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Old 03-05-2017, 12:38   #31
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Join Date: Sep 2016
Location: Fiji
Boat: Oyster 56
Posts: 25
Re: Epoxy on gelcoat and installing thru-hull fittings with epoxy

I just replaced all of my thru-hulls with the trudesign. The only metal parts under the waterline are now shaft, prop and a well epoxy-protected keel.

My boat has 12 years, but was on hard for 2 or 3 years. The thru-hulls and valves looked as new from the outside but were pink and corroded inside. They were made of CR-brass, certainly this metal is not ok for marine use.

I removed all the AF with the scraper, sanded to the gelcoat, and applied 5 layers of barrier (international). The TH were mounted before i applied new AF.

And now to the trudesign. Before installation, i made a test with the cut-off remains of the thru-hulls. I used epoxy to bond them, with clean surface and rough surface. After two days, i could easy breake the two shiny parts, where to break the roughened and sanded surfaces i had to use the pliers. So my opinion is, the material does not produce a good bond as the producer says if not treated properly.

It is important to roughen the surface of the thru-hull and the nut with the sand-paper, i also made several scratches with olfa-blade.

For the installation, you first cut the thru-hulls (i kept the distance between the nut and valve less than 1cm to have more physical strength), then roughen the surfaces and protect the first 30mm of thread where ball-valve will be screwed-on with a masking tape (when you push the TH through the hull, there is fresh epoxy that would fill the threads).
Then you use thickened epoxy and apply it with a brush to the hull and a thru-hull. After that the thru-hull is inserted into the hole, and pressed firmly. From the inside, other person fills the voids - if any - and applies a layer of epoxy where the nut will sit. I did not use the washers supplied with the TH. Then the masking tape is removed and the nut is gently tightened - so you can see how some epoxy is coming out and builds a collar.

Few days later i installed the valves, i used LOCTITE 55 - Thread Sealing Cord. Important - do not follow the thread when you wind it, just do it randomly and crossed. I also made several final turns - more than recomended - at the inner end point.

I installed 13 truhulls and valves, and after 10 days in the water, everything is still dry
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epoxy, gelcoat, hull

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