

[Gulf]

Here is a link to an old post that may help.

[JRPizza]

Hi JRPizza. But what is the tool you used to cut the curve? Forgive my lack of tool knowledge...but I cook a mean pizza!

I used a standard wet saw with a 10" blade. The cuts I show were made in several passes which gives you a faceted curve, but a curve nonetheless

[JRPizza]

Edit - I just read the post Gulf linked to - what I was trying to say but much more clear!

[Karyn B]

Thank you JR Pizza! I am looking forward to the effort. So far, so good. Starting the layout of my arch today.

[shanxk8]

The OP just wanted to know what to substitute the clay with for the sand/clay underfloor leveller. This thread has taken on a whole new direction.
The term "fire clay" is used in the US for any cheap powdered clay used in the building industry generally as a mortar improver. To a potter the term "fire clay is a totally different animal. It is a clay that is designed to withstand extremely high temperatures, (very low in impurities and fluxes, large clay particle size and high in alumina), expensive and certainly way beyond the needs of WFO builders, in terms of service temperature. A powdered clay has extremely small particles and is not cementious, i.e. it does not react chemically at ambient temperature (that begins at 573 C), so it should really be considered an aggregate in a mortar or concrete mix. Because the unfired clay particles are so small they induce shrinkage (typically on its own up to around 10% wet to dry) particularly if used in a large proportion in the mix. Once fired and crushed the particle size is increased enormously and the shrinkage proportionally reduced. This stuff is called grog not fireclay. (well it could be fired and crushed fireclay). The slurry left by the brick saw is also fired clay but the blade cuts it so fine that the particle size is far smaller than crushed fired clay (grog). However the particles of the saw slurry are still way larger than most unfired clays and this would explain why it works so well as a mortar addition with a lower shrinkage.
ps. stay away from Bentonite as it has extremely small clay particle size and has a very high shrinkage rate.

David, I've been collecting my cuttings from bricks for use in home brew for when I run out of high temp mortar (& to fill the joint gaps on the outside of the dome and use on the outer arch). If using the cuttings, do you just replace the 1 part fire clay, with 1 part cuttings. And then still use the same ratio for other components (sand, lime, cement)? I ask because I wonder if some of the cuttings are sand, and then should reduce the amount of sand to include.

Thanks,
David (another David S in fact )

[david s]

Yes, just use it as a substitute for the clay in the recipe. As it will be a sloppy wet mix it’s volume is greater so just adjust for that.

[shanxk8]

Thanks David

I've got mine in a big-ish Rubbermaid bin that I used as the water reservoir for my saw. I've just syphoned out the water in hopes the water can evaporate & leave mainly dry cuttings to mix this weekend. (we shall see if May heat in Canada is warm enough for that purpose)

[Gulf]

Dig it out of the container and spread it out in thinner layers. It will dry much faster. I sieve mine with a normal window screen. And, yes there will be some cuttings that get through the screen which are much larger than dust size. I replace some sand with cuttings in the ratio for that. I don't know if it matters that much.