Mark Cortright on thu 28 feb 08
There seems to be some confusion on shelves-china ones cracking Geil not replacing warped
ones etc. Due to different uses and firing schedules your results may vary-some from mine.
I stack a cone 11 high fire car kiln with aprox 35 shelves per load at least 60 times a year-thats 30
glaze fires and 30 bisque fires so these results come from this work schedule most shelves are 12
x24. In the old days the good ones where silicon carbide which over time all warped and some
cracked-the thicker the better with 3/4 the standard thickness-the next level of better shelves for
me was the English dry pressed high alumina ones -1 inch thick-these worked better longer than
the carbide ones slowly and I mean very slowly warping-they never cracked on me except a few
corners.As they weighed 33 # apiece I swictched to bisgueing on 1/2 inch mullites for lite wieght-
so I had a seperate stack for glaze shelves and bisque-this was good for years then about 8 years
or so I swiched to 45 advancers for both kilns. These do not warp or crack and are very thin and
weigh 9# each for 12x24. I bought a china one a few years back and tested it (solid no expansion
cuts) and it warped. I then tried three with the cut outs from china and they are slowly warping. I
did this to test as I'm a curious person-I had Mel post all these results here over the years as well
as posting some myself when I'm on the site during my winter slower time should say i fire glaze
fires about 12 hours up and two day cools mostly.
Other's Like Vince used to torture the shelves in rapid cool downs in the old days and they crack
and warp sooner- some like to get the advancers wet and then blow them up and post that they
are bombs-I have found that if you take care of your shelves they will take care of you-your
results may vary but the above is what working with all these types has taught me over a long
period of time
My car kiln load can be seen here with advancers- Advancers are the best-english come in second.