Epoxy or Polyester, how do you know which?

[Simi 60]

It's not really a discretionary item. It will be our home, so, yeah definitely epoxy.

Fair enough but my point is that a few litres of epoxy is neither here nor there compared to boat ownership, marina fees (for most) and fuel usage on a weekend

I'm not just going to throw a blue tarp over the boat and call it good to go.

I never suggested anything like that

I'm really open to using quality stuff and not wedded to West. If there are any you care to recommend that are available in the U.S.A., please do.

Boat design forum might be the place to go.
I have no idea what other brands and breeds are in the US, I do know that the stuff I buy in oz was almost half the price of west and only a few dollars more than polyester.

Many of Australia's fastest composite multihulls have been built using that same brand of resin since the early 90's, so its more than up for the job.

 

[boatpoker]

It's not really a discretionary item. It will be our home, so, yeah definitely epoxy. I'm not just going to throw a blue tarp over the boat and call it good to go. I'm really open to using quality stuff and not wedded to West. If there are any you care to recommend that are available in the U.S.A., please do.

With one hi-tech exception involving nomex honeycomb core and carbon fiber,
I 've built boats and cars using no-name epoxies from a wholesaler and never noticed any problems.

 

[Lepke]

I've used West Systems for along time. I know there other good epoxies. I've had a lot less trouble mixing West than others. The usual problem was they got hard too fast. I had a couple batches get hot. One small batch was so hot I had to drop it, and later grind it off the deck. Could have been me. Old guy new tricks.

 

[rgano]

Just did it Saturday. Bonded in a piece of Coosa board that had 1/4" of fiberglass (polyester) already on it, with West System and bonding filler. After it cured and off gasses (about 5 days), I sanded it and wiped it down with acetone. 2 layers of gelcoat, and the project in the anchor locker is done. No issues with adhesion.

View attachment 108878

This picture is from 5 years ago when Sean increased the divider height. No adhesion problems.
View attachment 108879

Ted

Ted, just curious; what was your reason for gel versus paint down there in the chain locker, or for that matter why coat at all?

 

[Comodave]

I've used West Systems for along time. I know there other good epoxies. I've had a lot less trouble mixing West than others. The usual problem was they got hard too fast. I had a couple batches get hot. One small batch was so hot I had to drop it, and later grind it off the deck. Could have been me. Old guy new tricks.

I have had almost fire a couple of times when I left the mixed epoxy in a cup and had it too deep. Thermal runaway...

 

[Comodave]

I've used West Systems for along time. I know there other good epoxies. I've had a lot less trouble mixing West than others. The usual problem was they got hard too fast. I had a couple batches get hot. One small batch was so hot I had to drop it, and later grind it off the deck. Could have been me. Old guy new tricks.

I also like West epoxies. I know they cost a bit more but that is ok. I bought a gallon of Total Boat 5:1 epoxy and really didn’t like it, no specific reason. I still have almost the whole gallon left and I just ordered a new gallon of West since I was about out.

 

[Sea Level]

It's a little hard to tell from the photos but it looks like there's no cloth or mat involved, just a stress crack in the gelcoat sprayed over resin coated mahogany beams?
Lots of builders did it that way.

 

[sean9c]

Lots of good epoxies out there. West System is good and easily available. West Marine sells it. It's a 5:1 mix ratio so you pretty much need their pumps, which work fine but are just another thing. System 3 is another good one and I think WM sells it. It's a 2:1 mix ratio so easier to mix just using graduated cups. I think System 3 has a hardener that's good down to 32F. I've pretty much always used WS and using their fast hardener in winter here in the PNW have never had a problem.
Don't waste your time with a polyester just find an epoxy from a local supplier and go with that.
In case that you don't know. With epoxies you don't vary the resin/hardener ratio like you do with a polyester.

 

[DNT99611]

I like System 3 better than West System for two reasons. 2-1 mix is much more forgivable of small mixing errors and it is much less likely to blush.

