A publication on moulds from fibre boards is available from Stained Glass Supplies. This gives much more detail than this note can. However, the basics are outlined here.
Commonly available refractory boards are:
· Calcium silicate
· Standard fibre boards
· Armstrong ceiling tiles
They can be used bare (except Armstrong ceiling tiles) or hardened.
A question that will arise is whether to harden or not. This depends on the durability you require. A board that is not hardened does not require kiln wash when fired. However, as it is soft it is easy to break. A hardened fibre board mould always requires kiln wash or another separator. It does become durable and almost rings when tapped once it is hardened and cured. If the shape needs to be preserved for further use, hardening is advisable.
Usually hand tools are all that are required to get the results required.
Do any work on refractory boards outdoors if possible, and with a respirator. If you must do it indoors, have good ventilation, wear a respirator, and clean up with damp sponges or other absorbent material to avoid putting the dust back into the air.
Do you need to pre-fire fibre moulds?
Moulds that are small or thin do not erequire firing before using. Thick and large fibre moulds do need to have the binders burned out before use to avoid carbon marks on the glass.