Temporary repair to through-hull backing plate

[TCL]

I need to replace this (unused, capped) BTW through-hull; the backing plate is deteriorating and obviously has evidence of moisture.

As a **temporary** repair until I can get to the boat yard and haul out (preferred yard is about 90-95 nm away), I'm thinking of covering the backing plate with thickened epoxy resin. Someone suggested 5200, but I'm inclined to go with epoxy.

Have regular West System and a variety of hardener. Wondering whether I should get G-Flex.

I know that ideally all surfaces should be really clean, but I'm worried about causing some critical damage in trying to clean. I'll likely at least put a heat gun on low to remove any moisture.

Any opinions or suggestions would be greatly appreciated.

[AKA-None]

If the wood is very dry you could use some very thin epoxy that would soak in

[RaymondR]

Originally Posted by AKA-None

If the wood is very dry you could use some very thin epoxy that would soak in

There was a product called Everdure which was particularly good for that purpose, don't know if it's still available though.

[Uncle Bob]

Originally Posted by RaymondR

There was a product called Everdure which was particularly good for that purpose, don't know if it's still available though.

Yep, still around as are others much the same, however the wood needs to be dry, not just look dry, be dry.

[ggray]

I've used Git Rot epoxy with good results.

According to West System (Gougeon's) it's not a good idea to thin epoxy with alcohol or acetone so not sure how Git Rot is thinned.

But I did try to use it for a different task where it's lack of viscosity was helpful. Long story short, it never cured "hard", but it was tough with some give.

Perhaps that works well with (dry) rotted wood

[Manateeman]

Why? If the yard is 100 miles away. It looks like a bronze thru hull and a plywood backer. I’ve never seen a method to re glue wet plywood.
Do you scuba or can it be easily accessed from the outside?
Is water coming in? I’d be reluctant to do anything to disrupt it.
The nut is usually larger in diameter than the hole so it’s not going to fall out.
Well...in 99% of the cases ...so you could deal with the complete disintegration of the wood but the wood doesn’t look that bad.
Are you looking for a solution without hauling?
Mark

[Pandor]

You say you need to replace the throughull but then go on about how the backing plate is failing. It isn’t clear if your throughull is leaking or not. If it is leaking, it isn’t going to be caused by a rotting backing plate. Quite the contrary. So I don’t see the advantage of slopping epoxy over a rotten piece of wood.

[deblen]

If it is just the plywood backer that you are concerned about:
Can you wiggle the bronze thru hull from inside?
If not,I suggest leaving it alone til you haul out.I don't believe the plywood will disintegrate in the next year or so.
Pour some linseed oil in a rag & place around the thru hull,so that plywood gets well soaked. Much easier to do & to remove.
Cheers/Len


https://marinehowto.com/category/plumbing/

[TCL]

Originally Posted by Pandor

It isn’t clear if your throughull is leaking or not. If it is leaking, it isn’t going to be caused by a rotting backing plate. Quite the contrary.

It seemed to me that a rotting backing plate is evidence, not the cause, of a leaking through-hull. No?

[s/v Jedi]

I would use a heat gun to further dry and bring temperature up, then soak in epoxy resin. If at hand, I would use penetrating epoxy, but you can warm regular resin like West System 205 before mixing it with hardener to make it thinner.

Replace such backing plates with G10 next haul out and remove unused thru hull fittings and close those holes with fiberglass.

[TCL]

Originally Posted by Manateeman

you could deal with the complete disintegration of the wood

Please explain. Do you mean by simply tightening the nut down to the hull?

Originally Posted by Manateeman

Why? If the yard is 100 miles away.
* * *
Are you looking for a solution without hauling?

Just trying to do guard against the thru-hull becoming loose, and developing a serious leak, in transit.

[TCL]

Originally Posted by deblen

Can you wiggle the bronze thru hull from inside?

Yes, exactly. This is my concern. It's not sloppy loose, but there is a small, barely perceptible wiggle. Sorry for omitting this detail in my original post.

[carlosproa]

Originally Posted by TCL

It seemed to me that a rotting backing plate is evidence, not the cause, of a leaking through-hull. No?

It could be as simple as condensation on a cheap plywood backing plate. Or that area had standing water from rain. Lots of things can make that plywood rot.

You have not answered the question on wether there is an active leak from the gap between the plywood and hull. If none then leave it alone until you haul out.

[Bellinghamster]

Thru-hulls are sealed on the outside flange to the hull with sealant. if the backing rots and the fitting gets moved (turned or levered) it can break the sealant and leak a bit.
It won't (can't) leak significantly even if the sealant between the outside flange and hull is completely broken it still provides a "gasket" effect and water pressure is pushing the fitting into the hull. The remaining sealant around the threads and a (hopefully) reasonably sized hole in the hull will limit water flow to a trickle at worst - easily managed with a sponge and bucket or bilge pump.

In the very unlikely case that it does start leaking more than currently, you should be able to just tighten up the nut (while holding the fitting so it doesn't rotate in the hull) which will pull the flange against the outside of the hull tighter.

I wouldn't set off of a long cruise like that, but it'll certainly make the trip to the yard or last the rest of the season.

[Manateeman]

Exactly.