Now, there are any number of legitimate reasons why one might choose one particular brand of epoxy over another--performance, cost, availability--but whether or not it blushes should hardly factor in. Why? Because it's just so simple to remove it. Besides, there is actual science behind the various epoxy formulations that determines the overall characteristics of that epoxy. Different epoxy brands are formulated differently, though generally using the same raw ingredients. One can read up on the pros and cons of various formulas, resin to hardener mix ratios, and the like to their heart's content; there's plenty of information available. We are not going to cover it here.
One of the more common epoxy resins used by boatbuilders and do-it-yourselfers is, of course, West System. Only a fool would truly suggest that West System is anything but excellent, but nonetheless it tends to be the subject of a lot of uninformed opinion looking for ways to discredit it somehow, sort of like finding reasons to dislike someone as emminently likeable as, say, Tom Hanks.
I mention West System only because West happens to be an epoxy whose hardener contains high levels of amines, and therefore forms blush with regularity on the cured surface. This is very well known by just about everyone who's heard of West System. Never mind the science behind why blush forms in some epoxies and not in others; but to somehow consider the formation of blush a flaw in the system is just silly. Yet, this is perhaps one of the most commonly-heard complaints, or means of attempted discreditation, about West System.
To that end, I thought it might be instructional to highlight exactly how straightforward blush removal is. Few things in boatbuilding or boat repair are actually simpler and less of a drain on time than washing away amine blush. If every aspect of boat work was this straightforward and plain easy...well, it'd be a happy day indeed.
Here are the expensive and complicated tools required to remove blush. These tools consist of plain water (I use a spray bottle), a Scotch-Brite pad, and a rag.
This photo shows a piece of recently installed tabbing which is fully cured, but has not been washed. You can see the gloss on the surface, some of which is caused by excess resin, but also from the amine blush on the surface.
To remove the blush, it's as simple as spraying the surface with water and scrubbing lightly with the Scotch-Brite pad. Then dry it off. It might take 10 seconds for a patch of this size.
When the blush has been removed, the tabbing takes on a markedly different appearance that makes it easy to determine that you have removed the blush. Note that the surface is duller in appearance.
Here is a large section of epoxy thickened with microballoons and cabosil--a typical fairing mix. Before washing, the surface appears deep purple and just a bit glossy.
After another exhausting 10-second wash, the surface looks like this:
Even a large area would take only a few minutes to wash in this way. However, it's also a cinch to not only avoid the formation of blush entirely, but to also eliminate the need to sand or prepare the finished surface in any way, by using Peel-Ply or other release fabric over the surface during installation. When removed, Peel-Ply leaves behind a clean, blush-free surface that is ready for additional lamination, or can be left as is.
My only point here is to highlight the simplicity of blush removal, so as to show why the potential formation of blush should not really factor into one's choice of epoxy resin.
