Supplied in a plastic gripseal bag.
This shelf primer is used for coating kiln shelves and moulds before firing to prevent the glass sticking to the surface. Hot glass will stick to most ceramic or metal surfaces and crack as it cools, unless prevented by a separator such as shelf primer.
Each batch is kiln tested to ensure consistency from run to run.
Mix 1 part shelf primer powder to 5 parts (by volume) water. Stir the mix frequently during application. Each bag will coat approximately thirty 20" x 20" shelves when mixed 1 part primer with 5 parts water, with the required 5 coats per shelf.
Use five coats of primer on a new shelf or mould and also on subsequent applications. Apply the shelf primer with a wide, natural bristle brush, a Haik brush is ideal for this. Brush in one direction, then at a 90 degree angle, and then diagonally, applying as uniformly as possible. After applying five coats, dry the shelf or mould in your kiln at 260 degree C for 20 minutes. Take at least 30 minutes to bring ceramic moulds up to temperature, Mullite shelves can be fired up to temperature as fast as your kiln permits. Allow shelves and moulds to cool before use.
For steel, steep sided or non-porous moulds, the liquid shelf primer can be sprayed onto the mould. Heat the mould to 204 degree C in the kiln, then remove and spray the warm mould surface with primer until it no longer dries quickly. Reheat the mould and re-spray. Repeat this process until the mould surface is thoroughly covered with primer. Metal moulds with steep sides may require up to 10 applications.
Depending on the temperature at which you fire a shelf or mould, you may or may not need to clean and re-prepare it before your next firing. If you are not firing over 704 degrees C then you can reuse shelves and slumping moulds many times without reapplying primer, providing the primer has not been scratched through.
If firing above 704 degrees C then the shelves and moulds will need to be cleaned and recoated before each use. Scrape off the old primer with a wide tile scraper - scraping rather than sanding reduces dust. To remove primer from a shaped surface use a scouring pad.
If you don't kiln dry your shelves you cannot be completely confident that they are thoroughly dry. Surfaces that feel dry to the touch may still hold moisture that can cause bubbles, glass sticking and breakages.
Shelf primer is drying to the skin so wear thin rubber gloves to prevent chapping.
Avoid breathing shelf primer dust. Wear a respirator approved by NIOSH for dusts, and/or clean your shelves outdoors or with a good local ventilation system.
Keep the primer powder in a tightly closed container and store in a cool, dry place. Mixed, unused shelf primer will last for many weeks if kept covered.