ADVANCER® Kiln Shelves FAQ
1. Do I need to use kiln wash on my ADVANCER® shelves?
While many individual customers report that they do not need to use a wash coat on their ADVANCER® shelves, we generally recommend using a suitable high alumina wash on ADVANCER® shelves – particularly in studio or classroom settings where multiple users are present.
Due to the extremely low porosity of ADVANCER (less than1%) vs. conventional silicon carbide
(18% typical) and cordierite (30% typical), it is true that there is much less of a tendency for glaze to penetrate into or stick onto the ADVANCER surface. Never the less it is still possible for glaze to react with the protective oxide glass surface of ADVANCER, especially at higher temperatures, and bond onto the ADVANCER surface. Glaze drips are usually easily removed without grinding because extremely low porosity of ADVANCER. On the other hand glazes that volatilize at temperature, leaving a fine mist of glaze on the shelf may require light grinding or sanding for complete removal.
2. What kiln wash is recommended for ADVANCER shelves®?
Kiln wash for ADVANCER® should be high in alumina. Many commercially available kiln washes are high in silica and are not recommended for ADVANCER due to the tendency of silica to interact with the oxide glass layer of the shelf. In some cases alumina hydrate can be substituted for silica (flint) in an existing wash formula with success.
Please contact us for a wash recommendation or with questions regarding your specific wash formula.
3. I have heard that porcelain clay bodies stick to ADVANCER® shelves?
Due to the high amount of flux used in porcelain clay bodies (up to 50% typical) to achieve translucency, it is not uncommon for porcelain clay bodies to stick to the ADVANCER surface. The higher the firing temperature is, the greater the opportunity for the flux to interact with the oxide glass layer of the shelf. Pieces with trimmed foot rings supporting larger pieces, like bowls, tend to stick more tenaciously than broad, flat bottomed pieces due to increased pressure on contact area.
Some cone 6 porcelains may not have a sticking problem on ADVANCER. Please contact us for more specific information. You may also refer to the article “Why Porcelain May Stick to ADVANCER” on this website for a more technical explanation.
4. Do I need special posts for use with ADVANCER® shelves?
In general you do not need any special posts for use with ADVANCER® shelves. Round or square cordierite posts with a hole down the center will work just fine. Hard fire brick soaps (2-1/4” x 2-1/2”x 9”L) in various lengths may also be used. It is not advisable to use full hard bricks (2-1/2” x 4-1/2”x 9”L) as posts with ADVANCER due to potential uneven thermal gradient problems created by such massive shelf/post contact areas.
Wadding between shelves and posts is frequently used to promote setting stability, and is an acceptable practice with ADVANCER shelves. It is also recommended to use a suitable kiln wash on the ends of posts to prevent sticking between ADVANCER shelves and posts after repeated firings with posts in the same spot on the shelf surface.
5. Because ADVANCER® shelves are thin, is it better to use a four point stacking system?
ADVANCER® shelves are up to 19 times stronger than one-inch thick cordierite shelves! Therefore it is unnecessary and not recommended to use any arrangement other than a 3 point stack. This is the most stable system and puts the least amount of stress on any single shelf.
6. Do I need to flip ADVANCER® shelves to even out potential warping problems?
No. ADVANCER® shelves will not warp under typical pottery firing conditions even after repeated firings to cone 12 under heavy loads.
7. I’ve heard that ADVANCER® shelves can explode if they get wet?
Due to the extremely low porosity (less than 1%) of ADVANCER® kiln shelves, it takes prolonged exposure to a direct and continuous moisture source such as rain, standing water from a floor or condensation to penetrate the shelf. Water is slow to get in, and once in it is slow to get out. Therefore a temperature controlled dry out schedule must be observed prior to taking the shelves to normal firing temperatures. Slow bisque firing is not adequate to insure complete moisture removal! If you know or suspect that your shelves have water in them, you must follow the dry-out schedule outlined in the Saint-Gobain Technical Bulletin Warning “Storing and Drying Requirements for ADVANCER® Refractory Components.”
