I know people have their opinions on poly over epoxy, but what about the opposite, hypothetically…same issues right? If you had to choose, which one would you opt for and why (assuming not going for a gloss finish)? I know you’re going to get more flex with an epoxy lam, right?
Thanks,
Not necessarily.
There are all kinds of different epoxies. Some are completely incompatible with polyester resins. For the most part epoxies stick to many more things than polyesters. How flexible the resin is depends on the modulus. “Aluzine” epoxy is formulated specifically to accept polyester resin top coats after the epoxy is well sanded.Many epoxies will accept polyester when a mechanical bond is created; this is achieved by sanding with coarse sandpaper providing some ‘tooth’ for the polyester to lock on to. The mechanical bond is NOT a chemical bond where the molecules interact with each other.Thicker poly gloss coats are prone to chipping, esp. after the board has expanded and contracted due to environmental conditions and use.
High grade epoxies developed specifically for surfboard or marine application are solids or have higher solid content than most polyester resin. Historically the epoxy resin cures much harder and requires starting sanding with a coarser grit (36 to 50 grit) than softer polyester resins. Additives for epoxy have been developed that make sanding easier and some claim to increase Barcol hardness while doing so, which seems contrary to easier sanding.
Epoxies cost more and if cosmetic considerations are important, be sure to choose a water white or non amber epoxy if you want true color work. Also one that contains UV inhibitors. The epoxy is more solid yet lighter than polyester resin…go figure.
To answer your question, go with epoxy for the lightest strongest end result. Go with UV polyester for quick and easy applications. I use aluzine epoxy laminate and hotcoats then sand out to accept a UV poly finish sand coat or gloss. Some guys have elected to float polyester hotcoats on epoxy lamiantes, to do this the epoxy cannot be fully rock hard cured. If it is you need to scuff sand the fiberglass layer (why would you do that?). If the laminates have been curing for some time and are not wet gooey but still not fully cured, more like hard cheddar cheese, that is the time to try applying the poly hotcoat…you may want to do a light wash with denatured alcohol if you feel you waited a bit too long, then apply the poly…still, an epoxy hotcoat will be superior to the polyester option. Some guys use different modulus epoxy for their lams and hotcoats to vary strength and scratch resistance somewhat like you are suggesting with the poly/epoxy combo.
So a resin research hotcoat over a poly lam is doable. Anything i need to do to the lam to prep it? Rough scuff?
Thanks in advance.
Sorry, I didin't keep up with this thread. I doubt lam needs any special prepping. Ask Greg Loehr @ RR. Personally I would favor the reverse application (poly over epoxy lams).