Using PVA glue to waterproof a dry papier mâché 'balloon head/mask' before adding further pulp and laminations
The strength and rigidity of a papier mâché 'balloon head/mask' will be affected by the number of laminated layers of newspaper the children use. Older juniors working in pairs can build up as many as 12-15 layers during the course of an afternoon, which when dry form a very strong shell. Younger children may get bored with applying this number of layers so you may have to settle with less. Hence, the papier mâché shell will have less strength. If two masks are required (one for each child), the balloon head can be cut in half by the teacher, once it has dried, by using a Stanley knife. Further papier mâché pulp and layers can then be added. However, with a thin shell made from only a few layers there is an additional issue, namely that applying further wet pulp and layers will soften the shell because cellulose paste is water soluble even when dry. If it gets too wet, it can lose its strength and begin to collapse. One way round this is to coat the dry shell with watered-down PVA glue. When PVA dries it becomes waterproof and hence will provide a barrier between any new wet papier mâché and the dry shell beneath.