Mold Soap Sealer for Plaster. Instructions: Mix 1 part soap with 23 parts warm water. Brush onto clean plaster surface to seal. Wipe away excess with paper . How to Use SealDit™ Make Your Own Molds. Damaged Mold Not Using SealDit Food Grade Sealer Porous objects made from wood, plaster, cloth, paper and even some seashells must be sealed before .