Vermiculite, Ceramaguard

What is vermiculite?

Vermiculite is an extremely light water resistant refractory material. The correct name is ‘exfoliated vermiculite’ but common usage is to omit the ‘exfoliated’.

It has a number of applications in kilnforming;

• Compressed into boards as an underlay or mould material, or
• As a lightweight chunky material to create pebbly effects in underlays, or
• As a filler in castable mixes for moulds.
  

Exfoliation is a process wherein certain minerals are subjected to high temperatures so that they expand enormously to become light fluffy honeycomb-like particles of various size. The expanded material is then sieved and graded by size for its various uses which, in addition to the above also include:

• To hold moisture in potting mixes and in hydroponics
• As an absorber of liquids (sometimes sold as a cat litter)
• As a bulking additive to refractory materials
  

The most reliable source of small quantities of vermiculite granules is from garden suppliers where it will be labelled as ‘vermiculite’. It may not be as well screened to size as previously available as, like everything else, it is now coming in from China. If unaware of what it looks like, don’t buy products labelled ‘kitty litter’ or ‘cat litter’ in supermarkets, as it may not be vermiculite at all. Australian made vermiculite is more likely to be available through refractory suppliers, but in bags large enough to last several lifetimes. The major Australian processor is “Exfoliators Australia Pty. Ltd.

Glass sticks to vermiculite most tenaciously, so wherever it is used in kilnforming it must be battwashed or coated so that it doesn’t directly contact the glass.As loose crumbed material it can be used as a texturing agent under glass: gives a  ‘pebbly’ effect. Its is much less dense than gravel; so absorbs less heat if used for this texturing purpose.

Rather than trying to battwash fine particles, put some in a plastic bag with a small amount of dry battwash mix, or with straight alumina hydrate or kaolin, and shake until vermiculite particles are thoroughly coated. When placing in position, be careful not to pat it too much, else the powder on the high points will be removed: all ones good work will be in vain.

Compressed vermiculite board

Worldwide there are a number of makers of products for heat or sound insulation.

Heat insulating board is made by Thermal Ceramics in Adelaide and is available through their state offices. Minimum thickness is 25mm. It is fine grained, soft and rather crumbly, but can be hardened somewhat by coating after shaping with colloidal silica or sodium silicate: and then battwashed.

Skamol of Denmark make boards in a wide range of grades and thicknesses, but they are not widely stocked here. They are mentioned here because they can be of use if they can be found.

Armstrong World Industries produce a range of acoustic and fire retardant ceiling tiles. It is made in America and sold under a number of brand names, the most common name in Australia is Ceramaguard. It is available here through suspended ceiling distributors.

Ceramaguard

is widely used as a mould material but less so as a shelf. The standard sheet is about 1200 x 600 x 16mm (4ft. x 2ft. x 5/8inch).

It has a vinyl coating on the face side and this burns off during the first firing.

Some of the particles are fairly large and the face side has crevices created by the gaps between these particles. It is easy to cut with wood saw drill or hacksaw blade but tends to crumble at the edges unless care is taken. Cut or damaged edges can be sanded and built up with a mixture of kaolin and colloidal silica;or battwash powder and colloidal silica. Allow all surfaces to dry before applying final coats of battwash without colloidal silica.

Ceramaguard  and all other vermiculite products must be battwashed.