seal off unused thru hulls: Epoxy or Polyester?

woodster · Dec 12, 2014

i like epoxy my self i use west system ...i have been told or heard that polyester does not bond as well when doing work like this but in the back of my mind i cant help but wonder what they did before west system

centerline · Dec 12, 2014

I would stick with polyester.. it is what the hull is made of and if you were to take it to a professional that is what they would use...

if you were gluing a plug or fitting into the hole, I would agree that epoxy is the proper adhesive, but for actually grinding, filling and fairing with cloth/roving, polyester is much faster product to work with and will hold every thing that it will ever be subjected to.

I will agree epoxy is stronger than polyester when everything else is equal, but polyester will stick as good as polyester sticks, and i can only assume that the rest of the boat isnt coming apart yet, so it must be good enough

... they have been using it for many years now with good results.

jibes138 · Dec 12, 2014

I'd go with epoxy for superior bond strength in a secondary bonding application. WEST is really good but I have also used MAS epoxy and have been happy with it. If you have the room apply glass to both sides of the hole and overlap the hole by a wide morgin on the interior side, this will give you peace of mind as the greater the surface area the greater the strength. You are not dealing with a very high pressure and the surface area of the hole is pretty small. If the hole is say three feet under water it will only be about 1.5 PSI water pressure. If the hole is say 1" diameter you are looking at less than a square inch so less than 1.5 pounds of force on the patch at 3 feet under water.

Alan Gomes · Dec 12, 2014

Go with epoxy as your first choice and vinylester resin as your second. The fact that your boat was originally made with polyester is irrelevant. The problem with polyester is that it is not so hot for secondary bonds, which is what you are doing here.

The only reason boat yards use polyester is because it is cheap--though perhaps they also like it because they are more familiar with it. It's also easier to wet out the cloth with polyester than with epoxy. But if price is a consideration then vinylester resin is also fairly inexpensive (compared to epoxy), wets out just like polyester resin, is quite a bit stronger, makes a better secondary bond, and is much more blister resistant. It's not as cheap as polyester but quite a bit cheaper than epoxy.

But for a small job like this I see no reason not to go with epoxy.

newage1461 · Dec 12, 2014

I was hoping to do the same thing in the spring, but was planning on using just epoxy. Is adding fiberglass necessary for this repair?

mitiempo · Dec 12, 2014

Yes, adding fiberglass cloth or roving is essential. Resin by itself has little strength.

The better yards would not use polyester. Epoxy or vinylester are good choices with epoxy the first choice. Polyester has good adhesion to green polyester but your hull hasn't been green since it was in the mold.

Most mat is not compatible with epoxy. The binders that hold the glass together dissolve in styrene and there is no styrene in epoxy. Best choice is biaxial 1708 or similar - a stitched roving with epoxy compatible mat attached to one side. It is strong and will build thickness fast. Grind a 12 to 1 bevel on the outside, the inside bevel need not be as large.

Capt jgw · Dec 13, 2014

Go with the epoxy. When a hull is built with polyester the resin does not cure until all layup is completed. Thats called a primary bond, and poly works fine in that mode. When you add new resin to old, fully cured layup, thats a secondary bond and poly sucks at that. Epoxy bonds well to almost anything and is the first choice, with vinylester second. As was mentioned, many yards use poly due to cost, but also because it's much easier to use. It only has to stick for whatever their warrantee period is, they don't care what happens after that.

Anonymous 121765 · Dec 13, 2014

Sher,

On a different point of view, have you given thought to just capping off the thruhulls?
This way, you always have the option of using them in the future. A threaded cap is a low cost ,low labor exercise. I have one that I capped off. I couldn't justify the cost & time.

It's not like anyone can see them.

CR

Capt jgw · Dec 13, 2014

If you just cap them, you still have to worry about the bedding leaking, freezing, and corrosion or getting blown off by a lightning strike if they're metal. If you're sure you're not going to need them again, remove them and repair the holes.

Merlin Clark · Dec 13, 2014

Epoxy and good barrier coat to seal it up before bottom paint. Following the minimum recoat instructions will give a good bond between paints.
The West System site has guides on fixing just about everything fiberglass.
The professionals in our area say "build with poly and fix with epoxy". Everyone I know (including me) gave up our poly after the first use of epoxy.

Bob J. · Dec 13, 2014

Not sure if it's true but I've always heard it's best to use epoxy for filling in anything below the water line.

gettinthere · Dec 13, 2014

West epoxy is expensive and amine.

Take a look at epoxyproducts.com for excellent quality epoxies as much lower cost and all amine free. I've used several of their products with good results.

just lucky · Dec 13, 2014

I tend to agree with captnron. you could use nylon fittings to alleviate the lightning strike theory. be a safer bet considering this sounds like your first fiberglass repair and as said before way less time and money.

mitiempo · Dec 13, 2014

Do not use nylon underwater. Marelon is fine as is bronze.

It will be a lot less expensive to glass them over than to replace them with Marelon.

Charlie Jones s/v Tehani · Dec 13, 2014

West is high dollar, but good. I began using it in 1976.

I now have over the years used MAS, Raka, System 3, and stuff form B and B Yacht designs, which is a generic.

Remember- there are really only a few companies in the US that MAKE epoxy resin.

The Gougeons have a fantastic tech support systems that has helped me several times over the years. BUT the epoxy is just plain costly compared to others. A gallon of west resin(no hardener), retail, runs $99. Delivered it's more.

I can get a gallon of resin from B and B, and a half gallon of hardener (2-1 mix) delivered for $86. And it works just as well. I've used it to build 7 boats so far

One thing I HAVE found is the 5-1 ratio epoxy from the Gougeon's will cure more quickly in lower temps than the 2-1 ratio stuff.

And for repairs on boat hulls, Epoxy is the ONLY thing I'll use. Recently did a close off on an old through hull- 7/8 thick hull- EIGHTEEN layers of glass outside, and 6 inside

Capt jgw · Dec 14, 2014

I've been using epoxy from US Composites and love it. Every bit as good as WEST and low and no amine blush versions. Current price is $75.50 for 1.5 gallons plus shipping from Florida. (about $23 to Michigan). They also have polyester resin and fiberglass.
uscomposites.com

just lucky · Dec 14, 2014

mitiempo, what is the issue with using nylon underwater? my boat has what appears to be a nylon through hull plug, sure don't want any issues on the water if they can be avoided.

mitiempo · Dec 14, 2014

Nylon absorbs water and is for above the waterline only. If a surveyor spotted it he would ask it be removed. Marelon is the composite to use underwater.

seal off unused thru hulls: Epoxy or Polyester?

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