Permabond (with an A) is an adhesives company. I dunno if they make bonding agent, highly doubt it.
Permobond (with an O) is an Alcolin
bonding liquid product. It is used when the plaster is basically so worn out by the water ingress that it is crumbly and powdery like sand. No paint will take on it, it will come off in chunks. The bonding liquid will bond the particles of plaster sand together, and it will seep deep into the mortar and plaster. You will need to use it only if your plaster or mortar between the cracks are powdery. Personally I would not use it as a waterproofing, or as an additive to plaster, there are better products.
If you want to strengthen and waterproof the new plaster, then use a latex-based additive like Alcolin Latex-Bond or Alcolin Latex-Key (or alternatives). These products are designed to replace the water in the plaster mix, and will ensure some waterproofing and flexibility of the plastered finish.