If you are uncertain about moisture exposure problems with your shelves, please don’t hesitate to contact us!
8. Will kiln washing ADVANCER® shelves or getting a few drops of water on them cause a problem?
No. It takes prolonged exposure to a continuous moisture source to cause problems. It should also be noted that there is no evidence of atmospheric humidity causing moisture problems with ADVANCER® shelves. They are in use almost everywhere in the world!
9. What about firing damp pots or pots with wet glaze on them?
Generally this will not cause a problem, but we recommend letting green or freshly glazed pots dry completely prior to firing on ADVANCER®.
10. What about using ADVANCER® shelves in a soda kiln?
ADVANCER® is often used in soda kilns. Clean-up of soda drips from the surface of the shelf is a breeze since the low porosity of ADVANCER does not allow the soda glass to get much of a grip on the shelf. Spraying or dumping soda into the kiln firebox and having it naturally disperse throughout the kiln is the preferred method of introducing soda into the kiln. Soda can also be introduced in a dry form when combined with whiting, with good results. We do not recommend spraying liquid soda solutions directly onto ADVANCER® shelves through a port hole, since this practice may lower the temperature enough to the point of soda contact to cause a significant temperature gradient across the shelf leading to cracking, thermal shock and failure.
11. Can I use ADVANCER® shelves in a Raku kiln?
No. Direct flame impingement on ADVANCER® shelves early in a firing will usually cause thermal shock and lead to shelf failure. ADVANCER can withstand rapid heat-up and cool-down, but temperature across the shelf must be even, which is never the case in Raku kilns.
12. What would cause an ADVANCER® shelf to crack during a firing?
The vast majority of failures with ADVANCER® shelves can be traced to uneven temperatures across the shelf (thermal gradients) causing thermal shock and shelf failure. This can occur on heat-up or on cool-down for a variety of reasons. Typical problem areas in kilns include the bottom layer of shelves in a car kiln, where the seal between car and kiln is not tight permitting cold air to rush in when the kiln is shut off, using posts that are too massive (see “Do I need special posts for use with ADVANCER shelves?” above), direct flame impingement on shelves early in the firing, overly large sight ports permitting cold air to cool off shelf areas unevenly, shelves too close to damper areas causing uneven cool-down of shelves in close proximity to damper.
If you have any concerns regarding the use of ADVANCER shelves in your kiln, please call to discuss your particular situation to make sure that ADVANCER is right for you!
12. Do you recommend ADVANCER® shelves for use in wood-fired kilns?
ADVANCER® shelves have been used successfully in many wood-fired kilns. However, they should not be used in areas where there will be direct flame impingement early in the firing, such as fire mouths and areas adjacent to checker walls in second chambers. In these areas a conventional, thicker silicon carbide is preferred due to their ability to better withstand thermal shock. Wadding on brick posts under ADVANCER shelves is also recommended to minimize surface contact areas with massive kiln furniture.
13. Are ADVANCER® shelves safe to use in electric kilns?
Yes. Although some forms of silicon carbide are known to conduct electricity, ADVANCER® is a relatively poor conductor of electricity due to the oxide glass layer present on all ADVANCER shelves. Be sure to select the correct size shelf for your kiln and make sure your kiln is in good repair with no elements hanging out of the grooves where they can sprawl out onto shelves. Finally use common sense and never reach into an energized electric kiln!
14. How are ADVANCER® shelves made in comparison to conventional silicon carbide shelves?
Unlike conventional silicon carbide shelves that are made from a grainy, semi dry mix that is ram pressed into molds, ADVANCER® shelves are made from an extremely fine grained mix of silicon carbide that is slip cast into plaster molds and then high fired multiple times. The fine grained, tight structure of ADVANCER shelves is one of the key reasons why they stay flat and can be manufactured in thin cross sections with exceptional strength. All corners and edges are rounded to produce smooth surfaces for ease of handling and strength.