 

[Tator]

We've used System 3 for rebuilding our boat and on all projects since then. Good support and products. We use their no-blush Silvertip product and their premixed fairing compounds. I also like not having to use a pump and being able to mix small amounts at a 2-1 ratio in small medicine dose cups.

Tator

 

[ghost]

It seems to be, and the surveyor said it was and that it was probably caused by an event with the Bullfrog dink w/20 HP Yamaha sitting up there. Just to keep an eye on it and repair if necessary. I would like to do it right away just to keep any moisture from getting in there. If you enlarge the indicated area you will see the cracks.

BTW, it's in Anacortes and I have to run up from Kirkland.

I make that trip at least once a week. Live in Kirkland, boat is at Anchor Cove.

Hard to go wrong with West. I prefer system three, especially silver tip if compatibility is at all a concern as it doesn’t really blush and varnish doesn’t crater on top of it. It would probably play nice with gel, though system three recommends a dedicated resin for that as a go between. West is really convenient with the calibrated dispensers and silver tip is expensive. Though the biggest expense is waste. Fisheries with an account is cheapest so you don’t pay West Marine prices when you run out.

When you get to the gel coat, definitely spray it. All you need is an inexpensive preval sprayer and an assortment of fine grit sandpaper, (60 through 800). You can get gel coat locally in Seattle from Gel Coat Products on aurora, or Spectrum. I’ve had excellent product from both.

 

[sean9c]

Thought of something that not much talked about, viscosity. It's really only important if you're laminating but high viscosity can make the already slow wet out of epoxies take even longer. The lowest viscosity that I've found, other than some specialty resins, is West System using their 207 hardener. 207 is a specialty hardener usually used for projects that are clear finished but works great for laminating. It's potlife falls between the WS fast and slow hardener. Next in line for viscosity is WS using their slow hardener, it gives you about the same viscosity as System 3 laminating resin. The other resins that I've looked at all have higher viscosities

 

[Comodave]

I have not really had a problem wetting out 1708 with epoxy. I think that poly resin may wet out quicker but I have not tried poly resin with 1708 only mat. Mat doesn’t work well with epoxy due to the binders used to hold the mat together. I used a lot of mat repairing damages where the PO managed to hit the dock, all over the hull. The repairs weren’t deep enough for 1708 to be needed so I used mat with poly resin there. If it is structural I only use 1708 and epoxy.

 

[rslifkin]

They do make epoxy compatible CSM, you just have to look for it. The regular stuff meant for poly won't work right with epoxy, but it should work with vinylester.

 

[Simi 60]

Thought of something that not much talked about, viscosity. It's really only important if you're laminating but high viscosity can make the already slow wet out of epoxies take even longer. The lowest viscosity that I've found, other than some specialty resins, is West System using their 207 hardener.

One of the reasons I stopped using west was it was thick compared to the resin I currently use.

We were doing vac bagging and resin infusion of foam, kevlar, carbon composites and needed better.

West was ok for hand laminating but its nothing special,

 

[Steve DAntonio]

I saw a suggestion on another thread that said, if you have screw holes or you a going to make any, in your deck, you should drill an oversized hole and fill it with the proper resin, epoxy or polyester. There was no information on how to know which to use. It just said that it had to match what was used on the deck GRP. My question is, how do you know what that is, or how can you find out? Does it really matter? I'm looking at cracks that need repair also. I've never worked with fiberglass before but, I'm up (down?) for learning. I'll try to include a picture.
View attachment 108877

The existing polyester resin is fully cured, so there is no compatibility issue. As others have noted, epoxy's superior adhesion qualities make it the go to product for this application. This article will walk you though the reefing and backfilling process, step by step https://stevedmarineconsulting.com/cored-composite-deck-hardware/

If you are new at this, West System's Fiberglass Repair Manual is a helpful companion https://www.westsystem.com/wp-content/uploads/Fiberglass-Manual-2015.pdf They have a number of videos as well.

