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Old 29-07-2013, 10:37   #1
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Epoxy or replace throughull?

I'm replacing my head with a compostable one. I currently have a salt-water intake throughull for the current head and will need to either epoxy it off or replace the throughull and cap it. What are the recommendations out there? I've never done this before.... It is an old gate-valve by the way.
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Old 29-07-2013, 10:40   #2
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Personally? I'd remove the thru-hull, grind the area and then glass it and put some fresh gelcoat on.
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Old 29-07-2013, 11:11   #3
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Re: Epoxy or replace throughull?

Replace the gate valve with a proper seacock, much easier than glassing the hole. Unless you have about a foot all around the opening so that you can grind it prior to glassing. Take a look at the West System instructions:

WEST SYSTEM | Projects | Fiberglass Boat Repair & Restoration - Repairing machined holes in fiberglass

Not hard, but are you confident you can tackle this?
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Old 29-07-2013, 11:18   #4
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Re: Epoxy or replace throughull?

Either way is OK...if you might need the through hull later...say for a salt water washdown or air conditioner, etc...then an unused through hull is perfectly acceptable. Many people still attach a plugged piece of hose to it that reaches to the waterline...just in case...but others consider that overkill.

For a small (less than say 1 1/2 inch )through hull holes...most people can do a good repair with epoxy and some glass (try to avoid any matt with epoxy unless it states it's compatible). The are plenty of articles online on how to do it...the correct taper and preparation are important so get a few opinions from these articles.

Below the waterline gel is pretty much useless and the epoxy is a better water permeation barrier. That is unless you really get the wrong epoxy and the gel was some super vinyl ester product. But for the most part...gel isn't needed especially if things are gonna be bottom painted anyhow.
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Old 29-07-2013, 11:55   #5
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Re: Epoxy or replace throughull?

He's right. Grind a taper on the inside half the thickness of your hull and glass it over putting the large circle of glass down first alternating between mat and 10 oz or 18 oz cloth, putting on smaller circles so the edge doesn't get to thick. Then grind the same taper on the outside so there is no edge where you meet the old hole and inside glass patch. Then build out again starting with a large piece of mat and working to smaller pieces, alternating mat and cloth.
I'm using epoxy paint on my boat, but finish with what ever your boat has.
With care you can do a fine job that no one will ever know.
This was a 3/4" thru-hull
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Old 29-07-2013, 12:52   #6
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Re: Epoxy or replace throughull?

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Originally Posted by Chasing Summer View Post
......Then build out again starting with a large piece of mat and working to smaller pieces, alternating mat and cloth....
It's debatable whether you should start with a large piece and finish with a small one or the other way around. Starting with a large piece, all subsequent layers depend solely on the bond of that piece. If you start with a small piece, all subsequent layers touch the original laminate and creates a stronger bond - that is my opinion and the way I will do it on my boat.
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Old 29-07-2013, 13:16   #7
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Re: Epoxy or replace throughull?

If it's ground correctly, say with 24 grit on a 4-1/2 angle grinder, you'll get a good bite. Starting with a large piece you get 100% bond on the first layer. With a small piece you only get the edges each time you add a piece. Face it ... a bad lay up is a bad lay up whether you start with a large or small piece first.
I was taught this method by a profession glass mechanic. I used to do it the other way.
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Old 29-07-2013, 13:25   #8
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Re: Epoxy or replace throughull?

Just capping it you still have a vulnerable hole below the waterline. should you want to put one back in you can always cut another hole. You're best having as few as holes in the boat as possible.
On my boat I have 2 holes below the waterline:
1. seawater in: engine, galley sink, flushing water
2. overboard discharge: 2 holding tanks, bilge

You'll get as many opinions as there boat owners. Of course, this is just my opinion.
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Old 29-07-2013, 13:31   #9
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Re: Epoxy or replace throughull?

It all depends on how lazy you are feeling. The surest way is to do a glass job as others have described (personally i fall into the 'start small and work up' camp). No need to gelcoat afterwards. Once it's fair, paint it with 2000e or some other epoxy-based barrier coat. It's more impermeable to water than gelcoat and a lot easier to work with.
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Old 29-07-2013, 16:21   #10
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Re: Epoxy or replace throughull?

There really is no dfference in bond strength as the epoxy is the bond...the glass just gives it stiffness so big or small no matter.

Also...if you replace a thru hull with a quality one and place a capped hose on it and keep it closed...I'd say your chances of sinking from that are pretty slim....probably slimmer than many peoples "glass work" skills would put them in.

Either way done CORRECTLY is a acceptable result...poorly done and either can sink your boat in a stretch.
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Old 29-07-2013, 16:43   #11
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Re: Epoxy or replace throughull?

I am facing the same scenario (composting head, unnecessary thru-hull). I'd rather glass it in, but have two additional challenges:

#1. I can't grind and taper a large enough area on the inside; too close to a bulkhead. Can grind out perhaps 1/4 to 1/2 of the recommended area.

#2. My hull is cored (airex).

The first issue is probably the biggest. I'm not too concerned about fibreglassing the cored hull, but if I can't do it right, I'm thinking the cap might be safer.
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Old 29-07-2013, 16:49   #12
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Re: Epoxy or replace throughull?

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Originally Posted by Mike OReilly View Post
I am facing the same scenario (composting head, unnecessary thru-hull). I'd rather glass it in, but have two additional challenges:

#1. I can't grind and taper a large enough area on the inside; too close to a bulkhead. Can grind out perhaps 1/4 to 1/2 of the recommended area.

#2. My hull is cored (airex).

The first issue is probably the biggest. I'm not too concerned about fibreglassing the cored hull, but if I can't do it right, I'm thinking the cap might be safer.
agreed...why fight it?...who has heard of a well found, properly installed sea cock failing or falling apart within a decade or two or three.

if properly installed and maintained through hulls were that big of a risk who would install them? Certainly not manufacturers...they would go to all glass sea chests...

One issue though with seacocks with stainless in them...you have to open them weekly of so to keep the stainless from being in O2 depleted water and rusting.
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Old 30-07-2013, 11:24   #13
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Re: Epoxy or replace throughull?

One recommendation - if you decide to keep and cap a seacock, make sure you work it once in while - open and close - to prevent it from getting stuck.
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