Epoxy for repairs vs poly or vinyl

[chowdan]

So I've been going through this refit/rebuild of my sailboat. I've done bulkheads, stringers, misc things here and there - all with epoxy.

I used epoxy because everyone on the internet tends to recommend it over esters due to its adhesion ability along with its waterproofing ability.

I started using poly to add a "false" floor into my anchor locker to add drains overboard. I glassed over the plywood floor/tabbed in place with a few layers of 1708.

I've got to thinking about this and was hoping some wiser, more experienced people can shed some light on my ideas.

The first thing is that epoxy bonds incredibly well to just about any well-prepped surface. It will not only bond but be water proof and blistering will not occur. This is great for something that is constantly submerged(hull), but what about something that sees water intermittently? Do we really need that water barrier to be so "perfect"? I don't think so.

The claim of epoxy being better as an adhesive than any esters is great, but when looking at big repair jobs in yards, most yards will use an ester because it is the cost-effective solution and allows them to build up layers far faster than what epoxy would allow.

I've been thinking about this for a while now as I've spent quite a bit of money on epoxy over the last 2 years. MOST boats are built with poly/vinyl because it is cost-effective and works good enough in most cases.

The idea of using the "best" product seems to be meaning that one may be reaching for a product that is overly excessive.


Am I nuts to believe this?

[motion30]

I would have to say you are not wrong.. there are lots of old school boat yards still using polyester resin and doing it satisfactory work. VinylEsther resin has much improved secondary Bond strength over poly. Of course epoxy resin has yet again stronger secondary bonds. Personally I do not like the odor of the Esther resins, styrene I guess it is. The west systems are easy to use and provide tech support. There certainly is a cost premium only you can decide if that is worth it. Your complete boat is probably built with polyester resin

[chowdan]

Originally Posted by motion30

I would have to say you are not wrong.. there are lots of old school boat yards still using polyester resin and doing it satisfactory work. VinylEsther resin has much improved secondary Bond strength over poly. Of course epoxy resin has yet again stronger secondary bonds. Personally I do not like the odor of the Esther resins, styrene I guess it is. The west systems are easy to use and provide tech support. There certainly is a cost premium only you can decide if that is worth it. Your complete boat is probably built with polyester resin

Well that's good to hear that my thoughts aren't crazy!

I personally like West System's and the odor definitely is manageable, especially as a liveaboard. But considering the price of West to Fiberlay Polyester sourced from their shop here in Seattle is right around $35/gallon(with MEKP). Even with my commercial account purchasing from Fisheries, I'm looking at roughly $110/gallon for West(with hardener).

My thought recently has been if I need real water protection - for example, my anchor locker I figured the wooden bulkhead could use some water protection as well as tabbing on the top of the bulkhead. I used poly for this(as well as for the locker floor) and then did a quick coating of over the entire thing. My thought is that using 6 pumps of epoxy to overcoat the poly served two purposes -
#1 - it covers the odor of the poly
#2 - it adds that "water barrier coating"

[rbk]

I’ll second what motion said but I wouldn’t worry about water unless it’s below the waterline continuously immersed. Even then you could do the initial build up with poly/vinyl and too coat with epoxy but unless you’re using gallons and gallons of resin the cost benefits of ploy/vinyl aren’t that great for small projects for the added strength. The main drawback of epoxy for small projects is the cure time but is also less susceptible to rain/spray and some resins can cure fully submerses where poly will never cure after a light rain on it.

[chowdan]

Interesting! I had no clue epoxy can handle light moisture! I've always been diligent enough to not have that experience so that is news to me!

Over the last 2 years I've burned through about 10 gallons or more of epoxy. Not against it at all, just starting to realize that epoxy may not be 'required' for all jobs!

Originally Posted by rbk

I’ll second what motion said but I wouldn’t worry about water unless it’s below the waterline continuously immersed. Even then you could do the initial build up with poly/vinyl and too coat with epoxy but unless you’re using gallons and gallons of resin the cost benefits of ploy/vinyl aren’t that great for small projects for the added strength. The main drawback of epoxy for small projects is the cure time but is also less susceptible to rain/spray and some resins can cure fully submerses where poly will never cure after a light rain on it.

[rbk]

Just have to pick the right material for the project. If you’re doing numerous layers poly/vinyl will allow you to layer quicker, just make sure there’s no wax in it or you’ll have to wash it between each layer just like most epoxies. Unwaxed you can layer as soon as you want (usually a light tack to it). You can always finish with an epoxy top coat But remember it’s uv susceptible.

[Squanderbucks]

Having worked with all the varieties of common resins used in boating for more than 50 years there is a place for them all. Try to think of it like this.
Building or repairing large portions of the boat such as decks and bulls including bonding in stringers or bulkheads you can use any of the resins with good results.

Underwater hull repairs that are rather small to moderate or for surface - use epoxy.

If repairing or building high stress or structural components such as shaft log repairs, adhereing removed and replaced decks use epoxy.