 

[jbloyd]

Thanks for all the great information. I feel a bit more confident about doing this.
I had the P.O. on the boat yesterday and it had been raining a lot. Water dripped from the cracks and and many of the hanging drips were brownish in color which seems to me to indicate an involvement of the core getting wet. I asked him about how he bedded the screws holding the channel for the slider and he said he just put a sealant on them and screwed them in. I suppose scope creep on something like this is inevitable.

 

[Comodave]

Thanks for all the great information. I feel a bit more confident about doing this.
I had the P.O. on the boat yesterday and it had been raining a lot. Water dripped from the cracks and and many of the hanging drips were brownish in color which seems to me to indicate an involvement of the core getting wet. I asked him about how he bedded the screws holding the channel for the slider and he said he just put a sealant on them and screwed them in. I suppose scope creep on something like this is inevitable.

That is the way it always goes... You think it will be a quick fix and it inevitably turns into several days work. I would be definitely concerned about the brown dripping from the leaks. Is this from the deck or a window?

 

[Alisske]

Amine is water soluble, so fresh water will remove.
If the epoxy is clean, sanded and primed with two part primer, gelcoat adhesion is not an issue. One part primer sorta maybe works a bit sometimes.

Amine blush has caused me issues in the past. (Spots not curing in ideal conditions). On the redo I washed the surface with soap and water like i was cleaning a crime scene. No issues.

I think most failures of polyester over epoxy come from the amine and folks not washing polyester for prep. .

BTW, the spots were a few spots i hit right before i sanded (but had previously been washed). The act of spot sanding raised fresh amine.

 

[jbloyd]

That is the way it always goes... You think it will be a quick fix and it inevitably turns into several days work. I would be definitely concerned about the brown dripping from the leaks. Is this from the deck or a window?

The picture is at the beginning of the thread.

 

[Comodave]

If you are getting brownish drips from the crack in the first post photo, then I would suggest that you deal with the leak of water getting into the area first. I would track down the leak and reseal it however is necessary to stop the water getting into the area. Then let it dry inside, and you may have to grind it a bit to let the water out the bottom. After it is thoroughly dry then do the epoxy repair on the bottom. But you need to stop the water getting into the top before you seal the bottom or you will seal the water in and promote rot. There is a good article on sealing at marinehowto.com.

 

[Olebird]

I use this TotalBoat Flexible Epoxy Adhesive for filling small holes, repairing or prepping for screws and repairing spider cracks. Good adhesive and has enough flex to stop cracking.

 

[Rufus]

I used MAS epoxy with layered glass mat for fixing larger divots, and thickened MAS (micro bubbles and other suitable fillers) for fairing prior to actual barrier coat. MAS has very low VOC and zero amine blush. Multiple coats of Interlux 2000 for the full barrier coat. Interlux bottom paints over the barrier coat.

 

[ProMaritime]

If you always use epoxy putty for fill or epoxy resin with fiberglass cloth with larger repairs you have no problems. I haven't used polyester resin or putty for over 25 years.

 

[Comodave]

I use polyester resin if I am doing a non structural repair that only uses mat glass. Epoxy doesn’t wet out mat well due to the bonding agent used in the manufacture of mat. OTOH, the mat used in 1708 isn’t bonded with the agent but rather sewn together with the 2 layers of the glass so epoxy wets out the mat layer easily.

 

[psneeld]

I am no pro but have worked with and learned from a few.


There are plenty of applications that are suitable for poly and vinylester resins as well as epoxy.


For each project, research a bit and you can usually find alternative methods depending on the situation.

 

[Steve DAntonio]

I am no pro but have worked with and learned from a few.


There are plenty of applications that are suitable for poly and vinylester resins as well as epoxy.


For each project, research a bit and you can usually find alternative methods depending on the situation.

Agreed, epoxy has its place, however, vinyl ester has many attributes. I cringe when ever I see a bottom relaminated with epoxy, it's murder to wet out, whereas VE is far easier and very epoxy like in its characteristics.

Epoxy is easy to use for for non-pro's because of the mixing method and no VOCs or respirator required. It's ideal for core closeout/reefing and backfilling. However, for a hull or large cabin repair, or relam, I would use VE resin.