98Mix

A pure terra cotta (red burning) clay that we dig straight out of the ground and grind into a powder. It is highly plastic and very smooth (fine particled). It is suitable in earth-mortars, green construction, ovens and heaters, pastes that need to be sticky and slurries that need to suspend well.

98Mix lumps on stockpile

This clay has a relatively low melting point (compared to fireclays). This makes it suitable as a fire-bonding-agent or as an addition to bodies to reduce their vitrification temperature. However, the melting point is certainly high enough for use in thermal mass ovens and heaters, as long as they do not exceed about 1850F (to avoid shrinkage, see fired bars shown below).

Fired bars. Top to bottom: Cone 4 (2150F), 2 (2100F), 02 (2030F), 04 (1950F), 06 (1850F).

If you are using this is in a non-ceramic application (e.g. for ovens and heaters) you likely are interested in its stickiness, bonding characteristics and dry hardness. Clays vary widely in these properties, 98 Mix is among the most plastic clays available (thus also the most sticky, slowest drying, most dry shrinkage (about 8%). Blend it with sand (and possibly fibrous material, like straw) to reduce the shrinkage (and therefore cracking). Experiment to find the best sand:clay mix for your application.

As noted, if exposed to the rain, this clay will slake and wash away (although much slower than dirt or other clays). It is possible to incorporate a hardener to give it more resistance the water slaking. Building supply stores have products suitable for this.

 Drying Shrinkage: 8.0-9.0%

Sieve Analysis (Tyler mesh):

     +48: trace
   48-65: 0.1-0.5
  65-100: 0.5-1.5
 100-150: 2.0-4.0
 150-200: 6.0-8.0

Fired Shrinkage:

 Cone 06: 1.0-2.0%
 Cone 04: 3.0-4.0
 Cone 02: 6.0-7.0
  Cone 2: 7.0-8.0

Fired Absorption:

 Cone 06: 10-12%
 Cone 04: 5.0-8.0%
 Cone 02: 0.5-1.5
  Cone 2: 0.0-0.5