My first choice is vinyl ester when considering a job unless I Convince myself there is a real reason epoxy is needed.

Building fuel tanks and such use vinyl ester.

Another reason to use vinyl or polyester is the variable and generally quicker setting times. Better control of working time.

As far as bond strength in most properly prepared surfaces that are properly faired beveled AND sanded to a nice 80 grit surface the bonds are all very good.

No matter which resin is used - once it is fully cured the next layers ALL depend on mechanical (80 grit) for the bond. New epoxy on wet or partially cured will chemically bond but there is no bonding magic once they materials are fully aged.

Certainly epoxy is the most expensive. I think it is harder to work with on larger surfaces and find it harder to “wet out” some of the heavier fiberglass materials.

[billgewater]

When in doubt, consider using an epoxy. An observation is that because epoxies have such great qualities (except UV degradation) many companies offer epoxies with all sorts of additives. If you use these products just ensure you understand just what the additives do. e.g. some additives (fillers) make for easier sanding but reduce the waterproofing or structural integrity. Some additives are deliberately designed to allow water vapor ingress, but retain the outstanding adhesion qualities. This applies to some epoxies used on brickwork or concrete where water vapour movement is expected. However, the standard marine use laminating resins are just great for wet areas.
If you use wood or plywood in any place where water may occur (this includes rainwater), then epoxies are probably the best material to use. e.g. when screwing or bolting into or through wood, drill and oversize the holes, fill with epoxy, re-drill then use the screws or bolts. So when water ultimately gets into the screw thread or bolt hole, the timber is protected. Timber can last forever if protected this way.

[Singularity]

It's sort of an obvious statement but it bears remembering that West Systems isn't the only epoxy option (but is expensive). For a lot of internal/less critical work...where epoxy is favored (e.g. wood protection or coating a fresh ester layup)...even crappy "bar top" epoxy can suffice.

Otherwise calling around to local plastics manufacturing companies may find someone willing to sell of a few gallons of high-quality resin from barrels that the company uses on a daily basis fabricating parts.

And of course be careful with buying epoxy from sketchy sources at a deep discount as resin can have a shelf life as well as being sensitive to improper storage.

[marshmat]

I generally concur with what Squanderbucks said earlier - there are places where you really do want epoxy, and places where the cheaper resins work just fine. They are more finicky and less forgiving; this is a large part of why we usually say "use epoxy" for repairs. If you accidentally mix a 5:1 epoxy with expired, turning-brown hardener at 4.5:1 and then apply it outside of its preferred temperature range, it'll probably still work just fine. But if you mix MEKP into polyester for 2.5 minutes instead of 3 minutes and then apply it 5° too cold, you'll come back in a day to find eight square feet of alternating cured & uncured swirls. Been there, done that.

West System epoxy is expensive because it's well-known / famous, and because there's a lot of R&D and marketing linked to it. Other brands work just as well, as long as you pick the appropriate components. East System and MAS are about 20% cheaper than West, and I've found EXP System at 30% to 40% cheaper. Vinylester is about 2/3 the cost of EXP System, and polyester is about 1/2 the cost. In some non-critical applications, I've been known to mix hardeners and resins from different brands (of the same chemical basis and mixing ratio, mind you - eg. East 833B hardener with West 105 resin works fine, but ester-based resins with any of the epoxy hardeners just gives you a big puddle of hazmat cleanup). That's generally not recommended if you're picky about achieving optimal strength and performance, but the chemical differences between marine epoxy systems are really very minimal.

[keyway]

I like epoxy. I don’t often use polyester/vinyl mostly because it’s simply easier to keep one product on hand rather than many different resins. Some of the thickening products don’t seem the mix as well with poly resins. The commercial fishermen around here almost always use poly resins on their boats with good results. Probably won’t hurt nothing to give it a try.

[thinwater]

Any links to tested secondary bond strengths?


I've used polyester and vinyl ester for repairs. Early attempts weren't great (as much as 45 years ago!), but I can make good use of esters now for many repairs. The things I've noticed are...

• Esters require a LONG scarf to avoid pealing, since the bond strength is ~ 4x less.
• Panels will be more flexible and weaker, meaning more glass and resin, meaning, you didn't save any money.
• Less waterproof; thin laminates in very wet areas can pass water and slowly dampen core even with no leaks.

I don't intend to go back to it. Epoxy is not that much more. I do like the way polyester handles, but that's not enough.

[pcmm]

I spent a long time in the "epoxy only" camp. For below the waterline I only use epoxy and for any structural repairs. For smaller things I'll mix it up. E.g. covered up some holes in the inside of my cabin sides (fiberglass) by layoun out some 1708 on a flat surface wet out with poly.. Once i cured I just cut out my patch (with bevels) and epoxied it in place. Took a very minimum if fairing to make it completely disappear. I did the same with some larger patches tool

I've even learned that you can gelcoat over epoxy!