"I have coated wood or an epoxy surface with solvent free epoxy and it has “fish eyed” (often described in other ways such as ‘small holes’, ‘pulling away’, etc)"
There are several possible reasons:
a) Fish eyes are commonly reported when applying the second coat of a solvent-free epoxy on to a sanded surface. Remaining by-product and insufficient sanding of the first coat are very common causes. Sanding wet achieves by-product removal and gives a good key. When sanding dry it is especially important to remove by-product as it will only clog the sand paper. Use 80-120 grit.
b) If the work has been cleaned down with solvent immediately before recoating epoxy or after sanding bare wood then some solvent may have remained on the surface. Acetone or cellulose thinners are not as good as cleaning materials because they may be contaminated and their use sometimes leads to problems.
c) Check whether cleaning rag was contaminated with other types of solvent. It is likely that if other solvents were used previously, the customer may have inadvertently used one such as this to clean the surface.
d) If the work was wiped down with White Spirit - this is really bad news as it means that epoxy then cannot be used unless all traces are removed, which is almost impossible.
e) Wrong resin-hardener mix ratio can also give the same symptoms in some cases.
f) Traces of contaminant in the atmosphere - e.g. mould release agent aerosols, wax polishes, etc.
g) Some types of pigment dispersed in epoxy resin, may make the problem worse especially when coating is applied in a thin film.
h) Direct heat from the sun may also make problem worse.
i) Syringes can cause this problem if not cleaned out first. This is quite a common cause. Mixing cups or pumps do not have any surface contaminants.
j) If “fish-eyeing” is persistent when coating bare wood see next question.
"I am coating bare wood, I followed all your instructions regarding preparation and I get “fish-eye” effects."
If everything listed above has been done correctly then it may be one of those rare cases where the resin in the wood is causing the problem, even after the surface has been solvent-wiped. With some woods, such as oak, it is always difficult to wet out the surface and fish-eyes form readily. Note that oak is recognized as being a ‘difficult’ timber to glue. Resorcinol won’t work at all so epoxy is always the best alternative.