Invention of PVA
Before PVA glues became commercially available in the 1960s, the most common type of glue was called "rabbit glue." It came in the form of granules and had to be heated up in a glue warmer before it could be used. PVA can be used directly from the bottle. The increased convenience of using PVA glue made rabbit glue obsolete, but PVA was later found to have other uses. It can be used to seal concrete, and makes a superior paper mache for school projects.
Advantages of PVA
PVA is water-based, which is why it can be applied directly from the bottle without being heated up first like older types of glue. If the cap is left off the bottle of glue, it won't dry up right away. PVA is usually applied by just squeezing it out of the bottle, especially with popular PVA brands. This makes PVA glues easy to use. PVA is also soluble in water, meaning that it can be cleaned up just by applying some water and a towel. When PVA dries, the glue is clear, so the glue line is not as obvious or unsightly.
Disadvantages of PVA
Some of the disadvantages of PVA glue are caused by the same characteristics as the advantages. Because PVA is water-based, anything glued together with PVA can start to come apart if it is exposed to water. For the same reason, objects being glued together with PVA need to be clamped down in a press until they dry, or the water in the glue will make them curl. In addition, the glue can drip or run until it dries in place, possibly leaving a mark on the finished project. It is important not to store PVA in freezing temperatures, because the cold will cause the polymers in the glue to decay and the glue will no longer work.
Tasks PVA Is Not Suited For
PVA glue can't be used for everything. It has a corroding effect on anything made of metal, so it should not be used to glue metal together unless a coat of varnish is applied to the metal first to protect it from the glue. PVA will not be effective on any surface that is non-porous. In addition, it is used most effectively near room temperature. Because freezing temperatures destroy PVA, this type of glue cannot be used for outdoor winter tasks. PVA glues are not designed for filling gaps, but can be used somewhat effectively for this purpose when mixed with sawdust.