That improves the quality and consistency of prepasteds. Some substrates, on the other hand, don't make for good prepasted products. It hasn't worked. On the other end, paperhangers themselves have learned how to work with the product, though not always in ways with which the manufacturers agree. Brown is fully aware that most contractors don't like to use water trays.
Contractors also use activators.
When there are problems, it's either because the surface is improper or hasn't been prepared right. One is that a surface can be too porous. Such a surface will absorb too much moisture from the paste, so it becomes too dry. Or, a surface can be too slick, and the adhesive will be unable to form a bond. Glossy oil-based paints are a good example of the latter.